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DOCUMENT'RESUME

ED 218 490 CE 033 120

TITLE, Military Curriculum Materials for'Vocational andTechnical Education. Drainage,

INSTITUTION Ohio State Univ., Columbus. National Center forResearch in Vocational Education.

SPQNS AGENCY Office of Education (DHEW), Washington, D.C.PUB DATE [81]NOTE 188p.; This,course was adapted from U.S. Army

-curriculum materials.

EDRS PRICE MF014/PC08 Plus Postage.DESCRIPTORS ,*Construction (Process); Construction Ma,teritils;

Independent Study; Postsecondary Education;*Programed Instructional Materials; Secondary'Education; *Technical.Education; Units of Study;*Vocational, Education; *Water

IDENTIFIERS *Drainage;t0Military Curriculum PrOject

ABSTRACTThis individualiged, self -pace cisilrse for

independent studliin water drainage was adapfed rom militarycurriculum materials for use in vocational educa ion. The course',Amides basicinformation for the design bf simple drainagestructures for roads and airfields. Some job skills included aredesigning and constructing ditches and culverts; designing subsurfacedrainage facilities; designing and using ponding areas; and designingcheck dams and drop inlets. The course consists of five lessons, eachcontaining a lesson objective, readings, andreview exercises. Thecburse can be-used as.a sub-unit in environmental control,construction, or some types of agriculture courses. Each lesson hasan objective, a coded text, exercises, and answers keyed to'the textfor student self-evaluation. A course examination of 50multiple-choice questions is provided, but no answers are available.Supplementary charts and graphs are provided. (KC)

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'****************************************************************1****** Reproductions supplied by EDRS are the best that canbe made ** .1. from the originaldocument.' . * g,*******.**************************************************************** r\

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MILITAY CURRICULUM MATERIALS

The military- developed curriculum materials in this course

, peckage were selected by the National Center for Research inVocational Education Military Curriculum Project for.dissem-ination to the six regional Curriculum Coordination Centers and,other instructional materials, agencies.' The purpose ofdisseminating these courses was to make curriculum materialsdeveloped by the military more accessible to vocationaleducators in the civilian setting.

The-course materials were acquired, evaluated by projectstaff and practitioners in the field, and prepared for

ditsatination. Materials which were specific to the nilitarywere deleted, copyrighted materials were either omitted or appro-

val for their use was obtained _These course packages containcurticalvm resource materials Which tan be adapted, to supportvocational instruction and curriculum development.

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The National CenterMission Statement

The National Center for Research inVocational Education's mission is to increasethe ability of diverse agencies, institutions,and organizations to solve educational prob-lems relating to individual career planning,

--preparation, and Orogressidn. The NationalCenter fulfills its mission by:

Generating knowledge through research

Developing educational programs andproducts

Evaluating individual program needsand outcomes

Installing educatiOnal programs andproducts

Operating information systems and `,services -

. . tConducting I dership development andtraining prOgr s

FPR FURTHER .INFORMATION ABOUT I' ' 'Military Currictilurq Materialk. .. ,,

WRITE OR CALL , .Program InfOrmation OfficeThe National Center for Research in Vocational

Education .-The Ohio State UniversitY1960 Kenny Road, Columbus, Ohio 43210

4. Telephone: 614/4863655br Toll Free 800/848.4815 within the continental ,U.S.(excipt Ohio)

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.11J1ilitary'Curilculum.-Materials for

Vocational andTechnical Education

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tnforjnation and Field.Sr.:rvices.Divir,ion

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The i!.70ion-11 Center for Rese.,arcliin Voc.-,,tional Education

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MilitaryCurriculum 'Mated 6lsDissemination Is . . .

...Qr.. 4444 444.4414:4.444.4444.44.4.4444d4j

, .an activity to increase the aetessibility ofmilitary developed curriculum materials tovocational atcl technical educators.

This project, funded by the U.S. Office ofEducation, inclAides the identification andacquisition of curriculum materials in printform from the, COash Guard, Air Force,Army, Marine Corps and Navy.

--A-ccess to military curriculum materials isprovidedthrough a "Joint tcllemorandurn, of'Undo landing" betyyeen the U.S. Office ofEducation and the Department of Defense.

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What MaterialsAre Available?

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One'hunAred twenty 'courses on microfiche. (thirteen in paper form) and descriptions of

1) -I each have been provided to.the vocationalCurriculum Coordination Centers aq other'instructional materibls agencies for dissemi-nation.

Course materials include programmedinstruction, curriculum 'Outlines, instructorguides, student workbooks and technicalmanuals.

The 120 -courses represent, he fokwingsixeeen'vocational Subject areas:

Thacquired Materials are reviewed by staffand subject matter specialists, and Coursesdeemed, applicable to vocational and tech-,riical educaiio are selected for dissemination.

,The National Center for; Research inVocational Education is the U.S.. Office' of

Education's designated .representative toacquire the materials and.conduct the piojectactivities.

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Project Staff: 4 a

Wesley E. Budke; Ph.D, D7rectorNational 'Center learihghouse

Shirley A. Chase, Ph.D,Project director

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Agricultuie,AviationBuildingConstructionTrades.

ClericalOccupations

Communicationsaf tinv

ElectronicsEngine Mechanics

FoodoService,'ealthHeating & Air

V9onditioningachine ShopManagement &

Supervisii)nMeteorology &

NavigationPhotOgraphyPublic Service

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The number of courses and thesuljectoreasrepresentedoivill expand as additional mate-thils with .application to iocational andtechnical education are identified and selectsdfor dissemination.

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How Can TheseMaterials Be 'Obtained .

77`.:.:77";t -77 7.'"7.;

_ .Contact the Curriculum Coordination Centerinyour region for' information on obtainingmaterials (e.R., a4lability and cost). Theywill,respond to your request directly or referyou to an instructional materials agencycloser-to you.

TRALRebecca S. DouglassDirector100 North rirst StreetSpringfield, I L 627772174782-0759,

C0011D11.1/\1101.1eLNI-EfIS

MIDWESTRobert PattonDirector1515 West Sixth Ave.Stillwater, OK 74704405/377;2000

NORTHEASTJoseph F. Kelly, Ph.D.Director225 West State StreetTrenton, NJ 08625609/292.6562

NORTHWEST .; WiIl m Daniejls

DirectorBuilding 17Ai rdustrial_Par k

Olympia, WA 98504206/753.0879

SOUTHEASTJames F. Shill, Ph.D.DirectorMississippi State Unjversity

Drawer DXMississippi State, MS 397626Q1/3252510

WESTERNLawrence F. H. Zane, Ph.D.Director1716 University Ave.Honolulu. HI 96,822P8/948.7834

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bRA,INAGE- ..,, Correspondence Cowie

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.)0/eloped by:

United.States Army

Development andReview Dates

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Unknown

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Suggested BadcirOund-.

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Basic math skills plus algebra, and chart reading skills.

Target-Audiences:. ,

. Grades 10-adult -;. 4

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081curiatzonal Arse: - ''Building and ConstrUction .S

Cost:

$3.50

Print Pages.

173i

Availability:Military Curriculum Project, The Centerfor Vocational Educatron, 1960 KennyRd., Columbus. OH 43,210

Organization of Materials: '-

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-,-. Lesson objectifies, text readings, review exercises, answers,- supplementary charts and graphs, and course examines'

L.Type of If' ruction:

Ihdivi lized and self-paced

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..Type of Materials-

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Drainage 0. .

Lesson 1 Basic Drainage Principles

Lesson 2 Surface Runoff (Hasty and Rational Methods)

tiLesson 2A Surface Runoff (Talbot's and OCE Mods)

Lessdn 3 Design of Ditches and, Culverts-:-

Lessoil4 DrainageConstruction; Check Dams, DropInlets, Culverts and Ponding ,

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Lesson 5 1, :-- Subsurface Drainage

VIExamination ....

Supplementary Materials Required:

Annex A-r through A-6 and charts 1-3 provided .4

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No. of Pages: Average.0t

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Completion Tim.:

Flexible

36 Flexible

22 Flexible

/9 Flexible

27 Flexiblei A

12 Flexible

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Salmi es miaow tremor. Expires July 1, 1978

Course Description ,A

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This course provides basic information for the design of simple drainage Structures for roads and airfields. Some job skills included are

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Design and construct ditches and culvertsDesign subsurface drainage facilitiesDesign arKl use ponding areas , .

. \9. Design check dams and drot? inlets,.

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This course consists of five lessons each containing a lesson objective, readings, and reviti.g.i exercises on the following topics:1

Lesson 1 Basic Drainage Principles covers the importance of.clrainage, types and functions et drainage, structures for surface drainage,structures for subsurface damage, temporary drainage during construction, drainage maintenance, road drainagt, airfielddrainage, preliminary consideiations for drainage design, data required; ceconnaisance, general procedure in drainage design,design storm, gracirig, soil characteristics, frost action, uniform heave, differential heave, thawing, and sources of frost-action water. .

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Lessen 2 _Surface Runoff (Hasty and Rational Methods) is an introduction to runoff and describes the procedures for using the hastyand rational methods of calculating runoff. ti

Lesson 2A Surface Runoff (Talbot's and OCE Methods) provides the formula for u mg the Talbot and OCE Methods along with exampleproblems. ,

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I 6. . /Lesson 3 Design of Ditches and Culverts covers Manning's Formula for figuring design, construction equipment considerations, ulvert

design, size of pipe, flow and velocity.

Lesson 4 "Drainage Construction, Check Dams, Drop Inlets, Culverts, and Ponding is concerned with excavation of ditches with equipment,side ditches, errosion control, check dams, drop inlets, length and strength of culverts, strutting nestable corrugated metal pipe(CMP), headwalls and Wingwalls, reasons for pending, pending design assumptions, ponding specifications, volume, runoff curves,analysis of cumulative runoff curve, culvert types, culvert hydraulic-delign principles, and culvert design procedures.

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Lesson 5 Subsurface Drainage covers subsurfacrdramage criteria, drainage techniques, pipe laying criteria, vertical volls, filter materials,7.. preventing failures, and examples and steps in filter desi4ii. .if ( /,.

This course is designed for student self-stuch/ and,cin be used as'a sub-unit in envirolvnental control, construction, or some types of agriculture courser.,Eachiesson has an obtectwe, a coded text, exercises, and answers keyed to the text for student self-evaluation. A course examination of fifty multiple-choicequeltions is provided, but no answers are available. Supplementary charts and graphs are provided..,

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CI:Ilya IMO KVIKIVATOUt WIXOMa.

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Table of Contents

Basic Drainageyrinciples

Surface Runoff (Hasty and Rational Methods),

Surface Runoff (Talbot's and Oce Methods)

Design of 'Ditches and Culverts

Drainage Construction, Check Dams, Drop Inlets, Culvertsand Ponding

Subsurface Drainage

Answers to Review Exercises

Examinationao"

Graphs, Charts, and Tables

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ENGINEER 3OURSE 359-3SUB

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DRAINAGE

CORRESPONDENCE COURSE PR

U. S. ARMY ENGINEER SCHOOL

FORT BELV011t, VIRGINIA

This print' includes solution Change 1, Dated 31 July 74

EDITION 3 (J LY 1973)v

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INTRODUCTION

)&ore roads and airfields will be required"by our Armed Forces in future wars than'were required previously. The enemy's po-tential use of mass-destruction Weapons willrequire a greater dispersion of'our troops andequipment both in v6dth and depth. A vastnetwork of roads-aziotalrfields *ill be requiredto support these dispersed forces and to reas.,senible the' for concerted offensive action.

. Heavier aircraft and ground- willweapons wirequire, the construction of stronger roadsand airfields than, were needed in previous,ware.

A Major factor in constructing and main-taining "combat-ready" roads, airfields, 'andother installations its the control of surfaceand subsurface water. It has been said that

\a good wad_requires a tight roof and a dryCellar. Water leaking through the surfaceof a road or airfield can weaken these struc-tures from the top doslni. Failures from thissource may be eliminated by adequate crownand/or by good wearing courses or pave:meets. :' But even when a watertight surface .is provided, subsurtste water may enter thefoundation material and produce failure from----,the bottom. Foundation failuNt may beprevented by the proper use of materials andby the interception, collection, and disposalof the undesired watert

drainagecourse covers the design of simple

drainage structures for roads and airfields.It will teach you to use rainfall data in select-ing a design storm,- to design and 'constructditches and culverts, tp design-subsurfacedrainage facilities, to design -and use pondingareas, and to design check slams and dropinlets. The subcourse consists of six lessonsand 'an examination as follows:

Lesson 1. 'b.sic rainage Prindiples.

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'2. Surface Runoff (Hasty and Ra-tional Methods).

2A. Surface Runoff (Talbot's andOCE Methods).

3. Design of Ditches and' Ctrl-.verts.

4. -Drainage Construction, CheckDams, Drop Inlets, Culverts,and Pon-ding.

5. Subsurface Drainage. --

_Examination.

Eighteen credit hours are, allowed for thesubcourse.

You will not be limited as to the numberof hours you may spend on the subcourse,any lesson, or the examination.

Materials fu/nished:

Annex A-1 through A-6tables and graphsfrequently used are separately bound foryour convenience.

Charts 1, 2, and 3.

Tile format of this subcourse has beenchanged to facilitate student self-picing Etnd"to eliminate tthe necessity of submitting tothe USAES each lesson exercise for grading.Each lesson, in this subcourse is followed bya number of questions and exercises designedfor a review of that esson.. After completing

.study of the lesson, the student should answerthese' questions in the, space provided beloweach, then turn to the back of the subcoursebooklet where-the correaranswers have beenincluded. A comparison of the student an-swers with those, giiien in the back of thesubcourse will indicate the student's knowl-

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,En"edge and understanding' of the material pre-sented., When you have completed alt lessonsto your satisfaction, complete and forward

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the examination card which you will findin your sulacourse packet.

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CREDIT HOURS

TEXT ASSIGNMENT

MATERIALS REQUIRED

LESSON OBJECTIVE%

LESSON 1

BASIC DRAINAGE ,PRINCIPLES

Attached memorandum.

None.

To teach you the importance, of adequatedrainage, theater-of:-operations drainageconsideratioq.s, and how to use rainfalldata.

SUGGESTIONS Rcitl the atta hed memorandum throughrapidly to obtain a knowledge of its scope.Then read it through carefully, underliningthe_important points and objectives. Readthe review questions at the end of the les-son. 'Study the lesson, searching for an--sivers to-the review questions, and writeyour answers in the spates provided.Finally, check your answers'with the an-swers given for' this lesson at, the back of

. this booklet: Review as necessary.

ATTACHED MEMORANDUM

1-1. IMPORTANet OrpitAlkAGE

Drainage is enimportant considehtion in/ the planning, design, and construction of

military roads and airfields, both as to con-,fr struction and -use. The entire serviceability

of the road depends on the*adequacy of thedrainage system. The washout of a singleculvert may close the road to traffic at "acrucial time. The development of a soft spotmay lead to rutting and displacement and toeventual closing of the road for repairs.Properly designed and 'constructed drainagesystems are equally vital to the functioningof an airfield. It is most important thatadequate dralnage facilities be 'constructedto remove effectively any durface water from

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the runways and taxiways. One severe acci-dent resulting from inade4uate drainage mayoffset any, difference between the cost ofreasonably adequate and lef,a-than-adequate

- facilities. Adequate drainage, including theuse of pumping facilities of even a temporarynature, is of primary importance daring the,periodeof construction. _Inadequate drainageresult.* in high maintenance of constructionequipment and seriously interferes with theefficiency of both men and equipment. Thefirst construction work on -any project shouldprovidedrainage for the work to follow. Asconstruction progresses, every effort shouldbe made to complete the drainage system asplanned, in order to avoid any damage which

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might be caused by accumulations of mud,water, ice, and debris. Flooding caused' byinadequate drainage may lead, to failure ofroad and hirfield surfaces. Engineer officersand noncommissioned officers.should be fullyaware of the function drainage, includingadequate drainage during construction, andthe proper methods of providing it. Theimportance of drainage in road and airfielddesign and construction cannot be overem-phasized.

1-2. 'TYPES AND FU4CTIONS DRAINAGE

All drainage can be classified as surface orsubsurface. Classification depends on wheth-er the water on or below the surface ofthe ground at the point where it is first inter-cepted or collected for disposal,

a. Surface driina,ge. Surface drainageprovides for the collection and removal ofwater from the surface of roads, runways.taxiways, and hardstands. This is importantbecause water on tilt! surface interferes withtraffic, may cause erosion, and, if allowed toinfiltrate, can cause injury to the subgrade.Surface drainage also provides for the inter-

. ception, collection, and removal of surfacewater flowing toward road. and airfield sur-faces from adjacent-areas.

b. Subsurface drainage. Subsurfacedrainage is similar in some respects to sur-face drainage. Impervious strata may formwell-defined channels and reservoi for sub-surface water. Water is present &der thesurface 'because of infiltration of surfacewater. Surface water -seeps down throughopen or unsealed surfaces; or literally on topof impe4ious soil or rock layers. Accord-ingly, properly designedand maintained sur-faceWrainage systems should reduce the needfor spedal facilities for control and disposalof, ground water.\Ground water 'may pondabove imperyious strata to form a subsurfacelake (which is often called a perched watertable). Subsurface drainage is provided tointercept, collect, and remove any flow ofground water ,,into the subgrade; to lowerhigh water tablts;to drain water pockets orperched water tables; or'for any combination

of these purpojes. The employment of sub-surface drainage to prevent frost actiondamage is discussed later in this lesson.

1.3. STRUCTURES FOR SURFACE DRAINAGE

a. Crown or transverse slopes. Surfacewater is removed front road and airfieldpavements or wearing courses by providing,adequate ;crown or transverse slopes. Para-graphs 1-7 and 1-8 describe crown specifica-tions for roads and airfields respectively.

b. Open channels other than ditc es.

(1) Gutters. Gutters, or co binationcurbs. and gutters, are used to llect andcontrol surface runoff where open ditcheswould be 'hazardou or impractical. They aremost commonly employed along streets indensely settled areas, and along roadsthrough heavy cuts where the width of theroadway is limited.

(2) Dikes. Dikes Or intercepting em-bankments are used along shoulders on highfills, or along the tops of cutslopes, to collectrunoff. "Such runoff may be directed intoflumes. or into' natural drainage courses toprevent the erosion of unstable slopes.Flumes are installed on the surface of steepslopes to carry the accumulation of surfacewater to open ditches or to natural drainagechannels.

c. Ditchei. Ditches, alone or in com-bination with natural watercourses, providethe simplest as well as the .cheapest and mostefficient methodSthr handling surface water.The detailed design of ditches is covered inlesson 3. The following subparagraphs dis=cuss some factors to guide you in the use andlocation of ditches, as illustrated in figure 1-1.

(1) Diversion ditches. At every op-portunity rainage water should be diyertedor discharged from collecting channels or sideditches into, natural or artificial channels andcarried away from the site. This diversibnkeeps side ditches and channels reasonable insize, and reduces the seepage from the ditchesinto thee subgrade.

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*, Fignire 1-1. gtrectures for surface drainage.

Intirceptiork-ditehes. Much of thesurface water originating on adjacent areaswhich slope toward a .6o1 uction site canbe intercepted and carried off in interceptorditches before it reaches the site. Intercept-ing the surface water reduces the volume offlow into drainage facilities within the oper-ating areas and prevents drainage structuresfrom reaching uneconomical sites. Withoutinterceptor ditches, all of the water from ahill would Sow -along the inside or cht-side'titch. The pipe necessary to provide for thegradual increase of flow,would be excessivein size and very expensive.

(3) Plating 'of ditches along fills. Insome cases, drainage. ditches must be con-stricted parallel to the edge of a. fill.1,When

this is necessary, the ditch should be duginto the natural ground. The fill-ground-lineintersection should not be used as the bottomof the ditch because surface water would tendto infiltrate and weaken the fill. A bermshould lie placed between the toe of the filland the ditch when the fill is over 4 feet hiFigure 1-2 illustrates both the correct and theincorrect method for. locating a ,ditch parallelto a fill.

d. Storm drains.,In permanent construc-tion, storm drains are frequently used becauseproperty values will..not permit large surfaceditches, particularly for disposal of collectedrunoff. Storm drains are seldom justified fortheater- of-operations construction because itis more economical to use open ditches. When

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INCORRECTLOCATION

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,CORRECT lawLOCATION

NATURAL CaOUND LINE

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CORRECTLOCATION

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.NATURAL GROUND LINE

MORE THAN 4ft FILL

NATURAL. GROUND LINE

Figiire 1t2. Conatructibn of ditches, parallel to fills.

space is restricted, or the natural slope rif,theground is unsuited for the use Of open chan-nels, it may be necessary to install stormdrains to provide for the disposal of surfaceswater. A storm-drainage system is very,dif-ferent from a sanitary layout. A sanftarysystem must gathei all sewage into one col-lecting system and carry it to a treatment ordisposal plant. Storm drains are best installedin small units, each unit diaining a, small area

and carrying the water to the neare,sttwatA.-course.

e. Culverts. Culverts are used underroads, taxiways, and, occasionally, under run-ways, to carry water that cannot be divertedeconomically fo natural drainage channels byother means. They differ from storm drainsin that they generally conform to the gradeand alinement of the open ditch, stream, or

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natural drainage course at inlet and outletends. additional information about culvertsand culvert design is,,cont.iined 4-lessons 3and 4.

1.-4. STRUCTURES FOR SUBSURFACE-DRAINAGE

In most cases, the presente of excess waterin the subgrade or base course reduces thestability of the pavement foundation, and in-creases damage from frost action. Subsur-face drainage removes this excess water bylowering the water table, by acceleratingwater flow, by providing.a ready outlet forslow-moving ground water, or by intercept-ing such water before it reaches the areasthat it could damage. Open 'channels, sub-drains, combination drains, and vertical wellsare used to control ground water. .

a. Open channels.% Subsurface drainagemay sometimes be accomplished by providingside ditches or making existing ,ditchesdeeper. Such -ditches or open channels oftenlower the water to a safe level and also inter-

.- cept seepage. Deep ditches are often imprac-tical and are hazardous and scioukl not belocated adjacent to a roadway or runway.The ability of open channels to collect andremove subsurface water depends .upon thenature of the subsurface toil, the location ofthe channel with respect to ,the pavement,and the availability a a suitable outlet forthe water collected.

b. Subdrains. Subdrains (also referredto as subsurface drains, subgrade .drains,and underdrains) rre underground' drainagelines or ducts used only to c011eet andpose of giounti wateir. Subdrains 'may beconstructed of porous concrete, perforatedclay pipe, or perforated corrugated metalpipe laid with closed joints, or unperforatedconcrete, clay or tile "pipe, laid with openjoints. These pipes should be enclosed in alayer of selected filter material. Blind drainsconstructed of crushed rock' or gravel of de-.sirable graduation, and drains improvised outof timber, -tire- other methods 'employed forsubsurface drainage.. Subdrains made ofpike, as well as blind or French drains, should

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be provided ',with ,free-ttowing outlets,' and,insofar as is practicable, should be construc-ted to® prevent ,backwater in *he drain. Amore conipiete. discussion of subsurfacedrainage is given in lesson 5. ,

c. Com bination drains. Undergrounddrainage. lines 'which combine subsurface an&surface' drainage are known as combined orcombination drains. Combination drains uSii-ally consist of a subdrain modified to per-mit the entrance of surface water. This isaccomplished by extending the filter materialsurrounding the drain to the ground surface,or near the surface, and covering with apervious soil layer. The installation of com-bination drains should be avoided, whenpossible, since they allow hifiltiation of sedi-ment and washing of soil from the trenchsides into the system. This usually leads tomore 'maintenance and repair work, on thepavement adjacent to the drain, and will re-quire the additional, work of cleaning the -drain pipe.

d . Vertical wells. Vertical wells aresceetimes constructed to permit trappedsubsurface water tQ pass through *an imper-vious soil or rock layer to a lower, freelydralning layer or soil.. If drainage is ob-,structal, additional wells are driven, or thepocket is drained with latriral subdrainsystem that is easily mitaind. Verticalwells are often used in northern latitudes,where deep freezing is common, to permitfast runoff from melig snow to get throughthe frozent soil 'and iflacha,pervious stratum.The bottoms of these wells are treated withcalcium chloride or a layer of hay to preventfreezing.

1-5. TEMPORARY DRAINAGE DURING. CONSTRUCTION

Proper consideration( of drainage duringthe construction period will frequently elimi-nate costly initial delaYs and future failuresdue- to saturated subgrades. A careful con-sideration of the following items will aid inmaintaining satisfactory drainage during theconstruction period.'

11:a. Diversion and outfall ditches. Drain-

,age necessary at the site to eliminate waterwhich would interfere with constructionoperations includes excavating diversionditches to concentrate all surface water, in -natural channels, and building outfall ditchesto -drain low or swampy -spots. Such workis an initial operation and may proceed atthe same time as clearing and grubbing.Careful consideration should also be givento the drainage of all constfuction roads,equipthent ,areas, borrow, pi d wasteareas.

b. Use*, of existing ditches and drainagefeatures. Miximum use of existing ditchesand drainage features shouldbe_made. Wherepossible, grading operatidfi should proceeddoWnhill, both for economical grading andto utilize natural drainage to the greatestextent. Backfilling,.existink ditches anddrainage channels should be so scheduled ageto permit the longest possible use of thesestructures for temporary, drainage

c. The use of temporary crowning. It isnecessary to maintain well-drained snbgradesiand base courses at every stage of construc-tion to prevent detrimental saturation. WhenWork is temporarily suspended a particulareffort should be made to remove runoff fromthe site. Cit and fill-sections must be crownedand high shoulders must be lowered.

d. Coordination of drainage plans. Con-.structiOn drainage plans should be coordi-nated with the layout and design of finaldrainage' facilities to insure maximum use oftemporary drains in constructing. pernianentfacilities.

1-6. DRAINAGE MAINTENANCE

The. drainage system must be maintainedso that it can function efficiently at all times.This goal can be obtained through adequatemaintenance inspections of . the structure's,

, _with` careful attention to removal of debrisand prevention of erosion,. Pei. ids of ,dryweather must be utilized in improving the(drainage system and correcting and preventing drainage failures. Any deficiencies in the

original-drainage-systems layoutMust be cor-rected asthey are discovered.,

a. Surface drainage. Defective or inadequate drainage is responsible for manypavement failures and much -deterioration.Ponding at. delayed runoff of surface water'allows seepage unless-the surface is tightlysealed. Areas are marked where inspectionafter rains reveals ponding surface water.Correction is made by or raising localdepression's, by providing additional culvertcapacity, and by providin outlets for waterobstructed by high shoulders. Penetration ofstorm waters through` pavement is controlledby sealing joints and cracks.

b. Ditches and drains. tlainage ditchesmust be kept clear of weeds, grtish, sediment,and other accumulation of debris that ob-itruct the flow of water. Ditches are main-tained as to line and grade, and sags andminor-washouts are corrected as they occur.Unnecessary blading or cutting, which de-stroys natural, ground cover, is avoided incleaning and shaping. Dense sod is developedto stabilize opezi ditches. Where vegetationis not effective &cause of soil or moistureconditiogs, erosion may be corrected by liningthe ditch with riprap or compac,ted bitumi-nous mix. Clogged _drains and culvert pipesare opened by cleaning out excess sediment:Culverts iirhieh have settled, heaved, or whichhave beerrpuihed out of line are repaired orreplaced.

c. Winter maintenance. Special atten-tion must be'give,n to drainage maintenanceduring thaws if there are accumulatien,s ofsnow., Side ditches are cleared of snow, andchannels are opened through snoVr-Incumu-lations on the shoulders to permit water toescape into the ditchesr-Every precaution istaken to prevent melt water from pondingon the runAyr.on the Shoulders, or in sideditches. Culverts and drffins are kept freeof ice and snow.

1-7. SPEC* CONSIDERATION' OR ROADDRAINAGE .

The basic objectives and requh'ements forsurface and subsurface drainage are covered

1 6

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19

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in ereviousy fparagraphs., 'A few% additional\it considerations. are presented here because of

their particular application to road drainage.

DrainakiFrof-road- surfaces: Surfacewater is. removed from the roadbed to keepit fromalenetrating the surfaee and wettingthe sfibgrade. Removal of this water is ac-complished by the introduction of a crownor of a transverse slope across the entire'roadbed width, or by superelevation on curves.The amount of slope provided by crowninggenerally depends upon the type of road sur-face. All smooth-surfaced roads are crownedbetween Y4 and Y2 inch per foot. Gravel- roadsand other rough, untreated surfaces require acrown of 3/2 to 3/4 inch Ni---foot:- In moun-tainous terrain, where sidehill cuts and fillsaresecessary, side:sloping is frequently usedinstead of crowning. This is done in orderto divert all surface water to the ditch on theinner, or cut, side of road, and thus pre-vent erosion on the outer, or fill, side. Super-elevation serves in place of crowning to takewater.from the surface of the road on curves.,

, Open-top culverts constructed of logs, timber,or rocks may be used on steep grades Whereheavy dm is a-I:meted down the road surface.They are placed at. an angle of about 60° to

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Figure 1-4. Log apen-t5, culvert.

the centerline or 30° to the perpendicular ofthe road. See-figures 1-3 and 14.

b. Side hitches. Water draining fromthe roadbed surface is collected into sideditches for disposal. These side ditches gen-erally serve to collect water from a consider-able area adjacent to the road., They shouldbe large enough to accommodate the runoff

_both from the roadbed and adjacent prea.s.;Side ditches are a potential danger to traffic.To reduce this danger to a minimum, theshoulders should be _constructed as wide asis practicable, with a minimum width of 4feet, and with a InAform slope toward theditch. If pobsible, the required cuss-sectionalarea should -be obtained by constructing abrtuad, shallow trapezoidal ditch. This typeof ditch has a large capacity. Its minimumdepth below the edge of the shouder shouldbe 11/2 Met. The mininium practical trap-ezoidal sedan is 11/2 feet deep and 2 feetwide at the bottom. Side slopes should not begreater than 11/2 to 1 in cohesive soil, and 3to 1 in sandy or loa,my soils. When possible,ditches should be deep enough to lower theground-water table under the road to below

1--7

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13the subgrade elevation, and thus perinitdrainage of the subgrade by seepage into theditch. Where it is economically possible todevelop and maintain turfed drainage chan-nels, the side slopes should not be steeperthan -4 . horizontal to 1 vertical to facilitatemowing and other operations incident tomaintenance. Ditches with comparativelyfiat side slopes must be protected by -rigidtraffic control against indlicriminate crossingby vehicles.

Ditch,relief culvert& On sidehill cutsor

_teriiherever roads intercept surface water

either in cut or fill, the water is drained, tothe fill side of the road bry. ditch-relief cul-verts. This is done to prevent ditches fromreaching uneconomical sizes o; dangerousdepths and to prevent erosion and saturation

'of subgradeshy the increasing volume of- water. On 8 percent grades, ditch-relief cul-

verts are spaced about 300 feet apart; on 5percent grades, 500 feet apart. Earth ditchblocks or headwalls are used to prevent thewater froze flowing past the culvert. In deepcuts it may be cheaper -and quicker to installculverts than to increase 'the width of theexcavation to provide space for wide sideditches.

d. $ubsuriaee drainage. Subsurfacedrainage is very rarely ,used,in military roadse*cept where it is expedient for special localconditions such as drainage base courses sub-ject to excessive saturation, draining groundwater encountered during construction, ordraining craters or frost boils during repairand maintenance operations. An effectivemethod to drain the base course is plenttrenches through the shoulder to the bottomof the' base course at approximately 150-footintervals on the low side of the sub ade,.and backfill with pervious material: Werethe longitudinal slope of the base is greaterthan its transverse slope, transverse ditches(approximately 1 foot in Width and to adepth of 1 foot below the bottom of the btsecourse) are excavated completely across thebase course and through the low s toulder.The ditches are backfilled with pervious ma-teriat, They should be placed at the low point

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of grades and at the 'meeting points of filland cut. s. '

1-8. SPECIAL CONSIDERATIONS FOR AIRFIELDDRAINOE.

Basic information applicable to drainageand drainage systems is contained in previ-ous paragraphs. A few additional considera-tions are prespted here because of their par-

,ticulai application to airfields.

a. Drainage of runway and taxiwaysurfaces. Provision must be made for posi-tive dispos%1 of surface water from runwayand taxiway surfaces by shaping the crosssection to shed, water to the side's. The maxi-mum permissible transverse slope for run-ways is normally 3 percent. For drainagepurposes, a minimum longitudinal grade of0.4 percent should be maintained. Maximumand minimum grades forsanways and taxi-ways are given in TM 5-330 and in pertinentAir Force publications. Sh4llow -difcheewith side slopes of from 4:1 to 10:1 may beconstructed, starting at the outer edge of 4the runway or taxiway shoulder. Deepditches p'roduce an operating hazard and, ifused, must be located from about 100 to 175feet from paved surfaces.

b. Effects of ,drainage on general de-sign. Proper grading is the most importantsingle factor contributing to the success of-the drainage system, and the grading anddrainage plans must be carefull coordinated.Although runways, taxiways, rdstands,and aprons must be laid out to confohn tocertain ,basic principles and specifications,care should- be taken in determining the ex-act location of these structures so as to facil-itate drainage as much-as possible. Airfieldlayout should be planned to take full advan-tage of topography in draining the site, to

,utilize the 'existing natural drainage system,and to avoid small.hard-to-drain areas. Theexact location of the runway may be governedby soil conditions, since subsurface water and

'drainage characteristics orthe soil, may varywidely between alternative runway locations.The two drainage factors affecting- the posi-tion of grade and centerlines are the she

1 8 '

21

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and size of structures required in naturaldrainage channels crossing the runway ortaxiway, and the height of the ground-watertable. Raising the raving grade may be nec-essary fq (1) obtain sufficient crown, or,transverse slope; (21 to provide a minimumof 1 foot between the ground-water table orcapillary water and the bottom of. the basecourse in soils where subgrade dratinage isimpractical; and (3) to maintain the re-quired minimum cover above drainage struc-tures. Drainage considerations, in conjunc-tion with soil conditions, also determinewhether or not the runway surfaCe must be!impervious.

C. Erosion control. Erosion control atan airfield site is not only required to keep

'.the drainage system effective- with a mini-mum of maintenance, but also to avoid pm:-Bible 'hazards to operations because of duatt_Seeding and planting open channels and dirtsurfaces 'prevents erosion and increases sta-bilization. Erosion control in nonuse areas ,may frequently be accomplished by terracing,in conjunction with a well-developed turfing'program. The terrace consists of a low,broad-based earth levee constructed approxi-mately parallel to the ground contours, anddesigned to intercept overland flow before itcan cause erosion, and, to conduct it to asuitable discharge point. TM 5-330,discussesthe design of terraces.

1-9. PRELIMINARY CONSIDERATIONS FORDRAINAGE DESIGN

a. Objective. The drainage system roustbe designed to remove, all surface waterfectively from operating areas, to interceptand dispose of surface water from adjoiningareas, and;to intercept and remove detrimen-tal ground water. The drainage systemshould, be designed to meet o rational rec,Tuirements with the selected esign storm

be dependent upon location, acility servedelocal conditions, and the like.

b. Type of installation. Considerationmust be given to the proposed u-se of theroad or airfield. If the road or airfield' is tobe used for only a short period of time, such

as one or two weeks, hasty design proce-dures would probably be used. However, ifimprovement or expansion is anticipatedafter the original operational requirementsare met, drainage should be designed so that 1any *future construction does not overloadditches, culverts, and, other drainage facili-ties. When all-weather operation is required,the drainage problems are more difficultif thelad or airfield is to be used only ding certain periods.

c. Engineer resources. The availabilityof engineer resources is an important pre-liminary consideration. Heavy equipment,such as dozers, graders, scrapers, and noWershovels, is commonly used on drainage proj-ects. Where unskilled labor is available inlarge quantities, together with the necessaryhand tools, much work can be done by hand.Provision must be made for the proper useof all available materials necessary for cul-verts, ditch lining, bridges, drains, and re-taining walls.

1-10. BASIC INFORMATION AND DATAREQUIRED

Before any design can be undertaken, cer-tain basic information must be available. Theamount required, of course, varies with thecomplexity of the design.

a. ' Topographic data. the best availabletopographic map should be utilized for lay-ing out drainage facilities because the topog-raphy greatly influences ale rate of runoff,and largely determines the number and sizeof the drainage structures required to draina given area. Contour maps or aerial photo -,graphs of the road or airfield site and theland adjacent to it should show all naturalwatercourses. If possible, contributing areasshould be defined or their areas indicated onthe Jargest-scale map that can be obtained.

b. Precipitation data. Because the max-imum rate at which rain falls is one of themost important factors to be estimated 'asa basis for drainage design, all ,podsible rain-fall data, such as frequency, intensity, andduration of storms, should be considered to

1 -9

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1

aid in the determination, of,this rate. Ratesof precipitation vary conside ly between

fig 2-5, lesson 2, world isohy tal map) ; rain-fall data for the locality being considered is ofprimary importance in designing a drainagesystem that will insure prompt, removal ofsurface water and positive control of groundwater. Ordinarily the most intense rain-storms that occur in a located area areshort, intense storms such as thunderstorms.It is common practice to design storm drainsto provide for disposal of runoff from rain-fall having certain average recurrence inter-Val's or'frequency of occurrence.intensity, corresponding to a parti ar fre-q uency of occurrence varies appreciably withthe duration of the rainfall, the average fatefor a period of 5 'minutes usually being sev-eral times higher than the average for aperiod of -1 hour. A study of rainfall inten-sity-frequency data for large number ofweather stations'indi tes that there arefairly consistent 'onships between theaverage in' tensity of rainfall for a period of

,1 hour and the average rates of comparablefrequency for shorter intervals, regardless;of the geographical location of the stationsor frequency Of 1-hour rainfall Consequentlystandard curves may be developed to expressthe rainfall "intensity-duration" relation-ships, with an accuracy satisfactory for road.and aiiiipld drainage problemi (fig 1-5) .

C. -Infdtratiloi. The term infiltration re-fers to the..absorption of, rainfall' by -tp,hground during a rain storm. The infiltrationcapacity: or 4bility of a soil to absorb pre:cipitation, normally decreases as the duratioilof rainfall increases, until a fairly definiteabsorption rate, is reached. Variations in,thestate of compaction, soil-moisture deficienbiesat the beginning of rainfall, and the elevationof the ground-water table, may greatly in-fluence the infaltratiOn capacity of a partid-,uiar soil.

d. Temperature and frost data. Tem-perate and frost data, with particular at-tention to maximum depth of frcIlt penetra-tion, should be ascertained.

e. Soil and ground - water. data. Soil andground-water data should be obtained from,a soil survey.

f. Other data. The necessary charts,graphs, and' tables for the design of the vari-ous types and° sizes of culvert constructionmaterials should be procured.

1-n. -DRAINAGE RECONNAISSANCE

A ground reconnaissance should providemuch additional information beyond thatmentioned in the preceding paragraph. SUcha reconnaissance is 'desirable because manyconditions that affect , drainage can be ob-served only by visiting the site. IrC manyplaces, gullies and other drainage ''paths in-dicate the effects of prerious rainfall. Pud.dies, soggy earth, and aquatic-plant growthall indicate that, for at least a portion of theyear, the natural drainage is inadequate forconstruction work, Dry and cracked earthis a sign. Of loss of Water througA evaporationand may indicate an,iMpervious subsoil andinadequate subsuiface drainage. Adjacent,streams should be studied, to determine -theprobability of floods and to determine, thedrainage outfall elevation. Similarly, incoastal areas, the elevation of high tideshould be noted to determine the drainageoutfall elevation and possible overflow.Springs, quicksand, seepage from steepbanks, and other indicators of high ground-water levels should be looked for. The type,density, and extent of surface cover sho'uldbe noted, since he presence or 'absence ofvegetation greatly influences runoff ciatrac-teristics of the area.

1-12. GENERAL PROCEDURE IN PRAINAGEDESIGN ......--

Pieliminary consideration of . the type ofinstallation-required, the engineer resourcesavailable, and the amount and reliability ofthe data collected determines the degree ofdesign necessary. The following steps are es-sential in the design procedure.

a. A very close study of a topographicmap is made to identify the areas that mar

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contribute surface or subsurface no* to theconstruction site. .The directions of all natu-ral.and subsurface flow, to and from the fete,are determined. If ground reconnaissancehas not been made previously,- one should bemade to confirm this map study.

b. fie proposed construction is thenlaid out on the largest-scale map or aerialphotograph obtainable. Special attention isgiven to the utilization of natural drainagechannels.

C. In the case of rods, a proposedgrade and ground profile is then prepared.In the case of airfields, a working drainagedrawing is made showing the layout and thetentative finished grading by means of con-tours. Drainage areas are ,outlined on 'themap, and their size obtained by scaling orplanimetering.

d. The design diticharge from eachdrainage area is determined, as'. described inlesson 2. Required sizes of channels, pipes,and culverts at critical points in the drainagesystem are then determined as outlined inthe same lesson. Frequently, it will be neces-sary to make several drainage layoutS beforethe most -economical system, with a properbalance between grading, surface drainage,and subsurface drainage, can be selected.

1-13. DESIGN STORM

The design storm is that sto1; which maybe expected to be equaled or exceeded on anaverage of one time during the design period.

a. The term "dekign-storm criteria" re-fers to the rainfall intensity-duration curveadopted as a basis of design for determiningthe capacity of drainage facilities for a par-ticular area. The rainfall intensity-durationcurves represent average rates of rainfall forvarious durationi that have the same 11.,,veragefrequency of occurrence. Such intensity-du-ration curves are computed from data for anumber of storms; consequently, all of theintensities repreSented by a particular curvemay not be expected in the same dormatleast not with the frequency indicated.

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b. Drainage fof military constructionshould be based on a 2-year design stormfrequency, unless exceptional circumstancerequire greater protection.

c. The rainfall intensity-duration valuerequired to produce the maximum drain-inletdischarge corresponding to a given, designstorm criterion, taking into consideration alldrainage area characteristics and pondingeffects, is referred to as the "design storm-rainfall". To simplify the preparation ofgeneralized diagrams for estimating drain-inlet capacities required under various con-ditions for design storm runoff, rainfall- isassumed to follow the standard rainfall-duration curve shown in figure 1-5.

d. The design-storm frequency servesas an index to the average frequehcy withwhich some portions or all of the storm-drainsystem will be taxed to capacity. The selec-tion of the design storm frequency for aparticialar project must be based primarilyupon judgment, with consideration of the pur-pose and importance of the given road orairfleld and such economic and engineeringlimitations as may exiSt. The duration ofrainfall required to produce the maximumrate of runoff will depend primarily upon thelength of overland flow, taking into accountsurface detention, roughness factor, andother surface -runoff characteristics.

e. The design -storm frequency alone isnot a reliable criterion of the adequacy ofstorm-drain facilities. In many instances,storms appreciably more severe than the de-sign storm may cause very little damage orinconvenience, whereas, in other cases, flood-ing of important areas may result. It is geri-,erally advisable to investigate the probable'consequences of storms more severe and lessfrequent then the design storm, before mak-,ing a final decision regarding the adequacy'of drain-inlet capacities.

1-14. CONSIDERATIONS FOR SUBSURFACEDRAINAGE

One of the first considerations of the engi-neering officer should be the selection of a

1-12

25

construction site which eliminates or mini-mizes the -need for surface and subsurfacedrainage. If it is impossible or impracticableto locate such a site, then one Of the mostimportant features of the design of a road-way or an airfield is the jroper incorporationof a subsurface drainage 'system in^the over-all plan. The Highway Research Board hasgiven the opinion that the majority of sur-face failures can be attributed to faulty, sub-surface drainage.. Although the pavementprotects theilbase to some extent from directinfiltration' of water, it is possible' for, waterto reach the base indirectly from less pro-tected surface areas. It is the purpose of' awell-designed drainage system to 'interceptthis flow of water before it ,reaches a partic-ular area, or to lower the' water table, oncethe water .has infiltrated into the soil.

1-15. RELATIONSHIP TO GRADING1

The pioblems relating to subsurface drain-age may best be handled when constructionoperations °ea road or airfield are initiated.because grading operations necessary forgood drainage may be combined with gradingoperations necessary fdr the primary con-struction. The importance of the relationshipof proper grading to good drainage cannotbe overemphasized.

r

1-16. SOIL CHARACTERISTICS

The degree td' which drainage becomes aproblem depends to a large extent upon the

7' characteristics of the soil where the con-struction is undertaken. Soils may be dividedinto three general groups as to their drain-age characteristics:

,a. Well-draining. Well-draining soilssuch as clean sands or gravels, may be drain-ed by the d,use of a gravity system. In road'and airfield construction open ditches may beused to intercept and carry away water thatcomes from the surrounding areas. In gen-eral, if the ground- ater table around thesite of a constructs project is controlledin these soils, it will be ontrolled udder thesite, also.

1

/8"b. Poor-draining. Poorly drained 'soils

include organic and inorganid fine sands andsilts and coarse-grained soils containing anexcess of nonplastic fines. In general, theflow of water in such soils is impeded by theircharacteristic density. It may be quite dif-ficult to lower the water table in such soilsby the use of a gravity system alone. In cer-tain cases, a system consisting of closelyspaced perforated-pipe drains may Prove ,ef-fective.. Another solution for.a drainage con-dition of this type is to replace the relatively.impervious soil with a pervious well-draining-type. This is- the best solution if the poor-draining soil is surrounded b9. a well -drainingsoil since this condition, if uncorrected, isvery conducive to ,differential frost heave.

c. Impervious soils. Impervious. soilsare fine-grained, homogenous, plastic toilsand coarse-gained soils containing plasticfines. Subsurface drainage is so slow in thesesoils that it is of little value in controllingtheir moisture content. Any drainage pro-cess in such soils may be difficult and expensive. The best means of securing adequatedrainage would be to replace,the impirvioussoil with ,a good pervious soil.

1:117. DESTRUCTIVE EFFECTS OF FRCI1 AC NIn certain climates where the air teapera-

ture may reach or go below the freezing'pointof water the combination of a high watertable and poorly drained soils may result infrost heave or frost boil. These usually havea very injurious effect on any wearing sur-face, the extent of which depends uponwhether uniform or differential heaving ot-.curs.

1-18. UNIFORM .HEAVE

Uniform frost heaving occurs if both thesoil characteristics and the paving characte -istics are the same over the area in questi n.It is necessary that conditions be , similarthroughout the area int order that the frelez-ing prkcess proceed un-Vformly. Although theground- level may disPlace upward, the dis-placement is the same over the entire area ;1-dee.'

26

1

hence no destructive cracks are caused byunequal displacement of adjoining sections.

1-19. DIFFERENTIAL HEAVE .

Differential frost heaving, on the ptheihand, occurs when Edson conditions are notuniform throughout the area, with the resultthat one section freezes and expands before,of to greater extent, than, an adjoiningsection does. Such differential movement canbreak up rigid pavements and cause seriousharm to flexible pavements when coupled

(with the. wing process. Figures 1-6 and1-7 show the differential frost heaveon rigid:aid flexible pa ements.

1-20. KINDS OF THAWING

When the subgrade starts to thaw, thedamage which results is dependent almostentirely upon the kind of thawing, since, de-

Figure-14i. Effect of frost heave on lgidpavement.

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pending upon weather conditions, thawingMay proceed in three ways:

. a. Thawing from the top down. Thisoccurs when the air teMperature suddenlyrises from below the freezing point to wellabove it and remains there .(or some time:This type of thawing causes aNifficult prob-lem because the frozen layer below the thaw-ing zone is impervious and represents a bar-rier through which the water corai5fromthe top cannot pass: Since, the soil beneaththe pavement is iii a supersaturated.state itprovides little support for the road surfaceand the repeated action of heavy wheel loadscauses deflection of the pavement thatplaces the soil particles and water directlybeneath the pavement. This is what is kiloas "pumping' and is pictured in figure 1If this continues, a- void is formed under thepavement and failure ultimately occurs bycracking of the surface. The problem is .particularly serious in soils of a silt or claynature since they are inherently unstable ifsaturated. The best method of prev,entingthis type of failure is to remove all silt andclay material in the, base and subgrade 'dur-ing construction and replace it with a goodpervious material, so that the water table islowered well below the base course.

1 14

1,..

Figure 1-7. 'Effect*Of frost heave on flexiblepavement.

27

4

I

Figure 1-8. Pavement subjected to pumping.

b. Thawing from the bottom up. Thaw-ing may also proceed from the bottom upin the event that the ai=r temperature risesto just below the freezing point and remainsthere for some time. In this event, the mate-rial closest to the surface will remain frozenwhile the deeper material will thaw as aresult of the transference of heat from the. interior of the earth. In the case of an air-field or in highway maintenance, this is ayery,desirable condition- since the water thatis released has a ready and convenient routedownward to the water table. If thawingproceeds in this manner,, there is little ten-dency for a reduction of subgrade stabilityto occur.

c. Thawing from both top and bOttom.When the air temperature remains barelyaboye the freezing point for"just tong enough,a.relatively trouble-free thawing processoccurs both from the top dovin and from thebottom up. The melt water resulting from thethawing of the bottom portions of the frozenlayer is disposed of as described in b above.The melt water resulting from the thawing

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of the top layers is not so excessive in quan-tity that surface runoff cannot handle it sat-isfactorily. 'Usually, much of the melt waterfrom the top is dissipated satisfactorily byevaporation into the air. Inc certain soils andunder certain conditions, however, thawingof this ,nature can produce a most difficultcondition, referred to as a frost boil. Whenthe air temperature remains barely abovefreezing for a prolonged period of time, thaw-ing from the bottom upward proceeds muchmore rapidly than from the top downward.While in most soils this would not be undesir-able, it can become so in plastic soils such asclays. The excess water developed by the,melting of the ice layers cannot be dissipatedby this soil rapidly enough, and a semiliquidittunstable mud layer develops. As long as thismud is trapped beneath a substantial frozenlayer, 'no 4ifficulty exists. But as the frozenlayer decreases in thickness it becomes 'toothin to bear traffic stresses and breaks inspots. The very unstable mud then oozesthrough the breaks. This supersaturated,semiliquid soil is incapable. of withstandingany appreciable load.

1-21. SOURCES OF FROST - ACTION WATER

There are three principal sources-of water(illustrated in fig 1-9) 'drat will prOyide anadequate supply for the frostzaction prAcess:

a. A high water table, which is 5 feetor less below the finished grade line.

,b. A capillary' supply from an adjoiningwater table. This is particularly a problem insilty soils which have a high capillary rate.Clays have a rather low capillary rate so thatfrost heaving is not as severe as in silts al-though thawing problems are greater than insilts.

c. A saturated condition of line- grainedsoils at or below the freezing stratum. Frostaction is uetially most severe in soils with ahigh moisture content.

1-15

PAVEMENT AND BASE

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DEPTH OF FREEZING AND: 7'GROUND WATER ELEVATION'

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rovides continuous supply of water despitebelow depth of freezing: Iriclined silt layer

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%WATER MOVES UPWARD,: *. . . WATER MOVES UPWARD.. .:.. .. - SATURATED FINE- GRAINED *SOIL !... . .

SATURATED FINE-GRAINED SOIL . 17.1,1Nr 0 mr .....A.....00t0t 0 ir I r-'01. .1,Z 11.0.0.0.0,110,41,4%,C3 0 C \ 0' , .. :::)CZ, CI C..7 - -, Q.PERVIOUS GRAVEL 0 I 0 ° GROUND-WATER ELIVATIOtIR:IC) - (...; c

Limited supply of wata0 moves upward from lower.portion ofsaturated fine- drained soil:

Figure 1-9. Sources of /water for the frost-action process.

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1-16

29

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REVIEW EXERCISES

Note: The following exercises are study 4. What .ia the principal aifferenae in theaids, The figures following each question re- layout of a storm-drainage system and a san-fer to a paragraph containing information itary system layout? (1-3d)related to the ,question. Write your answerin the space helow the que, ,t0n: When 'youhave finished answering all tre questions forthis lesson, compare your answers with thosegiven for, this lesson in beak of this booklet.Do not send hi your solutions to these reviewexercises.

1. When commending work on a' construc-tion project, whAt should be accomplished bythe first work that is done? (1-1)

4

4 .1

2. What factOr determines 'whether drain-age is to be classified as surface drainage orsubsurfacecitainage? (1-2)

3. Wheels the simplest, cheapest, and mostefficient method for handling surface water?(1-3c)

ns

Ao.

5. What are the four types of structuresmost commonly used in military constructionfor the control of ground water? (1-4)

6. When work on a road or airfield construc-tion project must be temporarily suspended,what action should be taken with regard todrainage? (1-5c)

7. How much crown is required ,in a gravelroad to insure runoff of surface water beforeit can penetrate and wet the subgrade?-(1-7a)

1 -17

*30

f.

8. What is the most important fattor whichwill contribute to the 'success of an .airfielddrainage system? (1-8b)

t7

9. Under what conditions would hasty de-sign procedures probably be used in the de-sign of a road or airfield? (1-9b)

10. What basic information, is considered tobe of primary importance hi designing adrainage systein that will insure prompt re-moval a surface :water and, positive controlof ground water? (1=10b)

'0

- 11. What are three variable conditions ofa particular soil which would influence thatsoil's capacity to absorb precipitation?(1-10c)

Is

12. If, on a ground reconnaissance you ob-serve an area of dry and cracked earth, whatwould this condition indicate tb you? (1-11).

13. What are the necessary considerationsin determining the degree of design necessaryfor a specific drainage system? (1-12)

14. Whitt is the definition of a design stormupon which the design for a drainage-systemis based? (1-13)

15. Under normal conditions, what is the de-sign storm frequency used for military con-struction? (1-13b)

1 -18

31

I

16. What are the priacipal factors,that de-termine the duration of rainfall required toproduce the maximum rate of runoff? (1-13d)

17. Duithag the process of constructing a 'road or airfield, what is the best time to take

"care of subsurface drainage problems? (1-15)

18. What is the characteristic of soils whichare made up of organic and inorganic finesands, silts, and coarse-grained soils contain-ing an excess of nonplastic fines, which is ofconcern in drainage? (1-16b)

219. What is the most likely effect that thitw-ing of subgrade from the top down mayhave upon a paved surface above that sub.!grade? (1-20a)

20. When the air temperatuie just above afrozen subgrade raises to Just below thefreezing point and - remains there for sometime, what happens to subgrade stability.?(1-20b)

1 19

3,2

1

4

LESSON

SURFACE RUNOFF (Hasty' and Rational Methods)

CREDIT HOURS 4

TEXT ASSIGNMENT Attached memorandum.

MATERIALS REQUIRED __Annex A.

LESSON OBJECTIVE To teach yOr., how to calculate surface runoff.

SUGGESTIONS Read the attached memorandum throughrapidly to obtain a knowledge of its scope.Then read it through carefully, underliningthe'important points and/objectives. Readthe review questions at The end of the les-son. Study the lesson, searching for an-swers to the review questions, and writeyour answers in the spaces provided.Finally, check your answers with the an-swers given for this lesson at- the back ofthis booklet. Reviewas necessary. - .t

ATTACHED MEMORANDUM

Sectipn I. INTRODUCTION

in the field shoadd receive benefit of the mostexperienced and the best engineering.judg-ment available.

GENERAL

There are several methods that may beused to deterthe amount of runoff froma given area, and the size of drainage struc-ture(s) required. Method? range from hastyto &aerate. The method used will dependupon time available, importance of the struc-ture being protected, and the length of timeit will be used. This lesson will cover theHasty Method which is a rapid, field methodfor estimating the size of a drainage openingrequired, and the Rational Method which isa deliberate method used for calculating thequantity of runoff from a given area to cul-vert or other point of interest. The subjectof drainage is highly complicated, and issometimes controversial. Drainage problems

2-2. FACTORS 1NRUENCING RUNOFF

Before doing into the methods for calculat-ing requirements for drainage structures, itmay be well to consider some of the factorsinvolved, other than 'rainfall.

a.. There are many factors which a.ffectthe rate and quantity of surface runoff. Thesize, shape, and slope of the drainage area

-_are the most important.

b. The first ,step ix determining the sizepf a drainage area is an analysis of the flowpattern of the water in the general vicinity.

2

v3

u) ,From this analysis the actual area contribut-ing runoff to the drainage. outlet apparentand the outline of the drainage arrea can bedrawn.

c. The process of marking this drain-age area boundary or divide on a map isknown as delineation. Usually a divide willfollow ridges and high points on saddles. Theoutlining of a drainage area is best accom-plished on a topographical map which has ascale of 1 inch equals 200 feet (1:2400) orlarger, which shows the final proposedlayout d contours.

4. The size of Ain area affects runoff intwo ways. First, a. large area will have alonger period of time over which runoff willoccur, and the peak runoff rate will be lessper acre than for a smaller area, assumingthat the total;runoftifoer acre remains thesame. Secondly, the maximum intensity ofrainfall for a given frequency varies inverselywith the area covered by the storm, thuslowering the peak runoff.

e. The shape of a drainage area governsthe rate of runoff because it controls thelength of overland flow.

f. The average slope (S) of a drainagearea controls. the time (T) of overland; flow.As the average slope of an area increases, thetime of overland flow decreases, and the rateof runoff increases.

g. Areas are classified as either simpleareas or complex areas. A simple area has80 percent or more of its total area covered_by one type surface (turf, concrete, etc.). Acomplex area has two or more types of sur-face, but no one type of surface amounts toas much as 80 percent of the total area.,

h. The drainage area may be subdivideqby lines which separate overland flow repre-sentative of one portion of the area from theoverland flow representative of other portionsof the area. Areas thus delineated are knownas subareas.

I. When the outflow 'of an,. area, eithersimple or complex, contributes to the outflowof another area, either simple or complex, the

total outflow is considered as runoff from suc-cessive areas.

j. Distances are scaled from a ihaP,grading plan; or drainage-layout drawing,Slopes are estimated by methods, taught inbasic map reading. Exercises in this sub-course will be based upon the average slopefor the path of flow 'being investigated. If apoint is located betweektwo contours, esti-mate its elevation by interpolation. Deter-mine the difference in elevation between thetwo pointi, scale the distance of flow (D0F),and calculate the average slope. In determin-ing the slope of a ditch where culvert invertelevations are given, assume that a uniformditch slope exists between the culverts. The.invert elevation is the elevation of the lowestpoint of the inside 'perimeter at the end.tof theculvert.

k. A path of flow is the route that stir-face runoff will follow to the area outlet. Run-off will flow from higher elevation to lowerelevation in a direction perpendicular tathecontours. Generally there are so many possi -'ble paths of flow that it would 'be impracticalto consider all of them; therefore, paths offlow are selected on the basis of'being mostrepresentative in length and slope of all thepaths of flow occurring in the area or sub-area: The number'of representative paths offlow from the subareas should be selected inproportion to the size of the subarea with ,respect to the total area.

1. There are three general types of flowto be considered ; sheet flow, channelizedflow, and ditch flow. Sheet flow is water thatflows at a more or less equal depth in ablanket across a uniform or nearly uniformsurface such as a grassed field, surfaced road,runway, parlftg area, or roof. As 'a generalrule water begins to channelize or collect into'ditch -like flow when it flows across surfacesnot protected by paving or structures de-signed specifically for erosion prevention Suchas plowed contours and terraces. Except inthe cases wheie channelization is specificallyprevented, sheet flow should be expected tobecome.. channelized flow after a distance ofnot over 400 feet in very flat, smooth terrain

2 2

and much soDner in rough, steep terrain. Ifreconnaissance can not be made, 200 feet maybe used as an average length of °sheet flow.

m. The length, designated by the sym-bol "L", of sheet flow is the horizOntal dis-tance measured along the representative pathof sheet flow fr.= the area divide to the be-ginning of channelized flow or ditch flow.Channelized flow and ditch flow lengths arehorizontal distances measured along their re-spective paths_of flow.

/ n. Retardance, designated by the sym-bol "n", is the term used tb designateresistance to sheet, channelized, and ditRavi caused by various surface conditilmssuch as vegetation, surface, and alignmentin the path of flow. The factors that detersmine the "-n" for the different types of flow.

,*ter

z7are dissimilar, but available data indicatesthat the retardance values in tabl:a 2-1 areapproximately representative of most sur-faces encountered.

TABLE 2-1. Retardonce Coefficients.

Type of Surface nt,, Smooth Pavement , 0.02Ditches .0.02Compacted Gravel Surfaces 0.06care Surfaced 0.Channelized Flow from

Average Grass Cover 0.2Sparse Grass Cover 0.2Average Grass Cover 0.4Dense Grass Cover 0.8

t ...

Section II. THE HASTY METHOD4

2-3. HASTY METHOD OF DETERMININGRUNOFF .i.

Compute the cross-sectional area of the0. ditch or gully in which the culvert or drain-

age structure is to be, built, using the high-water mark to deterniine the height and theposition of the upper width. To find the cross-sectional areacrequired for the drainagestruc-ture, double the cross-sectional area of thechannel (fig 2-1).

Channel area(b1 + 1%)

h2

Structure area = 2 times channel area or

(131 + 1%) h; *ere

b1 = bottom width in feetI

b2 = upper width in feet

h = vertical distance between upper andlower width in feet

3

2-4. EXAMPLE

What is the required structure area for astream that has the following characteristics:width of stream bottom, 4 feet; depth at high-water mark, 3, feet; width at high-watermark, 6 feet.

Channel area = (4 + 6) x 3 = 15 sq ft2

Structure area = 2 x 15 = 30 sq ft ,a. From the above problem it can be

seen that a culvert installed at this point inthe stream must have a minimum, cross-sec-tional area of 30 sq ft.

b. This method does not directly take ..into account the size, shape, and slope of thearea, surface vegetation, condition of the soil,or rainfall intensity, but, instead, gpes to the-outlet conditions for the 'estimating factor.This hasty calculation is used only when timedoes not permit a more exact method.

0

3

HIGH WATER MARK

4

Figure 2-1. Ditch section.

Section III. THE RAT101)IAL METHOD

2.5. PURPOSE

The rational method is used to !determinethe runoff that can be expected froma givenarea. To use it effectively requires a atildy ofmany variables such as the terrain, slopes'Ssoil, Vegetation and the hydrology of thearea. It will be the purpose of this section todiscuss in detail, the rational method and its'variable parts, and the use of the method indetermining the runoff from different typesof drainage areas.

2.6. RATIONAL METHOD

a. The rational method utilizes the em-pirical equation:

Q = CIAwhere:

Q = Runoff from ,a given drainage areain cubic feet per second (cfs)

C = Coefficient representing the ratio ofrunoff to rainfall:-

I = Intensity of rainfall in inches perhour of the storm generating maxi-mum runoff.

A. = Drainage area in acres.

-Ar b. A-itmiptions for use. Before discus-sion of thelliquation and its variable parts,

the .following Basic assumptions must bestated:

(1) Entire drihlage area is contribut-ing to the runoff.

. (2). Rainfall intensity is maximumand 'equal over the drainage area. ,

(8) The area has a regUlar shape.

(4) The use of the method is limitedto areas not exceeding 3,000 acres.

(5) The area has homogeneous soiltype and vegetative cover. In the event thisis not so, further assumptions are made asfollciws:

(a) Simple area One type of soiland .cover predominates in 80% or more ofthe .area.

(b) Complex area One that iscomposed of two or more different soil types,cover, or man-made areas, no one of whichcorttitutes 80% or more of the area:

2-7. RUNOFF COEFFICIENT C

It-is known that when it rains some of therainfall is "lost" due to infiltration, evapore-tion;and interception. As a result of theselosses all of the rain fatting on a given areadoes not run off. The "C" value used in the

A

I

rational method expresses as a ratio the per-centage of rainfall that is expected to run offExpressed mathematically the value 'of "C1

is the ratio of runoff to rainfall orRunoff

a. Basic "C"-, value.

(1) The basic value of "C" is takenfrom table 2-2. Fr example, review of thetable shows that asphalt has a "C" value of.80 - .95. What is implied is that 80 - 95% ofthe rain that falls on an asphalt surface willrun off. From the type of material this iswhat would be expected. Consider the rain-fall runoff from . a beach sand. It is verysmall, if any, die to the-beach sand being apervious material. From table 2-2, it is foundthat the "C" value for a pervious soil is 0.01to 0.10. This means`that only 1 to 10% of therainfall on a pervious soil will run off andthat 90 to 99% will be lost. The loss is pri-marily due to infiltration.

(2) In table 2-2 there are onlygeneral tyres of soil listed, "pervious","slightly .pervious", and "impervious", eachgiven a "C" value range with and withoutcover. In order to correlate these basic soiltypes with soils defined and classified widerthe Unified Soil Classification System (USCS)table 2-3, w/lIth is an extract of a USCS,soilcharacteristics table, has been included here.The three general soil types as shown in table2.2 correspond, in drainage characteristics,to soils in table 2-3 as follows:

Pervious Excellent

Slightly pervious Fair to poorImpervious Poor to practically

impervious

A GW soil has excellent drainage character-istics, which means it is very porous. A GM.soil has poor to practically impervious char-acteristics, which means it is impervious.

Rainfall

(3) The values in table 2-2 for the dif-fering soil descriptions are specified with andwithout turf (vegetation). Note the differ-ence between the C values foi' a soil type withand without turf. The "with turf" C values

are lower, indicating more loss and less run-off. This is caused by the turf retarding theflow, and thereby allowing more time for thewater to infiltrate into the soil.'

(4) With reference to table 2-2 it willbe noted that for each type of Material theC, value has upper and lower limits. Judg-ment, achieved by field experience, will deter-mine the C value to use in the calculations.Until this experience is achieved it is recom-mended that the higher limit be used.

b. Corrected "C" value.

(1) In the use of table 2-2 if will benoted that asterisks () are placed after eachsurface type except woods and the man-madesurfaces. The footnote to table 2-2 requiresthat for these surfaces the "C" value be ad-justed for slopes greater than 2%. Expressedmathematically the correction is(Steerage 2) 0.01 + Canamcd = Ce,tedWhere: .

= Average slope of the areaConsumed = Table value at "C"

Ccomoteed "C" corrected for slope

The reason for the correction is that as theground slope increases the rainfall runoffwill flow at a faster rate over the ground sur-face. The effect of this speedup is to reducer:the time available for the water to infiltrateinto the soil. The reduction of this loss, dueto infiltration, will increase the amount ofrunoff, thereby increasing the ratio of runofgto rainfall. This in effect will cause an increasein the value of "C".

(2) The surface slopes within the areawill, as previously described, have an effectupon the value of C. Since the losses thatoccur take place over then entire area, it willbe necessary to determine an average sloperepresenting the entire area. In order thatthe average slope will be representative ofthe area, care should be taken to make cer-tain that the slopes selected will representapproximately equal areas. Since the losseffect is a function of surfaces, the slopes ofchannels or ditches are not to be considered.

2 5

30"TABLE 2-2. Surface Runoff Coefficients

TYPES OF SURFACE FACTOR (C)

-Asphalt pavements 0.80 to 0.95

Concrete pavements 0.70 4140,90

Gravel or macadam pavementN, 0.35 to Q.70

Impervious soils* 0.40 to 0.65

Impervious soils with turf* 0.30 to 0.55

Slightly pervious soils* 0.15 to 0.40

Slightly pervious soils with turf* 0.10 to 0.30

Pervious soils* 0.01 to 0.10

Wooded areas

(depending on surface slope and soil cover)0,01 to 0.20

*For slopes from 1 to 2 percent.

NOTE: The figures given are for comparatively level ground. Forslopes greater than. 2%, the factor should ipe increased by'0.01 fbr every 1 percent of slope, up to a maximum C of 1.0.

Use of "C" Value Table

Determine drainage ahlracteristics of soiltype(s).

2. Correlate terminology with terms used ih "C" value table(Terms correlated i paimgraph 2-7a(2)).

Locate the soil and/or cover type in the left column of table.i2-2. Read the highest value of the range listed in thecolumn at the right for that typeof soil and/or cover.

I. This is the "C".assumed value. For slopes greater than 2%4those values marked with an asterisk (*) must be corrected .using the followinirformula: --

(Saverage -2) 0.01 J. C assumed = Ccorrected

2 60

8

3,/TABLE 2=3. USCS Soil Characteristics (Extract)

MAJOR DIVISIONS(1) (2)

LETTER

(3)

i

DRAINAGE CHARACTERISTICS(11)

..

)

,

Coarse

Grained

Soils

.

.

...

.

Fine

Grained

Soils

,

1

Graveland

Gravelly-Soils.

GK., Excellent,

GP ExCellent

AI.

, 1d

'GMT\ 1\ 1u.

4 Fair to Poor

Poor to Practically Impervious

GC Poor to Practically Impervious

Sandand

SandySoils

SW Excellent .

SP

.

Excellent

1

4dSM 4

o

iu

Fair to Poor ' '''Poor to Practically Impervious

SC Poor to Pratically Impervious

Siltsand,

-Clays.'

LL4:50' ,

ML Fair to Poor

CLloco

Practically Impervious'

OL Poor

..

Siltsand

ClaysLL>5O

MH

.,.

.

Fair to Poorvr--""

Practically ImperviousCH

OH 4 Practically Impervious1

Highly Organic Soils.

Pt

L

,

Fair to Poor%.

3/c. Weighted "C" value.

(1) One of. the assumptions made inthe rational method is that there is homo-geneous soil type and cover throughout thearea. In many cases, the area will comprisecombinations of soil types and cover and eveninclude man-made structures. In these casesit would be impossible to determine a singlevalue of C to use in the rational equation. Itwill be necessary in such cases to use sometechnique to determine a C value to resentthe area To do this it must be determinedif the area is simple or complex. If one typeof cover and soil predominates in 80% ormore of the area it is a "simple" area and the"C" value tor that particular soil and/orcover type controls. In the event no one typeof cover or soil predominates in 80% of thearea, it is a complex area and the "C" valuemust be weighted. In this case a mathemati-cal proportion of the subareas and theirrespective "C" values must be made.

(2) It should be noted that before the"C" value is weighted the "C" value asst*nedfor each subarea must be corrected for slope.The correction for slope will be made if theaverage slope of the subarea is greater than2%.

(3) The weighting of the "C" valueis accomplished by multiplying the corrected"C" value by the subarea that is affected bythat, "Q" value, summing the products anddividing by the total area Expressed math-ematically the formula is:

r, Cati+ +4.C3A3--wczet.t

A2 +

.Furthermore if the area is considered com-plex, each subarea and its respective "C"value must be included in the weighting pro-cess. This I's done no matter what percentage'of the total area the subarea represents.

24. INTENSITY

a. Prior to the study of this paragraphit wdl be necessary to review the assumptionsmade in paragraph 2.8(b> of this lesson.

Also, paragraph 1-10, lesson 1, should' bereviewed for the intensity duration relation-ships of rainstorms.

(1) Using- the above 'referenced as-sumptions and intensity duration relation-ships developed, it Will be found that for agiven area only one particular storm will givea maximum discharge (Q). This particularstorm is the one that rains over the entirearea being drained for a period of time justlong enough for the runoff from all segmentsof the area to reach the outlet at the sametime. This time is called the area time ofconcentration, or TOC. A storm of shorterduration than this area'TOC would not lastlong enough for the runoff from the moredistant segments of the area to reach theoutlet together with runoff from segmentsnear the outlet. .Therefore, the runoff Nyopldnot be maximum. ,

(2) With reference to Figure 2-2 itwill be noted that all the area below the10-minute line will drain in 10 minutes orless. Runoff from the area between the 10and 20-minute line will reach the outlet innot less than 10 minutes but will have-drainedin not more than 20 minutes. Similarly therunoff from-the area betweearthe 20 and 30-

Zminute line will reach the 'skeet in not lessthan 20 nor more than 30 minutes. At theend of 30 minutes the entire area is draining;therefore the time of concentration (TOC).for this area is 30 minutes.

(3) Again referring to Figure 2.2, ifa storm of 20-minutes duration sweeps overthe area then two possibilities exist:

(a) The entire area was 'not wettedand therefore only a pottiorr of the area will,drain.

'(b) The entire area was wet, but,since the storm duration was only 20 minutes;all the area below the 20-minute line had ,drained through the outlet before the runofffrom thevarea between the 20 and 30-minute

, line had reached the outlet. The entire area,

2 8

O

4

I

4.4

Figure 2-2. Illustrative-"regular" drainage Brea.

therefore, is not contributing runoff to theoutlet at one time.

(4) For a storm duration of 30 min-`utes, then, the entire area is contribUting run-off' to the outlet at one time; for the runolfrom the closer areas has been replaced bymore rain. The area has now reached criticalflow, or-peak Q.

(5) AD storm whose duration is longerthan the area TOC will have a lesser intensity.Reference to the intensity duration curves inlesson 1 will show that as the duration of thestorms increase, the intensity decreases.From examination of the equation Q = CIA,it is obviotuithat as 'T' decreases the Q willdecrease..The critical storm then, is the stormwhose duration is equal to the TOC. '

b. Time of concentration (TOO).

-(1) Representatife flow.

(a) Based upon the discussion inb above, the area TOC must be determined.This is done by determining representativeflow paths. A flow path can be defined as thepath a raindrop will follow from 'the timeit reaches the ground until it reaches theoutlet. The flow path is called representativebecause it mild approximate runoff travelingfrom the majority of the urea until it reaches

- the outlet point. It is representative of thetime at which the majority of the area willbe contributing. runoff to the outlet point.Establishing representative flow pathstis

41

33based largely on extierience, judgment, and

(b).