Device Mapper Udev Asm

8/11/2019 Device Mapper Udev Asm

http://slidepdf.com/reader/full/device-mapper-udev-asm 1/18

Optimal Storage Volumes for

Rainwater Catchment Systems in

Alaska

By

Greta Myerchin, Amy Tidwell, Bill Schnabel and

Daniel White

March 2008

ATTAC Research Report # 200801



TABLE OF CONTENTS

INTRODUCTION............................................................................................................. 1

Rainwater Catchment System and Storage Requirement ............................................... 1Objective ......................................................................................................................... 1

STORAGE RESERVOIR DESIGN ................................................................................ 2

2

23

Climate and Threshold Temperature .............................................................................. 3

3

4

44

5

6

7

8

9

10

Storage Reservoir Capacity.............................................................................................

Water Usage....................................................................................................................Roof Collection Area......................................................................................................

Precipitation Design Year...............................................................................................

PROCEDURE ...................................................................................................................

Community Selection......................................................................................................Optimization Protocol.....................................................................................................

RESULTS ..........................................................................................................................

SUMMARY .......................................................................................................................

REFERENCES..................................................................................................................

APPENDIX A: Design Year Climate Data for Selected Communities............................

APPENDIX B: Calculation of Current Storage Condition...............................................

APPENDIX C: Graphs of Optimal Rainwater Storage Volume for Twelve AlaskanLocations...........................................................................................................................

Optimal Storage Volumes for Rainwater Catchment Systems in Alaska

ATTAC: Alaska Training/Technical Assistance Centeri



INTRODUCTION

Rainwater Catchment System and Storage Requirement

Rainwater catchment systems are designed to capture and store rainwater for use as a

primary or supplemental water source. In residential homes, stored rainwater can be used

for landscape irrigation or household services such as toilets and laundry. Collected

rainwater may also be used as a source of potable water, although it is recommended that

the stored water be properly tested and/or treated prior to this use.

Design of rainwater catchment systems requires careful consideration of storage capacity.

Inappropriate sizing of a storage tank or reservoir can negatively affect a homeowner inmany ways. Overestimation of the storage requirement can result in an oversized and

needlessly expensive storage system. Undersized storage tanks, on the other hand, may

not fulfill the homeowner’s water use needs.

Objective

The objective of this report is to present computer modeling results intended to estimate

optimal rainwater catchment system storage requirements. The resultant optimal storage

volumes were calculated as a function of water demand, catchment area and local

climatic conditions for twelve Alaskan localities. The data are intended to serve as

storage basin design guidelines to be used during system planning. The guidelines are

intended to supplement, but not replace, the professional judgment of experienced system

designers with site-specific knowledge.

This reports describes the optimal storage capacity for systems designed to collect andstore rainwater during the operational season only (i.e., during non-frozen conditions).

Optimal storage volume is defined here as the minimum tank volume necessary to meet

water use demand through the operational season while maintaining a reserve capacity of

at least 5%.


ATTAC: Alaska Training/Technical Assistance Center1



STORAGE RESERVOIR DESIGN

A variety of factors influence storage requirements. In this study, factors relevant to

Alaskan rainwater catchment systems were considered. Such factors included catchment

surface area, collection efficiency, water use rates, and climatic characteristics.

Storage Reservoir Capacity

This study evaluated storage reservoirs with capacities ranging from 100 to 20,000

gallons. Storage tanks fabricated to hold volumes of 100 gallons or less are often used

for transport or as break tanks, but are not often used as primary rainwater storage tanks.

In regions of Alaska where freezing conditions persist, residential exterior tank sizes do

not commonly exceed 2,500 gallons, based on physical and insulation restrictions as well

as product availability (Greer, 2007). In circumstances requiring storage of large

volumes (i.e., greater than 2,500 gallons), interior or underground cisterns may be

utilized. Alternatively, captured rainwater can be routed to natural ponds or engineered

impound structures for storage.

Water Usage

An estimate of water demand was required in order to estimate the appropriate rainwater

reservoir volume. In practice, water demand varies from person to person and according

to lifestyle considerations. While water usage in most Alaskan households is similar to

average US household water use rates, a relatively large proportion of Alaskans reside in

limited water use households. Examples of limited use households include those without

flush toilets, clothes washers, or shower facilities. An estimate of twenty gallons per

capita per day (gpcd) is commonly used when households contain no flush toilet. If a

household contains a flush toilet, water use can increase to 70 gpcd (Johanson, 2002).

Other authors estimate the household water use for a typical family of four to range from

150 to 200 gpd (Siefert, 2004). This report presents results based upon assumed

household water use rates ranging from 5 gpd to 250 gpd.





Roof Collection Area

Rainwater catchment area was an additional model input parameter. In order to

effectively interpret the model results, a system designer must estimate the catchment

surface area of the system being designed. If the entire home roof surface is used forrainwater collection, this can be accomplished by calculating the horizontal surface area

under the roof, including the eaves. Reducing the estimated area by 10% will account for

loss by flushing, overflow, and other loss factors (Johanson, 2002).

Climate and Threshold Temperature

In this study, it was assumed that liquid precipitation was available for rainwater

catchment, but frozen precipitation (i.e., snow, sleet) was only available as spring

snowmelt. Additionally, it was assumed that the total volume of accumulated snow in the

catchment system was sufficient enough to fully recharge the storage reservoir upon

melting. Consequently, each modeled operational season began in the spring with a full

reservoir.

The modeled operational seasons in this report were bound by threshold periods, defined

as 15-day periods during which the average daily air temperature was above or below

specified threshold temperatures. As a result, the operational periods were considered to begin on Day 1 of the thaw threshold period, and end on Day 15 of the freeze-up

threshold period. In this study, the mean threshold temperature used for calculating thaw

was 0.1 oC, while the mean threshold temperature used for calculating freeze-up was -1.9

oC, based upon values recommended by Hinzman (1990).

Precipitation Design Year

The model output presented in this study was based upon typical precipitation patterns

experienced in specific Alaskan localities, as represented by the site-specific design year.

The design years represented actual climate data (e.g., precipitation patterns and thaw

season length) considered to most closely match average conditions for each site studied.

A table located in Appendix A provides further information with respect to the design

year characteristics of each modeled location.





PROCEDURE

Community Selection

Selection of the modeled communities was based upon population, climatic

characteristics, and location. Twelve relatively large regional hubs were selected in order

to represent a range of climatic characteristics experienced in various regions throughout

Alaska. The modeled communities included Anchorage, Barrow, Bethel, Delta Junction,

Dutch Harbor, Fairbanks, Juneau, Ketchikan, Kotzebue, Nome, Tok, and Valdez.

Descriptions of the climatic characteristics for each listed community are presented in

Appendix A.

Optimization Protocol

An automated evaluation process was devised to estimate the optimal storage volume

required for each community. The procedure was written in Visual Basic for

Applications and was implemented within Microsoft Excel software. The program first

determined a representative year for design purposes. This design year was selected from

a record of site-specific climate data, and represented the year most indicative of average

site conditions. Next, the program calculated individual tank profiles for a combination

of collection areas, usage rates, and storage capacities. The resultant tank profiles weregraphic representations of the daily water balance, as summarized in the following

equation:

Current Storage = Initial Storage + Precipitation Inflow – Water Consumed

Please see Appendix B for a more detailed description of the water balance calculations.

Storage optimization graphs, located in Appendix C, were prepared for each community

based upon the results of the water balance algorithm. From these graphs, users can

determine the estimated optimal rainwater storage volume under a given set of

conditions. As described previously, optimal storage capacity is defined as the volume of

storage necessary to meet the water use requirements at all times during the operational

season while maintaining a 5% reserve volume.





RESULTS

As described above, optimal storage reservoir volumes were estimated for twelve

Alaskan communities. The resultant estimated optimal volumes are presented in the

graphs in Appendix C. In order to obtain the optimal storage volume for a system under

consideration, the reader is asked to perform the following steps:

1) Identify the listed community with a climate most similar to that at the location of

the system being designed. Use the table presented in Appendix A and/or other

climate resources for this step. Use this community’s graph (Appendix C) for the

remainder of this procedure.

2) Estimate the anticipated water demand (gpd) and catchment surface area (ft2) for

the system under consideration, using recommendations provided in this report or

elsewhere.

3) On the appropriate community-specific graph, select the surface area curve

corresponding to the catchment surface area of the system under design. Identify

the point on that curve corresponding to the anticipated water demand listed on

the vertical axis.

4) The optimal reservoir volume is represented by the point on the horizontal axis

underlying the point at which the selected surface area curve meets the level of

anticipated water demand.





SUMMARY

Two-thirds of Alaska’s population is serviced by a public water supply, while the

remaining third utilize independent sources such as private wells or commercial delivery

(USGS, 2004). Rainwater collection is an alternative independent water supply practice

that can not only benefit households with little or no available water, but can also reduce

the demand on municipally-managed water resources. In order to aid in the design of

rainwater catchment systems statewide, this study was conducted to estimate optimal

rainwater storage requirements for a group of Alaskan communities experiencing a range

of climate conditions. Optimal rainwater storage volumes for twelve Alaskan locations

can be determined from the graphs in Appendix C.





REFERENCES

1. Greer Tank and Welding, Inc.; http://www.greertank.com/PolyTanks.htm (2007)

2. Hinzman, L.D.; The Interdependence of the Thermal and Hydrologic Processes of

an Arctic Watershed and their Response to Climate Change; (1990) University of

Alaska, Fairbanks.

3. Siefert, R. D.; Suggestions for Installing Domestic Water Storage Tanks; (2004)

University of Alaska, Fairbanks Cooperative Extension Service; Building in

Alaska Series; #HCM-04950.

4. Alaska Division of Community Advocacy (ADCA) website:

http://www.commerce.state.ak.us/dca/commdb/CF_COMDB.htm. Demographic

information for Ketchikan and Fairbanks.

5. Translators: Johanson N., Seifert R.D. Water Cistern Construction for Small

House; (2004) University of Alaska, Fairbanks Cooperative Extension Service;

Alaska Building Research Series; #HCM-01557. From a Norwegian publication:

BYGGFORSK, NBI A515.161



http://www.greertank.com/PolyTanks.htm

http://www.commerce.state.ak.us/dca/commdb/CF_COMDB.htm

http://www.commerce.state.ak.us/dca/commdb/CF_COMDB.htm

http://www.greertank.com/PolyTanks.htm



Appendix A

Design Year Climate Data for Selected Communities

Community

Design

Year

Available

Rainfall (inches)

Operational

Season Length

(days)

Operatioal

Season Begin

Date (Thaw)

Operational

Season End

Date

(Freezeup)

Anchorage 1977 11.3 212 26-Mar 24-Oct

Barrow 1986 2.6 107 5-Jun 20-Sep

Bethel 1978 11.0 171 11-Apr 29-Sep

Delta Junction 1960 8.8 172 14-Apr 3-Oct

Dutch Harbor 1997 54.7 338 1-Jan 5-Dec

Fairbanks 1978 6.9 179 4-Apr 30-Sep

Juneau 2001 45.0 270 20-Feb 17-Nov

Ketchikan 1952 147.4 333 31-Jan 29-Dec

Kotzebue 1977 6.1 153 4-May 4-Oct

Nome 1997 10.4 167 21-Apr 5-Oct

Tok 1985 6.7 172 17-Apr 6-Oct

Valdez 1976 46.3 243 27-Mar 25-Nov





Appendix B

Calculation of Current Storage Condition

The current storage on any given day was calculated according to the following equation:

,)1()1()1()( −−∗−+−= k U SAk Pk S k S where

S(k) = Current day stored water volume

S(k-1) = Previous day stored water volume

P(k-1) = Previous day precipitationSA = Rainwater catchment surface area

U(k-1) = Previous day water comsumption.

The equation quantified the available water at the start of any given day as a function of

the existing stored volume, the tank recharge, and water consumption. Two physical

constraints imposed on the modeled scenarios dictated that the total storage term could

neither be negative nor could it exceed a specified tank volume.

Please direct further inquiries regarding the modeling methods or results to the authors of

this study. They can be located at the University of Alaska Fairbanks Institute of

Northern Engineering, http://www.alaska.edu/uaf/cem/ine/.



http://www.alaska.edu/uaf/cem/ine/

http://www.alaska.edu/uaf/cem/ine/



Appendix C

Graphs of Optimal Rainwater Storage Volume for TwelveAlaskan Locations



Device Mapper Udev Asm

Documents

Transcript of Device Mapper Udev Asm