Biological Systems Engineering Invent the Future …...Invent the Future VirginiaTech Biological...

Invent the FutureBiological Systems EngineeringVirginiaTech

Invent the Future

Watershed Science and Engineering Group [email protected]

Lessons From Agricultural Ditches –Modeling and Management of

Agricultural Drainage

Zachary M. EastonDepartment of Biological Systems Engineering

Virginia Tech

Watershed Science and Engineering Group

Biological Systems EngineeringVirginiaTechInvent the Future

• Agricultural drainage is vital to crop production in many areas where soils are poorly drained

• Increased depth of aeration, warmer soil temps, improved trafficability, etc

• Much of the CBW utilize ditch networks for drainage

• Ag drainage management has historically focused on shedding water as fast as possible and not on management of drainage for environmental benefits

Background



Motivation• Most of our drainage management tools are

focused on Tile Drained systems (e.g., Drianmod)

• Little work has sought to develop predictive or assessment tools aimed at ditch systems

• As a result, we have sometimes dogmatically* developed control practices based on what works in other systems and not on prudent management of ditch drained systems

*dog.ma …, n. … 2. a specific tenet of doctrine authoritatively put forth: the dogma of the Assumption. -The Random House Dictionary



Outline

• Model 1: A Watershed Model We Trick Into Working in Ditched Systems

• Model 2: A Ditch Indexing Method

• Management of Agricultural Ditches



Wrong flow directions and subbasins even with Lidar dem

Model 1.

Manokin River watershed, Princess Anne MD

SWAT-VSA

Wetness Index

Classes

10

1



Runoff Analysis

Q = Pe2/(Pe+S)

Watershed

UnsaturatedSaturated

Af Q (streamflow or

“excess” water)

P

Af, As, σe = f(S,Pe)

Af = ∂Q/∂Pe

Af = 1-(S2/(Pe+S)2

As = 1-(S2/(σe+S)2

σe=S(√(1/(1-As))-1

σe2=0 σe1=0 Pe1Pe2

Easton et al., 2008. J. HydrolEaston et al. 2011. Hydrol Proc

Model 1.



We know how much area is contributing and the volume of runoff…

…but from where in the landscape?

dQ/dPe = Af

Model 1.



Distributing Runoff

τ10=f(AS)

τ 8=f(AS)

τ 6=f(AS)

τ 4=f(AS)

τ 2=f(AS)

High : 33.103500

Low : 3.520011

STI

33.10

3.52

Wetness Index

Classes10

1

Moisture storage distribution curve depicting relationship of available storage S to the fraction of watershed area contributing runoff (As).

Model 1.



Ditches 7 and 8

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

3/1/06 4/1/06 5/1/06 6/1/06 7/1/06 8/1/06 9/1/06 10/1/0611/1/0612/1/06 1/1/07 2/1/07 3/1/07 4/1/07 5/1/07

Discharge,(m

3s-1)

SWAT SWAT-VSA Flume8

0.000

0.002

0.004

0.006

0.008

0.010

0.012

3/1/06 4/1/065/1/06 6/1/067/1/068/1/06 9/1/0610/1/0611/1/0612/1/061/1/07 2/1/073/1/07 4/1/075/1/07

Discharge,(m

3s-1)

SWAT SWAT-VSA Flume7

0

0.002

0.004

0.006

0.008

0 0.002 0.004 0.006

Modeled(m

3s-1)

Measured(m3s-1)

SWAT-VSA

SWAT

0

0.005

0.01

0.015

0 0.005 0.01 0.015

Modeled(m

3s-1)

Measured(m3s-1)

SWAT-VSA

SWAT

Model 1.

NSE=0.49

NSE=0.42



Soluble P Loss kg ha-1

Kleinman et al. 2007 JSWC

Collick et al. 2014 Hydrol Proc



Model 2. Indexing Ditches

Bucahnan et al., 2012 J Hydrol



Rainfall Analysis

fi = mi /N

fi is the frequency of occurrencemi is the bin, N total rainfall events

Model 2.



S = 15 cm

In the CN equation we use paired rainfall (Pe) runoff (Q) data to solve for storage (S)

P from 1cm storm allocated to Ia

Runoff

Q= Pe2 /(Pe+S)2

Model 2.



Travel Times

Three Phase Travel Time (i) storm runoff, (ii) shallow interflow, iii) ditches

Multi Directional (d-infinity) Routing

Model 2.



i) Surface Runoff: Steady state kinematic wave approximation with Manning’s equation

)ß

n L( q =TT

0.3

0.60.60.4-

ki,t,R

ii) Interflow: Steady state flow through soil

e

Lat

I

n

K

L=TT

The cumulative travel times (CTT) to streams are the sum of each grid cell travel time along each flowpath

ii) Ditches: Manning’s equation and the continuity equation

6.0

67.05.0D

W

Q

n

L=TT

Model 2.



Indexing Approach

CTT =fi

TTR,I,Di=1

M

åæ

èçç

ö

ø÷÷

Landuse P kg/ha/yrForest 0.06Pasture 0.49Corn/Soybean 0.67Manured Cornfield 3.05Barnyard 3.05Ditch 0.49

X

Model 2.



ResultsModel 2.



Channels• Which hydrologic

pathways are of concern from a pollution risk standpoint

• Which channels are good candidates for transport-specific conservation measures

Model 2.



Management• Drainage/flow control structures

• Reduce peak flows in ditches

• Increase the contact with biologically, physically and chemically active surfaces

• Promote denitrification by increasing the anaerobic period

• Modify conventional ditch management practices

• Substitute mowing for mechanical scraping or reduce frequency

• Contact with biologically, physically and chemically active surfaces

• Reduced erosion and better bank stability >> less maintenance


Biological Systems EngineeringVirginiaTechInvent the Future Management

• Ditch Filtration

• In-ditch biofilter

• Big hole• Filled with carbon

• Intercepts ditch flow, reduces N and P



Thu Fri Sat Sun Mon

06

12

18

24

Feb 27 to March 4

Nitra

te-N

(m

g/L

)

Thu Fri Sat Sun Mon

06

12

18

24

Thu Fri Sat Sun Mon

06

12

18

24

Thu Fri Sat Sun Mon

06

12

18

24

Woodchips

Biochar

Lassiter et al. 2014 JEMA (In Review)



Influent

0.54 mg L-1

Phosphate

Lassiter et al. 2014 JEMA (In Review)

Bock et al. 2014 JEQ

43%

54%

41%

68%



Conclusions• “Corridor” role of Ag ditch network

• Ditches can drain a significant fraction of watershed area, increasing drainage density, and decreasing flow distance to channels

• Models are helpful to identify which channels are good candidates for transport-specific conservation measures

• Accurate representation of basin hydrography, including fine-scale artificial drainages, is critical to the accurate simulation of hydrologic response

• Important to consider whole system, ditch and contributing area

• Ditch management and In-Ditch Biofilters can reduce N and P export from ditch drained systems



Moses!!

Cut the

BS

and take

your

bath

Ditch Humor…Sorry

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