Biological Systems Engineering Invent the Future …...Invent the Future VirginiaTech Biological...
Transcript of 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
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• 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
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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
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Outline
• Model 1: A Watershed Model We Trick Into Working in Ditched Systems
• Model 2: A Ditch Indexing Method
• Management of Agricultural Ditches
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Wrong flow directions and subbasins even with Lidar dem
Model 1.
Manokin River watershed, Princess Anne MD
SWAT-VSA
Wetness Index
Classes
10
1
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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.
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We know how much area is contributing and the volume of runoff…
…but from where in the landscape?
dQ/dPe = Af
Model 1.
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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.
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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
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Soluble P Loss kg ha-1
Kleinman et al. 2007 JSWC
Collick et al. 2014 Hydrol Proc
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Model 2. Indexing Ditches
Bucahnan et al., 2012 J Hydrol
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Rainfall Analysis
fi = mi /N
fi is the frequency of occurrencemi is the bin, N total rainfall events
Model 2.
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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.
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Travel Times
Three Phase Travel Time (i) storm runoff, (ii) shallow interflow, iii) ditches
Multi Directional (d-infinity) Routing
Model 2.
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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.
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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.
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ResultsModel 2.
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Channels• Which hydrologic
pathways are of concern from a pollution risk standpoint
• Which channels are good candidates for transport-specific conservation measures
Model 2.
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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
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• Ditch Filtration
• In-ditch biofilter
• Big hole• Filled with carbon
• Intercepts ditch flow, reduces N and P
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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)
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Influent
0.54 mg L-1
Phosphate
Lassiter et al. 2014 JEMA (In Review)
Bock et al. 2014 JEQ
43%
54%
41%
68%
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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
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Moses!!
Cut the
BS
and take
your
bath
Ditch Humor…Sorry