development of drain-warmf model to simulate water flow & nitrogen transport from an...

Development of DRAIN-WARMF Model to Simulate Water Flow & Nitrogen

Transport From an Agricultural Watershed:“Subsurface Flow Component”

Shadi DayyaniShiv Prasher

Chandra MadramootooAli Madani

CSBE 2008 Annual International Meeting, July 14th

McGill University

Department of Bioresource Eng.

Main Goal:To develop and validate a model to quantify flow and nitrogen transport from an agricultural watershed

Objectives:Evaluate DRAINMOD & WARMF (surface flow) models individually for hydrology & nitrogen transport

Develop a new model (DRAIN-WARMF) linking WARMF & DRAINMOD models to:

Simulate water quantity and quality (Nitrogen) on a watershed scaleEvaluate impact of Best Management Practices (BMPs) in reducing pollution from the watershed

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Surface Flow: WARMF ModelWatershed Analysis Risk Management Framework

Watershed scale model developed by Systech Water Resources under sponsorship from Electric Power Research Institute (EPRI).

Links GIS, data, and a modeling system together in a graphical user interface (GUI).

The algorithms of WARMF were derived from many well established codes

Strong point: Surface flow componentWeak point: Subsurface flow component

WARMF Structure of WARMF

Organized into five linked modules:Engineering module is the dynamic, simulation model that drives WARMFData module provides time series input data (meteorological, point source) and calibration data Knowledge module is a utility to store important documents for the watershedConsensus & TMDL modules are roadmaps that provide guidance for stakeholders during the decision making process

Model Inputs Meteorological data

Daily values for precipitation, Min/Max temperature, Cloud cover, Dew point temperature, Air pressure, Wind speed

Sub-basin shape fileID, Area, Slop, Aspect

Land use shape fileStreams shape file

ID, Upstream sub-basin, Downstream River ID, River Length / Slope / Width / Depth, Min/Max Elevation

Model OutputsSurface flow

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Subsurface Flow: DRAINMOD

Field-scale computer simulation model developed by Dr. Skaggs in 1980

The model simulates:

Hydrology of poorly drained, high water table soils Nitrogen dynamics in the soil-water-plant system under different management practicesEffects of drainage and water management practices on water table depths, soil water regime and crop yields

DRAINMOD includes freezing, thawing, and snowmelt components

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Development of the Model (DRAIN-WARMF)

Flowchart of the DRAIN-WARMF modeling interface

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GIS (Geographic Information Systems)

Layers:Sub-basins

Drainage

Soil

Landuse

Nitrogen Application

DEM

Stream Network

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WARMF Output Processor / DRAINMOD Input File Creator

Inputs: Surface flow (each sub-basin)

Precipitation

Sub-basin layer

Outputs:(Depth of surface runoff)i

i = sub-basin’s ID

(Rainfall)i = Precipitation – (Depth of surface runoff)i

DRAINMOD Rainfall input files are created

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DRAINMOD Input File Creator1. Subdivides watershed into uniform cells

2. Derive DRAINMOD input parameters for each cell

Sub-basins (ID, Rainfall file)

Landuse (.cin file)

Soil (.sin, .mis, .wdv files; K value)

Drainage:drained / un-drained

Drainage coefficient

Drain depth / spacing

DEM (elevation)

3. Creates .gen & .prj files for each cell Store DRAINMOD input parameters for each cell and identify accompanying files (weather, cropping, soils, and hydrology)

Results in a full set of DRAINMOD input files for each cell in the watershed

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Run DRAINMOD/Output Processor

DRAINMOD simulations are run for all cells

The output processor:

Reads DRAINMOD output files (.plt)Subsurface flow depth & WTD

For drained cells, drain outflow is calculated by querying the subsurface flow depth from the .plt file for each cell

For un-drained cells, the value of WTD is taken from .plt file for each cell

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Subsurface Flow Calculator:Un-drained cells

Finds the receiving cell for each un-drained cell

Using DEM and WTDs calculated by DRAINMODCalculates the WTHcell = Elevationcell – WTDcell

Takes the ΔWTH (between the un-drained cell (a) and 8 neighbor cells)Find the Max (ΔWTH) Set the subsurface flow direction to the steepest down slope neighbor [Max (ΔWTH)]

cell “a” flows to cell 7

Calculates flow using Darcy’s law Between cell “a” and “7”

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84

5 76

1

a

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Subsurface Flow Calculator:Un-drained cells

`

a

7

D

x

L

HAreaKQ

..

Cell a

Cell # 7

ΔWTDWTDa

WTD7

Ha H7

Flow Direction

Impermeable Layer

D

D

WTDxHKQ

**. 7

AreaDarcy’s Law:

X= cell size

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Watershed Subsurface Flow Calculator2 ways:

Not routedResults from each cell are summed to provide the total subsurface drainage flow for the entire watershed

Routed Using stream network (Network Analysis in GIS)

─ Calculates each cell distance to watershed outlet through streams

─ Asks for average time of concentration & the longest path

─ Calculates “time delay” for each cell

─ If time delay > 1 day then delays the flow accordingly

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Study AreaSt. Esprit Watershed

A sub-watershed of L'Assomption River in Quebec

Located ~ 50 km northeast of Montreal

Consists of 18 sub-watersheds; covers an area of ~ 25 km2; agricultural land occupies 65% of the total area

In the L'Assomption river basin, significant portion of the pollutant load comes from agricultural sources (Quebec Ministry of Environment)

St. Esprit Watershed

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Preliminary Results (Flow Simulation)

Results “Not routed”:

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Daily total subsurface flow at outlet

Monthly total subsurface flow at outlet

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Preliminary ResultsResults “Routed”:

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Simulated Observed

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94

Feb

-94

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94

Jul-9

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-94

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bsu

rfac

e F

low

(m

m)

Observed (mm) Simulated (mm)

Daily total subsurface flow at outlet

Monthly total subsurface flow at outlet

Summary

A comprehensive evaluation of WARMF model in eastern Canada under cold condition

 A comprehensive evaluation of DRAINMOD in eastern Canada under cold condition considering both drainage flow and water table depth

Development of a new model, DRAIN-WARMF, to simulate water flow and nitrogen transport from an agricultural watershed

Future Work

A comprehensive evaluation of DRAIN-WARMF for water flow and nitrogen transport

Evaluation of several BMPs for improving water quality for a given region

Thank You!