Modeling Crop Water Demand and Root Zone Flow Processes at Regional

Scales in the Context of Integrated Hydrology

June 15 - 17, 2010International Groundwater Conference

San Francisco CaliforniaSan Francisco, California

Emin C. Dogrul, Ph.D., P.E.Tariq Kadir, Charles Brush and Francis Chung

C lif i D f W RCalifornia Department of Water Resources

IntroductionIntroduction

In developed watersheds, agricultural and urban water p gdemands as well as pumping and diversions to meet these demands can be the main driving forces on the hydrologic runoff processesp

Agricultural and urban water demands are integral parts of the hydrologic cycle; they are affected by the hydrologic state of the watershed whereas the hydrologic runoff processes are affected by pumping and diversions to meet these demands

F l i t di it i t id th For planning studies, it is necessary to consider the interaction between water demands and the hydrologic runoff processes

IntroductionIntroduction

California Department of Water Resources has been pdeveloping simulation tools to address the interaction between water demands and the hydrologic runoff processes

The Integrated Water Flow Model (IWFM) and its stand-alone root zone component, IWFM Demand Calculator (IDC), are products of this effort

IWFM and IDC are generic tools that can be applied to any watershed in the world

This talk concentrates on IDC

Modeling Land Surface and Root Zone PProcesses

Two types of models:yp

1. Root zone simulation models (AquaCrop, CropWat, CUP, SIMETAW) only simulate demands and flows in the root zone

2. Descriptive integrated hydrologic models (MODFLOW, H d G S h WEHY GSFLOW PRMS) i l tHydroGeoSphere, WEHY, GSFLOW, PRMS) simulate most of hydrologic cycle but stresses are pre-specified

The two modeling approaches need to be integrated to The two modeling approaches need to be integrated to simulate the runoff processes and water demands, and to match water supply and water demand

Hydrologic Cycle Component InteractionsHydrologic Cycle Component Interactions

Land Surface andRoot Zone

Stream Lake

Unsaturated Zone

Groundwater

Features of IDCFeatures of IDC

IDC operates on a computational grid (finite element or p p g (finite difference)

Each cell is divided into areas of non-ponded crops (number defined by the user), ponded crops (rice and refuges; rice is also divided among rice with flooded decomp, non-flooded decomp and no decomp; refuges are p, p p; gdivided into seasonal and permenant), urban, native and riparian vegetation

Water demand is calculated for non-ponded crops, rice and refuge lands as well as urban areas at each cell

Soil moisture is routed at each cell for each land-use type

Features of IDC (continued)Features of IDC (continued)

IDC addresses two types of balance equations: mass yp qbalance equation (has to be satisfied at all times) and the balance between water demand and supply (does not need to be satisfied at all times)to be satisfied at all times)

Schematic Representation of Flow ComponentsSchematic Representation of Flow Components

P = precipitation ET = evapotranspirationp ec p tat o e apot a sp at oAw = applied water Dr = drain from pondsRP = direct runoff D = deep percolationUU = re-useRf = net return flow

Soil Moisture Routing in IDCSoil Moisture Routing in IDC

Governing conservation equation (implicit scheme; all flow terms are computed at time step t+1):

t 1 t w r aP ft P R A R D D ET

where = soil moisture, [L]; P = precipitation, [L/T];RP = surface runoff from precipitation, [L/T];AW = applied water, [L/T];Rf = net return flow of applied water, [L/T];Dr = pond drainage, [L/T];D = deep percolation, [L/T];ET = actual evapotranspiration, [L/T];a = soil moisture change due to changing land use area, [L];a

t = time step length, [T];t = time step counter (dimensionless).

Agricultural Demand Computation in IDCAgricultural Demand Computation in IDC

Non-ponded crops: p pDuring an irrigation or pre-irrigation period, IDC checks if moisture content is below a user-specified threshold. If it is, it uses the governing conservation equation to compute Aw that will raise the g g q p wmoisture to field capacity:

t 1 t afc P R D ET

f ,ini

fc p potfc t t 1min

wR U

t t 1min

P R D ETt ifA 1 f f

0 if

t 1fc

tmin t 1

min

Agricultural Demand Computation in IDC ( ti d)(continued)

Ponded crops: pDuring an irrigation or flooded rice decomposition period, IDC computes Aw to maintain the pond depth at user-specified values:values:

t aT D sw p rpot fP

A P R K ET R D 0t

sw p rpot ft

Other Features of IDCOther Features of IDC

Simulation of re-use of agricultural tailwaterg

Simulation of regulated deficit irrigation

Ability to specify water demand (i e contractual demands) Ability to specify water demand (i.e. contractual demands) instead of computing it dynamically

Source code executables and documentation are available Source code, executables and documentation are available for download at IWFM web site (http://baydeltaoffice.water.ca.gov/modeling/hydrology/IWFM/)

Other Features of IDC (continued)Other Features of IDC (continued)

IDC can easily be linked to finite-element or finite-difference yhydrologic models as well as to reservoir operations models

Ag & Urban Demand

IDC

Surface ff

Diversions runoff

Pumping Recharge

STREAM MODULE

GW MODULE

LINKED MODEL

ExampleExample

2622 grid cellsg model area is 2805 km2

average cell area is 1.07 k 2km2

20 non-ponded crops (including fallow and idle ( glands), rice, refuges, urban lands and native vegetation

Example – SoilsExample Soils Example – Land-Use TypesExample Land Use Types

Example – Comparison to DSIWM Values(with Ksat = 0.01 m/sec at cells with rice)

With minimal effort and no calibration, IDC values are reasonably close to DSIWM values

ConclusionsConclusions

IDC

simulates irrigation and farm water management practices as well as root zone flow processes realistically

allows effective simulation of conjunctive water use in watershed scale when linked to an integrated hydrologic model

can be linked to other models (e.g. hydrologic models, i d l i ti d l ) ileconomic models, reservoir operations models) easily

allowing the user to address multiple issues encountered in water resources planning studies

Questions?

Example Computational GridExample Computational Grid

EvapotranspirationEvapotranspiration

Assumptions: 1.00 f fssu p o s

• p is taken as 0.5

• ETpot can be taken 0.75ETpot can be taken as ETc, ETcadj or whatever is specified by the

0.50

specified by the user

0.25

0.000.00 0.25 0.50 0.75 1.00