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Delta Island AgricultureDelta Island Agriculture

Technical Workshop onModeling Issues of the Delta

February 6, 2007

Jim Wilde, P.E.Delta Modeling SectionCalifornia Department of Water Resources

wildej@water.ca.gov

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Discussion TopicsDiscussion Topics

• Delta Island Consumptive Use (DICU)– Model description

• DICU model results– How does the model do?

• DICU uncertainties– What are the inherent model uncertainties

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DICU Model InputsDICU Model Inputs

• 142 subareasSome islands contain > 1 subarea

• 20 land use typesEach type is aggregated for each subarea

• 7 precipitation stationsDistributed by Thiessen Polygon method

• Constant seepage into low lands0.3 inches per foot of crop root depth per month

• Long term average crop consumptive useCU is then adjusted by pan evaporation

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DICU Model OutputsDICU Model Outputs

• Diversions– Water taken out of channels

• Seepage– Channel loss to the islands

• Drains– Return water pumped back

to channels

Monthly Average:Monthly Average:

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Ag Diversions and DrainsAg Diversions and Drains

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Impact of Ag Use in Dry PeriodsImpact of Ag Use in Dry Periods

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DICU Model UncertaintyDICU Model Uncertainty

• Irrigation– Fixed seasons for each crop– Schedule differs for critical and non-critical water year

types

• Monthly time step reduces variability– Stormwater runoff cannot be estimated

• Long term historic land use patterns not used– The land use is assumed constant– Double cropping not considered

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DICU Model UncertaintyDICU Model Uncertainty

• Leaching patterns are assumed the same every year– Applied as a post-processing step

• CU adjustment from one pan evaporation location– Uncertainty in spatial variability

• What are the farmers really doing?– Estimating local water management practices

can be challenging at best

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Now on to Delta AG Water Quality Now on to Delta AG Water Quality