recharge on non-irrigated lands

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Recharge on Non-irrigated Lands

ESHMC

8 January 2008

B. Contor

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Outline

• Review of current calculations

• Recharge tool review

• PEST possibilities

• Possible alternate methods

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Current Calculation

• Recharge = non-linear function of precipitation

Transition precip = ( 1/NK)(1/(N-1))

If precip <= trans. precip. then

Rechg = K * PrecipN

else

Rech = recharge attrans precip+ (precip - trans precip)

3 sets of parameters,• Lava rock• Thin soil• Thick soil

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Current Calculation

• Accounts for processes of lower winter ET and snowmelt accumulation by calculating all winter recharge in Feb.– This will require some adjustment for

monthly stress periods– I think the adjustments are doable

7(stolen from DDW003)

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Current Calculation

• Soil type 4 represents withdrawals for wetlands, cities & dryfarms

• NIR rasters are calculated off-line, prior to running recharge tools.

• NIR rasters are inputs to GIS recharge tool

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• User hands GIS tool five things:– Raster of non-irr recharge for each stress

period– Map of irrigated lands– Map of model cells– soil-group map– starting multipliers for soil groups

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• GIS tool hands FORTRAN tool five things– total area in each cell– irrigated area in each cell– depth of NIR in each cell, for each stress

period– predominant soil type in each cell– multipliers

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.sol file

Soils

Source of data 1 - new data 0 - no data-1 - use previous data

Values1-4 - soil type-9999 - no value

(stolen from May Training)

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.nir file

Recharge on non-irrigated lands

Source of data 1 - new data 0 - no data-1 - use previous data

Non-irrigated rechargedepth (ft) for each grid cell

A -9999 value means a raster value was not available for the cell

(stolen from May Training)

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Multipliers

Pest can be set up to touch these (though we didn't do this last time)

1 multiplierfor each of4 soil groups

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• FORTRAN tool calculates non-irrigated area in each cell:

• For each stress period, FORTRAN tool calculates recharge on non-irrigated lands:

recharge = (non-irr. area) x (depth) x (multiplier)

non-irr. area = (total area) – (irrigated area)

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PEST Possibilities

• Use 4 existing multipliers to adjust NIR differently for each spatial dist. of cover type

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Everything up to this slidehas described the status quo.

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Everything from this slideforward talks about

possible modifications.

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PEST Possibilities

• Allow additional multipliers (chop cover types into regions)

• Write little PEST-touchable utility to do the calculations & generate the *.nir input for FORTRAN tool

• Modify FORTRAN tool to do the NIR calculations internally, with PEST-touchable hooks

Easy

Difficult

Moderate

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Changing NIR Algorithm

• If we keep status-quo Recharge Tool processing, we can change offline calc. of NIR at will

• If we have FORTRAN calculate NIR, we will be committed to a single calculation algorithm

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Alternate Algorithms

• USGS (Bauer & Vaccaro?)– physically-based calculation using soils, precip,

runoff equations, ET...• SVRP (Bartolino)

– daily soil water balance using ET and precip (Rick Allen has already done some of this for ESPA?)

• Langbein – empirical relationship from nationwide data

• Other?

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Alternate Algorithms - Concerns

• USGS (Bauer & Vaccaro?)

– Quantabytes of data– Bazillions of parameters– Long-term average recharge

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Alternate Algorithms - Concerns

• SVRP (Bartolino)

– Needs to be adjusted for snow accumulation and melting

– Needs adjustment for topographic concentration of runoff

– Sparse weather-station data for calculations

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Alternate Algorithms - Concerns

• Langbein

– Tends to give much lower results than other methods

– Total annual recharge

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Alternate Algorithms - Concerns

• Other?

– We have to find or invent the method– We have to agree on it

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Backup Slides

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Current Calculation

• Recharge = non-linear function of precipitation

(stolen from DDW-003)

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The NIR groups arebased on 7 non-irrigatedland-cover types

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Recharge on Non-irrigated Lands Relationship

• Average non-irrigated recharge for each model cell• Non-irrigated recharge is calculated for every cell but will only be used on non-irrigated lands• Grid cells where a raster value is not present are represented as -9999

Non-irrigated recharge GIS raster Grid cells

Amount of recharge depthfor each grid cell

(stolen from May Training)