Nebraska Data Entry
The yearly Nebraska RRCA model update consists of gathering and preparing data
for input into the two preprocessors, mknecanal and mknedat, and the
collection of reported municipal pumping volumes. The output from mknecanal
(*.rcc files) and mknedat (*.agw,*.asw, *.aco, *pmp, *rcg, AND *.rcs
files), and the municipal pumping array are then read in by the final
preprocessor, rrpp. Input for mknecanal are calculated cell-by-cell
values of canal seepage. Input for mknedat are irrigation volumes for each
of four irrigation categories. Groundwater recharge is computed by
mknedat, while mknecanal simply formats and renames the canal seepage
arrays.
A detailed description of Nebraska's methods of groundwater and surface water
calculations are found in Nebraska Irrigation Computations for the RRCA
Groundwater Model (RRCAIrrigCalcs.doc).
Canal Seepage
Canal seepage volumes for all canals are calculated as a portion of the
calculated losses. Losses are the measured diversions minus diversions into
other canals, reservoir storage changes, and field deliveries. The fraction of
the calculated losses attributed to seepage for all federal canals (Canals
800-811) is .82. The seepage portion of the losses for all other canals (Canals
812-826, private and state systems) is calculated as the calculated losses
minus .7 times the measured Class A pan evaporation. Canal seepage calculations
and relevant data are located in the spreadsheets in the subdirectories of the
'Canal Seepage' folder.
Groundwater and Surface Water Irrigation
Groundwater and surface water irrigation are proportioned amongst four
categories:
- groundwater exclusive (GWEX);
- groundwater commingled (GWCO);
- surface water exclusive (SWEX); and
- surface Water Commingled (SWCO).
The computation of irrigation volumes and the proportioning to the four
irrigation categories are performed in a series of Access databases and Excel
spreadsheets.
Groundwater
Electric power records are used to estimate NE groundwater irrigation volumes
for all Natural Resource Districts (NRDs) except the Upper Republican, where
actual metered volumes are used. This method is based on the assumption that
the hours of use will be the same, no matter what energy source is used. The
average hours of pumping (Kilowatt-hours/kilowatt demand) is obtained for each
power district, which is then multiplied by the pumping rate of each well to
obtain the volumes pumped. These volumes are then queried out of the database
to obtain the groundwater irrigation volumes on a county-by-county basis. The
Upper Republican metered database is in
Wellpumping\irrigation\URNRDInfo2003.xls, and the crude power record
company data for the in the seven subdirectories of
WellPumping\irrigation\PowerRecords. The shapefile, reppowerdist
is included in Wellpumping\irrigation\PowerRecords, which contains the
boundaries of the power company districts in the region. The list of active
wells is in ActiveWells2003.xls.
Surface Water
Surface water volumes are the actual deliveries to the fields. The county
volumes are queried out of ArcView shapefiles. Pertinent shapefiles and data
are found in the folder SurfWatDelivery.
Acres
Reported acres are used for all surface water and commingled lands. National
Agricultural Statistics Service (NASS) irrigated acres are used for the
distribution of irrigation to the GWEX category for all NRDs except the Upper
Republican. Certified acres are used for the Upper Republican; these data are
located in URNRDInfo2003.xls. The NASS data are located in the
NASS folder.
Irrigation Category Partitioning
To obtain cell-by-cell volumes of irrigation for the four categories, two GIS
distance functions are performed. Lands irrigated by wells that are within 800
feet of any surface water lands are placed into the GWCO category and any
surface water lands with portions lying within 800 feet of a groundwater well
are considered to be SWCO lands.
Final Cell-by-Cell Irrigation Volume Computation
Uniform county-specific depths of irrigation are calculated for each of the
four irrigation categories using the acres in each category, the sum
groundwater or surface water irrigation volumes, and the groundwater or surface
water 'f' factors. The 'f' factors, found in
WellPumping\Irrigation\F_Factors.xls are the ratios of commingled:exclusive
irrigation application for each, the groundwater and surface water categories.
The uniform county depths of irrigation are then multiplied by the number of
acres in each grid square pertaining to each grid cell to obtain the final
cell-by-cell volumes.
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