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:
  1. groundwater exclusive (GWEX);
  2. groundwater commingled (GWCO);
  3. surface water exclusive (SWEX); and
  4. 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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