This spreadsheet illustrates the effects of pumping and recharge as they vary with time.  Similar concepts
have been applied in the eastern Snake River Plain that illustrate a "steady-state" response.  The "steady-state" response is identical to that presented in this spreadsheet if a continuous pumping or recharge activity were conducted for extremely long time periods (possibly greater than 100 years).  When aggregated into zones, the steady state responses may differ slightly, depending on how the average value for the zone was determined. The IDWR is determining zone averages weighted by the ground water irrigated acreage in a cell.  This spreadsheet does not employ any weighting, but merely takes the mean of responses for all model cells within a zone. For a description of these concepts see Response Functions.

It is emphasized that this spreadsheet tool:
 1) estimates hydrologic effects, not injury;
 2) provides only estimates, the model on which the estimates are based is inexact
 3) presents results on an average basis for relatively large zones and long river reaches.  It is not intended
    to be used to evaluate the effects of individual water uses on other individuals.

BASIS OF ESTIMATES
Hydrologic effects from ground water recharge and pumping are reflected in the changes in gains and losses of reaches of the Snake River that are hydraulically interconnected with the Snake River Plain aquifer.  Four reaches of the Snake River are represented as interconnected with the Snake River Plain aquifer in the SRPAM 1.1 model of the Snake River Plain aquifer (Cosgrove and Johnson, 1999) which was the basis of estimates presented in this spreadsheet. The four river reaches include: 1) the combination of the Snake River from Heise to Lewisville and the Henrys Fork of the Snake River below Ashton, 2) from the At Blackfoot gage to the Neeley gage, 3) from the Neeley gage to the gage Below Minidoka Dam, and 4) from the gage Below Milner Dam to Near King Hill.

The locations of ground water pumping and recharge are associated with predefined zones of the eastern Snake River Plain.  A single relationship is used to describe effects on river gains and losses for any location within a given zone.  That relationship is determined as the mean effect for all model cells within a zone.  The zone boundaries are shown in this figure.  Estimates are based on the concept of response functions.
 

USER INSTRUCTIONS
Several worksheets are included in this workbook.  Users need only enter data in the worksheet entitled
"Data Entry".  Data entry cells can be identified by their dark blue color.  All other cells contain text or formulas and cannot be overwritten. The data entry worksheet provides users with the opportunity to enter recharge and pumping rates for each four month period, starting in any year the user desires.  Estimates may be entered for future years to estimate effects of projected rates of pumping and recharge.  All input pumping and recharge should be in the units of acre-feet for each four month period.

The user may use the same, or different zones, to represent the location of recharge and discharge.  The zone identification numbers are specified by the user in row 9 of the "Data Entry" sheet.  Selection of the appropriate zone can be made by viewing the map.

Estimates of effects on spring discharge and river gains and losses are computed when the RUN button on
the "Data Entry" sheet is selected.  A brief delay will be encountered while computations are made.  Results are presented in a tabular format in the "Data Entry" sheet, and in graphical format on the "Graphs" sheet. Three lines are displayed on the graphs:  one representing only the estimated effects of consumptive pumping, a second representing only the effects of recharge, and a third representing the collective effects.

When fewer than ten years of data are entered, irregularities appear in graphs representing some river reaches. These irregularities are a result of numerical error when generating these small levels of impact with the numerical ground water flow model.  Only the general trend in these cases represents expected effects in the physical system.  When effects are very small the vertical scale on the graphs rounds to the nearest whole number creating the appearance of multiple increments with the same value.

The user is encouraged to use the spreadsheet to represent historical water use as well as experiment with
possible future uses.  The spreadsheet is intended to be a working tool that can help predict effects of various water use scenarios.

For further information, please contact:
Dr. Gary S. Johnson at johnson@if.uidaho.edu or Dr. Donna M. Cosgrove at cosgrove@if.uidaho.edu