February 1999 Water Supply Outlook - Belle Fourche and Cheyenne River Basins (7)

Belle Fourche and Cheyenne River Basins (7)
February 1999

Snow
As of February 1, the Belle Fourche basin is 82 percent of normal Snow Water Equivalent (88 percent of last year). See Basin summary of Snow Course Data at the beginning of this report for a detailed listing.

Precipitation
Precipitation, for the month of January was 175 percent of average in the Black Hills (186 percent of last January). Monthly percentages range from 18 to 233 percent. Year-to-date precipitation is 202 percent of average and 174 percent of last year's amount. Year to date percentages range from 185 to 228. This is from the 4 reporting stations.

Reservoir
Reservoir storage is above average in the basin. Angostura is currently storing 118 percent of average (116,100-acre feet). Belle Fourche reservoir is storing 165 percent of average (167,100-acre feet). Deerfield reservoir is storing 113 percent of average (14,500- acre feet). Keyhole reservoir is storing 180 percent of average (177,400-acre feet). Pactola reservoir is storing 113 percent of average (51,900-acre feet), and Shadehill reservoir is storing 113 percent of average (55,500-acre feet).

Streamflow
Black Hills water users should see above average runoff during the March through July forecast period. The 50 percent chance runoff for Castle Creek below Deerfield Dam is estimated to be 127 percent of average (6,200 acre feet). The 50 percent chance runoff for Rapid Creek below Pactola Dam should be about 26,500 acre feet (126 percent of average).

==================================================================================================================================
                                              BELLE FOURCHE & CHEYENNE RIVER BASINS
                                               Streamflow Forecasts - February 1, 1999
==================================================================================================================================
                                              |  <<====== Drier ======  Future Conditions  =======  Wetter =====>>  |             
                                              |                                                                     |
  Forecast Point                     Forecast |  ==================== Chance Of Exceeding * ======================  |
                                      Period  |    90%       70%    |  50% (Most Probable)  |      30%       10%    |  30-Yr Avg.
                                              | (1000AF)  (1000AF)  |   (1000AF)  (% AVG.)  |    (1000AF)  (1000AF) |    (1000AF)
====================================================================|=======================|=====================================
DEERFIELD Reservoir Inflow           MAR-JUL      3.22      5.00    |     6.20       127    |      7.40      9.18           4.90
                                                                    |                       |
PACTOLA Reservoir Inflow             MAR-JUL       8.7      19.3    |       27       126    |        34        44             21
                                                                    |                       |
==================================================================================================================================
                  BELLE FOURCHE & CHEYENNE RIVER BASINS                 |          BELLE FOURCHE & CHEYENNE RIVER BASINS
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 1, 1999
==================================================================================================================================
                                      Usable |  *** Usable Storage ***  |                            Number     This Year as % of
Reservoir                            Capacity|  This      Last          |   Watershed                  of       =================
                                             |  Year      Year     Avg  |                          Data Sites   Last Yr   Average
========================================================================|=========================================================
ANGOSTURA                              122.1    116.1    115.3     98.1 |   BELLE FOURCHE               7        88        82
                                                                        |
BELLE FOURCHE                          178.4    167.1    175.4    101.4 |
                                                                        |
DEERFIELD                               15.2     14.5     15.4     12.8 |
                                                                        |
KEYHOLE                                193.8    177.4    173.4     98.7 |
                                                                        |
PACTOLA                                 55.0     51.9     52.9     45.8 |
                                                                        |
SHADEHILL                               81.4     55.5     54.8     49.1 |
                                                                        |
==================================================================================================================================
 * 90%, 70%, 30%, and 10% chances of exceeding are the probabilities that the actual volume will exceed the volumes in the table.

The average is computed for the 1961-1990 base period.

(1) - The values listed under the 10% and 90% Chance of Exceeding are actually 5% and 95% exceedance levels.                  
(2) - The value is natural volume - actual volume may be affected by upstream water management.

To February 1999 Basin Outlook Report Contents Page

Belle Fourche and Cheyenne River Basins (7) February 1999

Belle Fourche and Cheyenne River Basins (7)
February 1999