January 1998 Water Supply Outlook - Belle Fourche and Cheyenne River Basins

Belle Fourche and Cheyenne River Basins (7)
January 1998

Snow.
As of January 1 the snow water equivalent (SWE) in the Black Hills has only reached 81 percent of average. Most of this snow came in late December. None of the sites in the basin are above 85 percent of average. Compared to last year the basin is just 45 percent of last year.

Precipitation.
Precipitation for the month of December was above average in the Black Hills by 26 percent. Of the 4 reporting sites in the basin Mallo was the highest at 191 percent of average for December. Ditch Creek was the lowest at 64 percent of average. Year-to-date precipitation is 121 percent of average and 59 percent of last years amount. Mallo has the highest year-to-date percentage of average (at 150 percent) and Ditch Creek has the lowest (at 67 percent).

Reservoir.
Reservoir storage is in good shape. Angostura is currently storing 117 percent of average (112,800 acre feet), Belle Fourche is 181 percent of average (164,100 acre feet), Deerfield is storing 124 percent of average (15,300 acre feet), Keyhole is storing 176 percent of average (173,100 acre feet), Pactola is storing 114 percent of average (52,400 acre feet), and Shadehill is storing 81 percent of average (41,200 acre feet).

Streamflow
Water users should see below average runoff for the Black Hills for the Mar- July period. Castle Creek is estimated to yield 61 percent of average flow (3,000 acre feet). Rapid Creek is at 57 percent of average (12,000 acre feet). Irrigation water shortage, in the basin, could be a problem this year.

==================================================================================================================================
                                              BELLE FOURCHE & CHEYENNE RIVER BASINS
                                               Streamflow Forecasts - January 1, 1998
==================================================================================================================================
                                              |  <<====== 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)
====================================================================|=======================|=====================================
CASTLE CREEK blw Deerfield Dam (2)   MAR-JUL      0.84      2.13    |     3.00        61    |      3.87      5.16           4.90
                                                                    |                       |
RAPID CREEK blw Pactola Dam (2)      MAR-JUL      -2.1       6.3    |     12.0        57    |      17.7        26             21
                                                                    |                       |
==================================================================================================================================
                  BELLE FOURCHE & CHEYENNE RIVER BASINS                 |          BELLE FOURCHE & CHEYENNE RIVER BASINS
             Reservoir Storage (1000 AF) - End of December              |        Watershed Snowpack Analysis - January 1, 1998
==================================================================================================================================
                                      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    112.8     89.4     96.4 |   BELLE FOURCHE               4        45        81
                                                                        |
BELLE FOURCHE                          178.4    164.1    136.6     90.6 |
                                                                        |
DEERFIELD                               15.2     15.3     15.4     12.3 |
                                                                        |
KEYHOLE                                193.8    173.1    141.8     98.2 |
                                                                        |
PACTOLA                                 55.0     52.4     54.2     45.8 |
                                                                        |
SHADEHILL                               81.4     41.2     44.1     50.7 |
                                                                        |
==================================================================================================================================
 * 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 January 1998 Basin Outlook Report Contents Page

Belle Fourche and Cheyenne River Basins (7) January 1998

Belle Fourche and Cheyenne River Basins (7)
January 1998