Belle Fourche and Cheyenne River Basins (7)
February 1998

Snow.
As of February 1, snow water equivalent (SWE) in the Black Hills was 87 percent of average. SWE at two sites, Mallo and Mount Tom, was slightly above average. Basin SWE is 52 percent of last year's amount. Measured snow depths ranged from 7 inches at Bearlodge Divide to 25 inches at Reuter Canyon. All the reporting sites are below last years figures at this time.

Precipitation.
Precipitation, for the month of January was 14 percent below average in the Black Hills. Of the 4 reporting sites in the basin, Warren Peak had the highest percentage of average for January (100 percent of average). Ditch Creek had the lowest percentage of average (75 percent of average). Year-to-date precipitation is 113 percent of average and 60 percent of last years amount. Mallo has the highest year-to-date percentage of average (at 133 percent) and Ditch Creek has the lowest (at 69 percent).

Reservoir.
Reservoir storage is in good shape. Angostura is currently storing 118 percent of average (115,300 acre feet), Belle Fourche is storing 173 percent of average (175,400 acre feet), Deerfield is storing 120 percent of average (15,400 acre feet), Keyhole is storing 176 percent of average (173,400 acre feet), Pactola is storing 116 percent of average (52,900 acre feet), and Shadehill is storing 82 percent of average (40,500 acre feet). Streamflow
Water users should see below average runoff for the Black Hills during the March- July period. Castle Creek is estimated to yield 70 percent of average (3,450 acre feet). Yields in the Rapid Creek drainage should be 14,500 acre feet (69 percent of average) for the March - July period. There could be irrigation water shortage in the basin this year. 
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                                              BELLE FOURCHE & CHEYENNE RIVER BASINS
                                               Streamflow Forecasts - February 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      1.97      2.85    |     3.45        70    |      4.05      4.93           4.90
                                                                    |                       |
==================================================================================================================================
                  BELLE FOURCHE & CHEYENNE RIVER BASINS                 |          BELLE FOURCHE & CHEYENNE RIVER BASINS
             Reservoir Storage (1000 AF) - End of January               |        Watershed Snowpack Analysis - February 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    115.3     94.0     98.1 |   BELLE FOURCHE               6        51        87
                                                                        |
BELLE FOURCHE                          178.4    175.4    155.8    101.4 |
                                                                        |
DEERFIELD                               15.2     15.4     15.0     12.8 |
                                                                        |
KEYHOLE                                193.8    173.4    148.1     98.7 |
                                                                        |
PACTOLA                                 55.0     52.9     53.6     45.8 |
                                                                        |
SHADEHILL                               81.4     40.5     40.3     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.
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