Belle Fourche and Cheyenne River Basins (7)
June 1999

Snow
As of June 1, the Belle Fourche River basin is melted out. It was also melted out at this time 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 May was 99 percent of average in the Black Hills (141 percent of last May). Monthly percentages range from 60 to 124 percent. Year-to-date precipitation is 126 percent of average and 138 percent of last year's amount. Year to date percentages range from 104 to 158. This is from the 4 reporting stations.

Reservoir
Reservoir storage is above average in the basin. Angostura is currently storing 103 percent of average (121,100-acre feet). Belle Fourche reservoir is storing 123 percent of average (186,800-acre feet). Deerfield reservoir is storing 112 percent of average (15,200- acre feet). Keyhole reservoir is storing 158 percent of average (179,900-acre feet). Pactola reservoir is storing 113 percent of average (54,900-acre feet), and Shadehill reservoir is storing 114 percent of average (78,300-acre feet).

Streamflow
Black Hills water users should see average runoff during the June through July forecast period. The 50 percent chance runoff for Castle Creek below Deerfield Dam is estimated to be 97 percent of average (1,750 acre feet). The 50 percent chance runoff for Rapid Creek below Pactola Dam should be about 9,150 acre feet (102 percent of average). 

==================================================================================================================================
                                              BELLE FOURCHE & CHEYENNE RIVER BASINS
                                               Streamflow Forecasts - June 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           JUN-JUL      0.39      1.20    |     1.75        97    |      2.30      3.11           1.80
                                                                    |                       |
PACTOLA Reservoir Inflow             JUN-JUL      0.48      5.64    |     9.15       102    |     12.66     17.82           9.00
                                                                    |                       |
==================================================================================================================================
                  BELLE FOURCHE & CHEYENNE RIVER BASINS                 |          BELLE FOURCHE & CHEYENNE RIVER BASINS
             Reservoir Storage (1000 AF) - End of May                   |        Watershed Snowpack Analysis - June 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    121.1    119.6    117.2 |   BELLE FOURCHE               2         0         0
                                                                        |
BELLE FOURCHE                          178.4    186.8    171.8    152.3 |
                                                                        |
DEERFIELD                               15.2     15.2     15.2     13.6 |
                                                                        |
KEYHOLE                                193.8    179.9    178.8    113.6 |
                                                                        |
PACTOLA                                 55.0     54.9     54.9     48.6 |
                                                                        |
SHADEHILL                               81.4     78.3     71.0     68.7 |
                                                                        |
==================================================================================================================================
 * 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.
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