Belle Fourche and Cheyenne River Basins (7)
April 2001

Snow
Snow Water Equivalent (SWE) in the Belle Fourche River basin, as of April 1, is 126 percent of normal. This is 265 percent of what it was last year at this time. See Basin summary of Snow Course Data at the beginning of this report for a detailed listing.

Precipitation
Precipitation, for the month of March was 79 percent of average in the Black Hills (125 percent of last March). Monthly percentages range from 26 to 156 percent. Year-to-date precipitation is 99 percent of average and 154 percent of last year's amount. Year to date percentages range from 81 to 146. This is from the 3 reporting stations.

Reservoir
Usable reservoir storage is generally above average in the basin. Angostura is currently storing 99 percent of average (108,600-acre feet). Belle Fourche reservoir is storing 135 percent of average (176,500-acre feet). Deerfield reservoir is storing 112 percent of average (15,100-acre feet). Keyhole reservoir is storing 156 percent of average (167,700-acre feet). Pactola reservoir is storing 116 percent of average (54,300-acre feet), and Shadehill reservoir is storing 131 percent of average (82,700-acre feet).

Streamflow
Streamflow forecasts are below average as of April 1. Deerfield Reservoir inflow is forecast at 2,500 acre feet (60 percent of average). Pactola is forecast at 10,000 acre feet (53 percent of average). This is for the April - July runoff period. 

 
==================================================================================================================================
                                              BELLE FOURCHE & CHEYENNE RIVER BASINS
                                               Streamflow Forecasts - April 1, 2001
==================================================================================================================================
                                              |  <<====== 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           APR-JUL      0.88      1.85    |     2.50        60    |      3.59      5.20           4.20
                                                                    |                       |
PACTOLA RESERVOIR Inflow             APR-JUL       0.8       6.3    |     10.0        53    |      17.0        27           18.9
                                                                    |                       |
==================================================================================================================================
                  BELLE FOURCHE & CHEYENNE RIVER BASINS                 |          BELLE FOURCHE & CHEYENNE RIVER BASINS
             Reservoir Storage (1000 AF) - End of March                 |        Watershed Snowpack Analysis - April 1, 2001
==================================================================================================================================
                                      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    108.6    120.5    110.1 |   BELLE FOURCHE               6       278       126
                                                                        |
BELLE FOURCHE                          178.4    176.5    180.2    130.9 |
                                                                        |
DEERFIELD                               15.2     15.1     15.0     13.5 |
                                                                        |
KEYHOLE                                193.8    167.7    174.7    107.6 |
                                                                        |
PACTOLA                                 55.0     54.3     54.1     46.8 |
                                                                        |
SHADEHILL                               81.4     82.7     56.3     63.1 |
                                                                        |
==================================================================================================================================
 * 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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