Operation of the Garrison Diversion Unit in North Dakota may have various effects on the quantity and quality of streamflow in the Sheyenne River and the Red River of the North. To model the effects that the Garrison Diverson Unit could have on water quantity, monthly gaged and estimated streamflow data and estimated unregulated streamflow data were compiled to develop a complete monthly streamflow record for January 1931 through December 1984 (data-development period) for 29 sites in the Red River of the North basin.
Gaged streamflow records were available for January 1931 through December 1984 for only 4 sites; no records or records of various length were available for the remaining 25 sites. Drainage-area ratio and Maintenance of Variance Extension Type 1 methods were used to estimate the streamflow for those sites that had no streamflow record or had a streamflow record available for only part of the data-development period.
Unregulated streamflow for the 29 sites was estimated by removing the hydrologic effects of Lake Ashtabula, which is formed behind Baldhill Dam on the Sheyenne River, and surface-water withdrawals. VIater-balance procedures were used to remove the hydrologic effects of Lake Ashtabula from the streamflow record for sites downstream of Baldhill Dam.
Mean annual gaged streamflow for the Sheyenne River below Baldhill Dam was 9,175 acre-feet less than mean annual estimated unregulated streamflow for 1950-84, when Baldhill Dam was in operation. Net evaporation losses from Lake Ashtabula account for most of the difference between gaged streamflow and estimated unregulated streamflow.
