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about May 24 to June 20. The flood of 1927 was the highest since stream gage records have been kept. This flood was caused by melting snow and increased by precipitation. I I I I I I- I I I I I I I I I I Recent high flows occurred during 1979, 1985, 1986, and 1987 in the Alamosa area, only a successful flood fighting effort by local government in all four years prevented substantial damage within the Alamosa area. Also, the channel clearance and willow mowing in October of 1985 contributed significantly to the no damage effect during 1986 and 1987 peak flows. In addition, irrigation diversions and operation plan for the Rio Grande Reservoir can play an important role in determining flood stage to downs tream communities. The Rio Grande Reservoir can store up to 52,500 acre feet and the irrigation canal systems can divert up to 4,000 cfs. The Albuquerque District, hydrology for the Rio Grande gage data for their analysis. Corps of Engineers developed at Alamosa using recorded stream The hydrologic data for the flood impacted reach of the Rio Grande is presented in Table 2. Table 2. Rio Grande Flood Discharges Drainage Flood Frequencv Location Area 10-vear 50-vear 100-vear 500-vear Alamosa 1710 4,600 9,000 10,900 18,000 Monte Vista 1590 9,320 11. 850 12,880 15,150 Del Norte 1320 7,701 9,879 10,734 12,608 South Fork 1164 7,360 10,620 12,230 16,530 3.1 The Flood of June 1985 3.1.1 Magnitude Hot temperatures and an unusually heavy late snowpack upper reaches of the Rio Grande basin combined to unusually rapid runoff from June 8 through June 14, 1985. in the cause The following peak discharge was recorded on the stream gages at Alamosa (Table 3). Table 3. Recorded Peak Discharges Location Date Time Discharqe Peak Alamosa Alamosa Wed., June 11, 1985 Sat., May 16, 1987 Midnight 4,420 cfs 5,160 cfs In comparing the recorded peak discharges with the flood frequency information, it appears that the magnitude of the 1985 flood ranged from about one in a 30-year event above Del Norte to about a one in 10-year event in Alamosa. -3-