Hydrology of Area 61, Northern Great Plains and Rocky Mountain Coal Provinces, Colorado and New Mexico

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5.0 SURFACE WATER -- Continued 5.3 Duration of Flow Time Distribution of Streamflow Is Illustrated by the Flow - Duration Curve Flows in streams draining foothill areas are poorly sustained in comparison with those draining the mountain environment. The time distribution of streamflow is illustrated by the flow- duration curve. Five streamflow- gaging stations were selected to illustrate the diversity of flow characteristics within Area 61. The five stream- flow- gaging stations are shown in figure 5.3 -1, and their respective flow- duration curves are shown in figure 5.3 -2. Flow- duration curves show the percent- age of time that a specific discharge was equaled or exceeded during a given time. All flow - duration curves shown in figure 5.3 -2 represent the period of record for each station with one exception. The flow- duration curve for streamflow- gaging station 18 (fig. 5.3 -1) is for the period prior to 1976 when construction of Trinidad Dam was completed. A flow - duration curve with a consistent steep slope indicates variable streamflow resulting from direct surface runoff or upstream diversions (Living- ston and others, 1976). Both conditions exist for the Canadian River near Hebron at station 23. A flow - duration curve having a flatter slope, especially at the lower end, indicates streamflow from delayed surface runoff and ground -water storage. Streamflow- 42 gaging stations 5, 18, 30, and 40 (fig. 5.3 -1) are in this category. (Note that stations 18, 30, and 40 have steeper slopes at the lower end than station 5, as shown in fig. 5.3 -2.) Station 5 is affected by fewer upstream diversions than the other three stations and is nearer to the headwaters. Mountain areas above 10,000 feet contribute delayed runoff from snowmelt during a normal season (fig. 5.3 -1). Stations 18, 30, and 40, which are affected by_snowmelt and are sustained by water from the Raton Formation during low -flow periods, have similar duration curves (fig. 5.3 -2). At station 5, the flow is sustained because the station is located in the headwater area of the Cu- charas River where precipitation is greatest. Station 20 on the Canadian River is poorly sustained because the basin is at a lower altitude and receives less precipitation in the form of snow; also, water is diverted for irrigation during the growing season.