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5.0 SURFACE WATER--Continued 5.3 Duraflon of Flow Time Distribution of Streamflow is Illustrated by the Flow-lluration 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 6I. The five Stream- flow-gaging stations are shown in (figure 5.3-I, 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 (or the period prior to 1976 when construction otTrinidad Dam was completed. A (low-duration curve with a consistent steep slope indicates variable Streamflow resulting from direct surface runoff or upstream diversions (Living- ston and others, 1976). Doth conditions exist for the Canadian River near Hebron at station 23. A flow- duration curve having a (latter slope, especially at the lower end, indicates streamllow from delayed surface runoff and ground-water storage. Strcamflow- gaging stations 5, 18, 30, and 40 (fig. 5.3-I) are in this category. (Note that stations IB, 30, and 40 have steeper slopes at the lower end than station 5, as shown in fig. 5.3-2.) Station S is affected by fewer upstream d(versions than the other three stations and is nearer to the headwaters. Mountain areas above 10,000 feet contribute delayed runoff from snowmel[ during a normal season (fig. 5.3-1). Stations 18, 30, and 40, which are affected by snowmel[ 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 (or irrigation during the growing season.