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

Home Browse Search

5.0 SURFACE WATER 5.1 Streamflow Characteristics A Large Percentage of the Annual Runoff Occurs in Spring and Early Summer Months as Snowmelt from the Higher Elevations In perennial streams in Area 61 the typical seasonal pattern of runoff is base flow from late fall to early spring, a snowmelt peak in spring and early summer months, and occasional to frequent rainfall peaks in the summer months. The typical seasonal pattern of streamflow in Area 61 is shown by a representative hydrograph of mean daily discharge (fig. 5.1 -1). The hydrograph illustrates mean daily flow of the Purgatoire River at Madrid, Colo., during water year 1979. Water year 1979, a year of greater- than - average flow, illustrates the phases of the annual runoff cycle. The flow in the river is virtually base flow from the first of October through the winter months. Beginning in late April to mid -May, snowmelt from the higher elevations of the Culebra Mountains to the west fills the channel with spring runoff. Typically, a large percentage of the annual runoff volume occurs in the spring and early summer months as snowmelt. The sharp peak flows in July, August, and September are from locally intense thunderstorms that occur in the region. As is characteristic of other streams in the area, streamflow in the Purgatoire River is depleted by diversions and is regulated by reservoirs. Upstream from the Madrid gage are about 6,000 acres of irrigated lands and several small onchannel reser- voirs. Average and extreme discharges for the period of record at selected streamflow gages in Area 61 are listed in table 5.1 -1. Average discharge is a some- what misleading statistic for streams in this area because of the large seasonal variation in flow. 38 Predictive equations are available to estimate mean annual flow (Qa), in cubic feet per second for Colorado (Livingston, 1970) and for New Mexico (Borland, 1970). As these equations were developed on a statewide basis it is to be expected that they might be less applicable irr-some areas of the State than in others. The Colorado equation was deve- loped using data predominantly for the mountains of central and northern Colorado. For Area 61, the equations developed for New Mexico, based on comparison of the methods using streamflow - gaging station records from the area, are more applicable. That equation: Qa = 3.24 x 10-5 A1.oi S0.448 pa2.51 LA0.537 has a standard error of estimate of 53 percent. The significant variables are drainage area (A) in square miles, main channel slope (S) in feet per mile, which is the average slope between points 10 and 85 percent of the distance from the site of interest and the drainage divide, the mean October through April precipitation (Pa) in inches (from fig. 5.1 -2), and the latitude at the center of the drainage basin (LA) in degrees minus 30. The above equation is for perenni- al (flowing year around) streams only. No equation exists for streams that are dry for a part of the year.