Hydrology of Cornfield Wash area and effects of land-treatment practices, Sandoval County, New Mexico, 1951-60

Abstract

The collection of runoff and sediment data was the primary objective of the 10-year (1951-60) study in the Cornfield Wash basin, which has an area of 21.3 square miles. However, reconnaissance investigations also were made of (1) precipitation; (2) the effects of reservoirs on runoff, erosion, and sediment yield; (3) the effects of range pitting on runoff, sediment, and vegetation yields; and (4) the effects of wire sediment barriers on sediment accumulations. Precipitation averaged 6.07 inches for the warm season (May 1 through October 31). From 1951 to 1955 much of the precipitation came in short torrential downpours. Since 1955, precipitation usually has been of lower intensity, resulting in a low runoff-precipitation ratio. The total composite inflow to the 19 reservoirs in the Cornfield Wash basin--12 constructed in 1950 and 7 constructed from 1953 to 1956--was 5,720 acre-feet. The reservoirs permanently retained 1,370 acre-feet of water, 43 percent of which was apparently lost by evaporation. The average seasonal runoff (1951-59) from the ephemeral streams of the Cornfield Wash basin and nearby watersheds can be expressed, with a high coefficient of correlation, by the equation: runoff = 29.4 (area) 0.82 acre-feet. This relation suggests that there is a good correlation between the size of the drainage basin and the basin characteristics that most influence travel time of runoff. Comparisons of readily measurable basin characteristics that influence travel time indicate: 1. Land slope is proportional to (area) .0.035; 2. Length of longest watercourse is proportional to (area) 0.52; 3. Distance along the longest watercourse from gaging station to a point opposite the center of drainage basin is proportional to (area)0.52; and 4. Equivalent channel slope is proportional to (area)- 0.027. Except for land slope, the coefficients of correlation for each of the basin characteristics-area relations were relatively high. The correlation between seasonal runoff (1951-60) from the small watersheds of the Cornfield Wash basin and the size of the drainage basin was improved after correcting for the influence of land slope. The original total storage capacity of the 19 reservoirs was reduced from 845 to 455 acre-feet as a result of the impoundment of 390 acre-feet of sediment. Backwater from the reservoirs influenced the deposition of an additional 20 acre-feet of sediment. The average annual accretion of sediment (1951-60) in the reservoirs of the Cornfield Wash basin can be expressed by the equation: sediment - 0.0119 (seasonal runoff) 1.3 (incised channel density) 0.71. By removing seasonal runoff as a variable, the average annual sediment accretion is proportional to (area) 1.19 (incised channel density) 1.3. Conservation and rehabilitation of damaged land were successful in some instances and only partly successful in others. The reservoirs are effective in inducing sediment accretion upstream; also, they stop the advance of abrupt headcuts below the reservoirs, but only as long as the spillage is not great and the spillway stays intact. In addition, the reservoirs are effective in reducing flood peaks. A longer period of study is necessary to define adequately the effectiveness of the wire sediment barriers. The data collected on range-pitting effects were not complete enough to. define the magnitude of the changes, if any, in runoff, sediment, and vegetation yields.