Laserfiche WebLink
<br /> <br />002636 <br /> <br />figure 8, and the respective values were plotted against the <br />computed sediment yields. For this comparison, shown in figure <br />ment yields .were adjusted to 1,500 mi2 (3,90D km2), in order to <br />with the Langbein-Schumm (1958) relation. <br /> <br />corresponding <br />10, all sed 1- <br />be compa t i b 1 e <br /> <br />The sediment yields determined at 13 of the 17 gaging stations are <br />considerably less than the estimates that would have been made using the <br />Langbein-Schumm (1958) relation, as shown in figure 10. This discrepancy may <br />be explained, In part, by recent regional trends towards channel aggradation. <br />Studies by Leopold, Emmett, and Myrick (1966) and Emmett (1974) have shown <br />that small perennial and ephemeral stream channels throughout the Rocky <br />Mountain region have been aggrading since about 1950; that is, sediment is <br />being stored In the channel network. L. M. Brush (oral commun., 1977) noted <br />extensive and rapid aggradation of some stream channels tributary to the <br />Little Snake River during the late 195D's and early 1960's. In contrast, <br />channel degradation was widespread throughout the region from 1880 to 1950 <br />(Bailey, 1935; Bryan, 1941; Hack, 1942; Thornwaite and others, 1942; Leopold. <br />and Miller, 1954; Miller and Wendorf, 1958). The factors that have caused <br />this regional change are not well understood. Unfortunately, no sediment <br />records at gaging stations in the Yampa River basin cover the pre- and post- <br />1950 period sufficiently well to confirm that sediment loads have actually <br />decreased. Only four dally sediment stations were operated in the Colorado <br />River basin prior to 1948, and all of these have been affected by the <br />construction of large reservoirs In the past 30 years. <br /> <br />The data used by Langbein and Schumm (1958) In their nationwide study <br />were collected prior to 1957 and therefore represent primarily a pe~iod prior <br />to observed channel aggradation. Conversely, most of the data used in this <br />investigation for the Yampa River basin have been collected since 1975, and <br />no data were collected prior to 1950. Thus, the data for the Yampa River <br />basin represent the period of observed channel aggradation. Therefore, it is <br />probable that generally smaller sediment yields have occurred for a given <br />amount of mean-annual precipitation, as indicated in figure 10. This <br />decrease in sediment yield probably Is due to the storage of sediment In the <br />channels of small streams throughout the Yampa River basin. <br /> <br />ESTIMATED INCREASE IN SEDIMENT YIELDS DUE TO SURFACE <br />MINING IN THE YAMPA RIVER BASIN <br /> <br />Large Increases in the volume of coal mined from the Yampa River basin <br />are anticipated during the next 15 years. Most of the additional production <br />during the next 15 years will be by surface mining (U.S. Department of the <br />Interior, 1976; Udis and others, 1977). As a result, there will be an <br />increase in land disturbance and probably an increase In the quantity of <br />sediment supplied to the stream channels draining the surface-mined areas. <br />The Surface Mining Control and Reclamation Act of 1977 (Pub I ic Law 95-87) <br />requires that surface-mined areas must be reclaimed and revegetated according <br />to specified standards. During and Immediately following mining, however, <br />the hlllslopes will be ,unvegetated, will have no soil, and,in many instances, <br /> <br />25 <br /> <br />,'~' <br />