From this review it becomes apparent that several causal relationships may exist 

 between contour trenching and water yield. A more thorough understanding of trenching 

 effects is necessary to adequately determine what changes, if any, in water yield or 

 water quality occur when a watershed is trenched. The results reported here are the 

 outcome of research conducted on two Utah watersheds. Halfway Creek and Miller Creek. 

 Contour trenching is evaluated in terms of: 



(1) Total annual streamflow; 



(2) Characteristics of spring streamflow (total and peak volumes and 

 recession); and 



(3) Low streamflow (July through February) with respect to total 

 volume of streamflow from these watersheds. 



DESCRIPTION OF AREA 



The contour trenches used in this study are in Halfway Creek drainage, a tributary 

 of the 10-square-mile Farmington Canyon watershed northeast of Farmington, Utah 

 (fig. 1). Within Farmington Canyon are a couple of snow courses, a network of precipi- 

 tation gages, and small watersheds which have streamflow records of varying lengths. 

 Of these. Miller Creek drainage was selected as the control. The Halfway Creek drain- 

 age produced floods from summer storms in 1926, 1936," and 1947 because of the badly 

 denuded condition of portions of its headwaters area. This drainage and those adjacent 

 to it have been closed to livestock grazing since the late 1930 's. 



Topography, Geology, and Soils 



On this west face of the Wasatch range, the transition is abrupt from the Great 

 Basin valley floor (elevation 4,200 feet) to the peaks of the Wasatch Mountains. 

 Within the 464-acre Halfway Creek drainage, elevation ranges from 6,200 feet at the 

 mouth to 9,000 feet near Francis Peak (9,547 feet). Elevation within the Miller Creek 

 drainage ranges from 6,500 feet to 8,500 feet. The steep stream gradients (approxi- 

 mately 38 percent) for the two drainages are illustrated in figure 2. Halfway Creek's 

 main channel is slightly over 1 mile long. Miller Creek's is approximately two-thirds 

 of a mile long. 



A comparison of the Halfway Creek and Miller Creek drainages is given by the dimen- 

 sionless area-elevation curve (Aronovici 1966) in figure 3. Had the two drainages 

 been similar in configuration, the two curves would have coincided along their entire 

 length. The departure of the curves reflects the greater percentage of Miller Creek 

 drainage at the higher elevations. 



Halfway Creek faces southwest and Miller Creek north, and their contrasting aspects 

 contribute to differences in precipitation patterns and vegetation. However, as 

 extremely different as the two watersheds appear to be, their hydrographs react quite 

 similarly as will be shown later in the analysis. 



The Halfway Creek drainage has a fine network of tributaries. Many of these are 

 headed by perennial springs that originate along the broad contact zone just below the 

 trenched area. Numerous intermittent stream channels extending into the trenched area 

 are deeply incised. Major channels in the Halfway Creek drainage are V-shaped (10 to 

 20 feet deep, 40 to 60 feet in width) and usually eroded down to bedrock. Stream 

 channels in Miller Creek do not reflect this degree of cutting, being less than 10 feet 

 deep and 20 feet wide. 



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