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tv o 0) N The study section is underlain by undivided Mancos Shale (Ponce 1975). After the stream leaves the Book Cliffs, it mean- ders through a valley between steep clefted pediments on the east and west.. The valley is approximately 3 miles wide and consists of rolling hills and pediment remnants. The terrain is dissected by numerous ephemeral streams that have cut deep and narrow channels through the easily eroded Mancos Shale. The vegetation is predominantly mixed sagebrush and grasses. A small farm of approximately 180 acres (1.29 percent of the drainage area) is located along the base of the Book Cliffs. During much of the summer, the entire flow of the creek is diverted to irrigate alfalfa at a location immediately downstream from the upper control site (Figure 3.1). Our ing diversion periods '(except during runoff events), the channel is essentially dry for approximately 1.5 miles downstream. At this point, small quantities of flow (possibly return flows from the i rr iga ted area) beg i n to accumulate in the channel. Further downstream, flows are augmented by tributary inflow. Conductivity measurements during the summer of 1975 indicated a general increase in the salinity of the Coal Creek waters as the stream moved southward across the Mancos Shale. ~ ~ i i Coal Creek was instrumented at the upstream and downstream control points (Figure 3.1) with the following equipment: 1. Recording Kernco model CR-15 conduc- tivity meters. 2. Rustrack dual channel temperature recorders, model 2133, 3. Electronic staff gage recorders (constructed by Duard Woffinden, UWRL). A third site was chosen near the middle of the study section and a staff gage in- stalled. The following instruments were installed: 1, Belfort S/349A anemometer. 2. Casella thermo-hydrograph, #931. 3. Belfort recording raingage. 4. Micromet net radiometer, #R421 (damaged shortly after installation). Four raingages (Figure 3.2) also were in- stalled within the experimental drainage. Installation of the above equipment was completed on July I, 1976. Stream SamplinR and Field Tests Some samples were taken as early as May 1976, and regular weekly water quality sampling was begun in JUne. Sampling con- tinued until December 1976. Channel soil samples were taken from 20 -different sites (Figure 3.2). At each site, samples were taken at three depths from the channel bed and bank materials: 0-4 inches, 4-8 inches, and 8-12 inches. One-to-one saturation extracts were run on the samples by the Soils Laboratory at Utah State Un1versity. (Appendix A describes the methods used.) The data taken are recorded in Appendix C. Field permeability tests were run in the main channel of Coal Creek. Four-inch diameter test holes were augered at a distance of 3 feet from the stream edge to a depth of approximately 3 feet. The channel bed was assumed to be saturated, and perme- ability was estimated from the recharge rate at the test hole (Bureau of Reclamation, undated). Test holes were dug at sites I, 3, 5, and 9 (Figure 3.2). A cable was strung across the lower site to aid in measuring streamflow during storm events. Apparatus and equipment for flow measurement and quality samplings, including sediment load, were stored on site. Because of the possible danger from flood flows, no field observations were made during major storm events. To study salt pickup mechanisms under conditions of controlled channel flow, a small, natural ephemeral channel was selected which could be supplied with water at specif- ic flow rates from an irrigation ditch. The channel is contained entirely in Mancos Shale and slopes southward at approximately 2.5 percent. Water was released from a small flume which conveys irrigation water over the natural channel. HS flumes (USDA 1962). equipped with Leopold and Stevens model 61, 12-hour recorders, were installed in the channel at four locations (Figure 3.3). Water conductivity measurements were made in the field. Sediment samples were obtained from the bottom of the flumes and filtered through GS/A 12,s-cm glass fiber filters. One-half of the samples were placed in 500 ml of distilled water and the conductivity monitored. The remaining sediment was left to air dry for later laboratory analysis. Flow was induced on two separate occasions, August 26 and September 9, 1976. On August 26, water quality samples were obtained in addition to flow and con- ductivity measurements. On September 9, only flow and conductivity measurements were made. During both tests, water was diverted down the channel until little salt pickup remained. Prior to the above induced flows, 12 soil salinity sensors made by Soil Moisture Equipment Corporation (Model #sOOOA) were placed in the channel. Three sites were monitored (Figure 3.3) with sensors placed in the following manner: 19