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N o ~ OJ 4. Integrate the selected relationships into a mathematical model of the natural processes loading the stream with salts. 5. Employ the hydrosalinity model in analysis of the contribution of salt loadings from natural areas in the Price River Basin. f Significance of the Study A well founded understanding of salt loading processes is required to develop effective salinity management programs for the arid Colorado River Basin. The under- standing needs to identify and describe the physical processes picking salt up from diffuse sources and carrying it downstream, establish quantitative relationships for estimating salt loading and transport, and thereby provide a basis for selecting promising land and water management p~ograms and predicting how well they will perform. The effort to build that understanding has been severely handicapped by the paucity of data on salt movement. Hence, this study seeks both to collect data and to model, to do both 'simultaneously in an interactive way with the hope of advancing more quickly to the needed understanding. According to Hyatt et a1. (1970), "Research is needed to improve relationships for predicting water quality as a function of parameters such as various watershed chsracterist ics and hydrology. Because of the complex processes which occur in a watershed, it is likely these relationships will need to be empirical in nature. As improved relationships are developed, the(. can be incorporated into system models. ' This project developed a first generation mathematical model capable of simulating the major salinity uptake mechanisms from an ephemeral catchment in the Mancos Shale wildlands. Such simulation begins quantita- tive definition of relationships between catchment characteristics and salt loading in a rigorous way that can later be used in examining ways a salinity control program can reduce salt loading. Without the discipline of a verified model for their assessment, management proposals are only guesses. ~ t Literature Review Streamflow and salinity functions In one of the first formal studies of salt movement in semiarid western streams, Hem (1948) found that total dissolved solids (TDS) varied with flow in an inverse manner. Seasonal and diurnal variations were both found. A typical salt concentration versus stream flow relationship is shown in Figure 1.2 for the Gila River at Bylas, Arizona, for six storm events. Hem (1948) hypothesized that rising conductivity curves are due to dissolution of salts left in the channel by precipitation and evaporation; and that falling conductivity curves are the result of dilution. -..; 600 0 ~ N ~ flj 500 ~ :::: " ~400 . g ~300 " " -g 8200 " ''; '" '8100 . '" 00 00 2000 0 '" -:; . 1000 '" >< . .c " . 0 ''; '" Gila River at Bylas. Arizona 10 15 20 August 1943 25 31 5 Figure 1.2, Daily conductance and the mean daily discharge measurements for the Gila River at Bylas> Arizona, during August 1943 (taken from Hem 1948), Durum (1953) studied the salt-discharge relationships for the Saline River, Kansas. He observed the average chloride concentra- t ion to be directly proportional to the IDS and proposed the following relationship for relating mean chloride concentration to mean flow: Cc k/Q.........,.. (1.1) in which Cc Chloride concentration in mgfl Q Water flow rate in cfs k Constant In testing his equation with empirical data, Durum (1953) had a correlation coeffi- cient of 0.94. The chloride concentration was found to be high and highly variable at low water flow rates and low at high flows (Figure 1.3). During periods of rapidly rising stages, however, the chloride concen- tration was observed to increase. The author attributed this anomaly to the dissolution of soluable materials deposited in the channel bed as water evaporates during low flows and then scoured out and carried as suspended or bed load with the rising flow. He estimated the contribution of salt from groundwater by assuming that flow during the winter months equals the groundwater inflow. 3