Management of a large river basin requires information regarding the interactions of variables describing the system. A method has been developed to determine these interactions so that the resources management within a given river basin can proceed in an optimal way. The method can be used as a planning tool to display how different management alternatives affect the behavior of the river system. Direct application is made to the Colorado River Basin.
The Colorado River has a relatively low and highly variable streamflow. Allocated rights to the consumptive use of the river water exceed the present long-term average flow. The naturally high total dissolved solids concentration of the river water continues to increase due to the activities of man. Current management policies in the basin have been the products of compromises between the seven states and two countries which are traversed by the river or its tributaries. The anticipated use of the scarce supply of water in the extraction and processing of energy resources in the basin underwrites the need for planning tools which can illuminate many possible management alternatives and their effects upon water supply, water quality, power production, and the other concerns of the Colorado River water users.
A computer simulation model has been developed and used to simulate the effects of various management alternatives upon water conservation, water quality, and power production. The model generates synthetic sequences of streamflows and total dissolved solids (TDS) concentrations. The flows of water and TDS are then routed through the major reservoirs of the system, Lakes Powell and Mead.
Characteristics of system behavior are examined from simulations using different streamflow sequences, upstream depletion levels, and reservoir operating policies. Reservoir evaporation, discharge, discharge salinity, and power generating capacity are examined.
Simulation outputs show that the probability with which Lake Powell fails to supply a specified target discharge is highly variable. Simulations employing different streamflow sequences result in probabilities of reservoir failure which differ by as much as 0.1.
Three levels of Upper Colorado River Basin demands are imposed on the model: 3.8 MAF/yr (4.7 km^3/yr), 4.6 MAF/yr (5.7 km^3/yr), and 5.5 MAF/yr (6.8 km^3/yr). Two levels of water demand are imposed below Lake Mead: 8.25 MAF/yr (10.2 km^3/yr) and 7.0 MAF/yr (6.8 km^3/yr).
Although the effects of reservoir operations upon water quality are made uncertain by a lack of knowledge regarding the chemical limnology of Lake Powell, two possible lake chemistry models have been developed, and the predicted impacts of changes in reservoir operation upon water quality are presented.
The current criteria for the operations of Lakes Powell and Mead are based upon 75 years of compromises and agreements between the various water interests in the Colorado River Basin. Simulations show that Lake Powell will be unable to conform to these operating constraints at the higher levels of water demand.
An alternative form of reservoir operation is defined and compared to the existing policy on the basis of reliability of water supply, conservation of water, impact upon water quality, and the effect upon power generation.
Ignoring the current institutional operating constraints, and attempting only to provide a reliable supply of water at the locations of water demand, is shown to be a superior management policy. This alternate policy results in the conservation of as much as 0.25 MAF/yr (0.3 km^3/yr) of water. The impact of the alternate operating policy upon hydroelectric power generation and the potential use of the conserved water for development of energy resources is discussed
