OPERATING POLICIES FOR A SURFACE/GROUND WATER SYSTEM1

The simulation of the conjunctive use of a surface reservoir and a limestone aquifer is described. The potential yields from each of the sources are of the same order. An important feature of the aquifer is that if the pumpage is reduced, much of the excess water is lost through springs. Five different operating policies are considered which determine whether pumpage should be taken from the reservoir or aquifer. The total safe yields for the historic period 1961–1977 are estimated for each policy and their relative advantages and disadvantages are discussed. The simulation is also carried out for 100 years of generated data to discover the long term consequences.     

SOME SUSPENDED SEDIMENT YIELDS FROM SOUTH ISLAND CATCHMENTS,NEW ZEALAND1

: Estimates of specific annual suspended sediment yields, some of which rank among the highest reported in the world, are presented for 33 basins of South Island, New Zealand. Yield from each basin was determined by combining a suspended sediment concentration rating with the complete flow record of each catchment stream gaging station. A multiple regression analysis between sediment yields and climatic, hydrologic and physiographic parameters of each basin demonstrates that most of the variance in yields is explained by catchment mean rainfall. Geology apparently has little influence on sediment yield as suspended sediment concentration ratings, from rivers draining catchments of differing lithology, and regolith, are indistinguishable. Specific suspended sediment yield prediction equations are given for four defined regions covering in area almost all South Island; and except for one area, feature rainfall as the principle independent variable. Differences between regions may be due to variations in intensity, frequency, and duration patterns of storms. It is proposed that a simple power law relationship between yield and rainfall provides useful suspended sediment yield estimates in mountainous regions of temperate maritime climate, provided catchments have not been modified extensively by man.     

THE POTENTIAL FOR INCREASING STREAMFLOW FROM SIERRA NEVADA WATERSHEDS1

The Sierra Nevada produces over 50 percent of California's water. Improvement of water yields from the Sierra Nevada through watershed management has long been suggested as a means of augmenting the state's water supply. Vegetation and snowpack management can increase runoff from small watersheds by reducing losses due to evapotranspiration, snow interception by canopy, and snow evaporation. Small clearcuts or group selection cuts creating openings less than half a hectare, with the narrow dimension from south to north, appear to be ideal for both increasing and delaying water delivery in the red fir-lodgepole pine and mixed-conifer types of the Sierra west slope. Such openings can have up to 40 percent more snow-water equivalent than does uncut forest. However, the water yield increase drops to 1/2-2 percent of current yield for an entire management unit, due to the small number of openings that can be cut at one time, physical and management constraints, and multiple use/sustained yield guidelines. As a rough forecast, water production from National Forest land in the Sierra Nevada can probably be increased by about 1 percent (0.6 cm) under intensive forest watershed management. Given the state of reservoir storage and water use in California, delaying streamflow is perhaps the greatest contribution watershed management can make to meeting future water demands.     

THE DEVELOPMENT OF A COMBINED WATER QUALITY INDEX1

ABSTRACT: Use-oriented benefits and treatment costs analysis has been incorporated into a water quality index to show an economically optimized concentration for the treatment of the pollutants and the resulting water quality. This combined water quality index can be used in decisionmaking at the federal and local government levels. Five major pollutants, i.e., coliforms, nitrogen, phosphorus, suspended solids, and detergent, have been considered for the municipal waste water. With each higher level of improvement the treatment costs increase accordingly and the benefits associated with the reuse of this treated waste water will increase too but not for the nutrient removal in agricultural use. The optimal concentration is determined when the marginal costs equal the marginal benefits. The combined water quality index is the combination of the maximum net benefits and the water quality index of the optimized residual concentrations. This water quality index is zero dollars for the Tucson region in this study. The possible reclaimed use of municipal waste water is for agricultural irrigation and recreational lakes for the Tucson region.     

LOCATION OF MUNICIPAL WELL FIELDS IN AN ENVIRONMENTALLY SENSITIVE REGION1

ABSTRACT: A visual selection technique can be utilized to locate potential well field sites prior to on-site testing. The technique is based upon an understanding of the regional hydrology and an appreciation for development goals such as the identification of high-yield and low-impact locations. Although the uniqueness of Pasco, Pinellas, and Hillsborough Counties in Western Florida has been incorporated into the current application, the methodology, with modifications, is transferable to other geographic regions. Overlays of each criterion used in site selection are combined to form a regional composite showing favorable site locations and further serve a useful communications role as visual aids during public presentation. Implications of direct and indirect cost savings to the public are obtained when the methodology is applied to the location of municipal well fields.     

DECISION SUPPORT SYSTEM FOR MANAGING GROUND WATER RESOURCES IN THE CHOUSHUI RIVER ALLUVIAL IN TAIWAN1

ABSTRACT: Ground water is a vital water resource in the Choushui River alluvial fan in Taiwan. A significantly increased demand for water, resulting from rapid economic development, has led to large scale ground water extraction. Overdraft of ground water has considerably lowered the ground water level, and caused seawater intrusion, land subsidence, and other environmental damage. Sound ground water management thus is essential. This study presents a decision support system (DSS) for managing ground water resources in the Choushui River alluvial fan. This DSS integrates geographic information, ground water simulation, and expert systems. The geographic information system effectively analyzes and displays the spatially varied data and interfaces with the ground water simulation system to compute the dynamic behavior of ground water flow and solute transport in the aquifer. Meanwhile, a ground water model, MODFLOW‐96, is used to determine the permissible yield in the Choushui River alluvial fan. Additionally, an expert system of DSS employs the determined aquifer permissible yield to assist local government agencies in issuing water rights permits and managing ground water resources in the Choushui River alluvial fan.     

DECISION FRAMEWORK FOR SEDIMENT CONTROL IN MUDDY CREEK WATERSHED1

ABSTRACT: The tailwater of Bridgewater Dam, below Lake James, North Carolina, is a designated trout stream. It has environmental attributes for a good cold water fishery with the exception of high suspended sediments. Muddy Creek, a tributary about 1.5 km downstream of the dam, is a major source of sediments. The Muddy Creek Watershed Restoration Initiative was established to develop and implement a sediment control plan. The Watershed Analysis Risk Management Framework was applied to simulate soil erosion and sedimentation and to help determine appropriate action. The simulated sediment concentrations of the river were comparable to observed data from November 1994 to November 2001. For the base condition, the sediment load was 135,000 kg/d from surface erosion and 1,300,000 kg/d from bank erosion. Increasing the buffer strip from existing 50 to 80 percent to 100 percent of stream segments would only reduce surface erosion to 70,400 kg/d with little change in sediment concentrations. Eliminating riverbank erosion would reduce the sediment load from 920,000 to 87,700 kg/d. The bank stabilization project would not only lower suspended sediment concentrations for Muddy Creek, but also reduce the lake sediment accumulation in the downstream Lake Rhodhiss by approximately 13 percent.     

AN ANALYTICAL FRAMEWORK FOR EVALUATING CHANNEL MAINTENANCE FLOWS IN COLORADO1

ABSTRACT: An accounting procedure is developed which determines a flow regime that is capable of transporting an amount of bedload sediment necessary to ensure channel stability downstream. The method allows for sediment buildup in the channel within geomorphic threshold limits during low flow periods. During periods of high runoff, enough water is bypassed to transport the stored sediment. The procedure utilizes only those flows of sufficient magnitude to maintain channel stability over the long run (25–50+ years). An example is presented which determines the volume of water and frequency of release for channel maintenance purposes downstream from a hypothetical water diversion project. Of some 1,200,000 acre feet generated during a 59-year period, 86,500 acre feet was required for channel maintenance flows. Bypass flows were not required each year, but only during those years when average daily flow reached bankfull or greater. Such releases were made on 202 of the 411 days when average flows either equalled or exceeded bankfull discharge.