SENSITIVITY OF GROUNDWATER FLOW MODELS TO VERTICAL VARIABILITY OF AQUIFER CONSTANTS1

ABSTRACT: The Ogallala aquifer in the Oklahoma Panhandle is in need of better management because of increased groundwater demand which has caused declines in static water levels at an alarming rate. A groundwater management computer model was developed for the Ogallala aquifer in the Texas Panhandle and treats the aquifer as a homogeneous system. In this study, the computer model has been modified in order to evaluate the effects of vertical layering on semi-static water level changes which occur during the dewatering of a single unconfined aquifer. The modified model was applied to a study area near Guymon, Oklahoma, using both the homogeneous and the multilayered cases. The aquifer is characterized by a saturated thickness of 400 feet. The accumulated drawdown values of the homogeneous and the multilayered cases demonstrate that an average difference of approximately 22% of the original saturated thickness occurs between the two cases before the base of the aquifer is encountered. Approximately 25% more time is required to dewater the layered aquifer. Thus, vertical variations of lithology in an aquifer such as the Ogallala should be considered when prediction is made relative to groundwater management.     

CHEMISTRY OF MUD-WATER INTERFACE IN AN IMPOUNDMENT1

ABSTRACT: Lake Evergreen was investigated during the time of filling and thereafter for the change of water chemistry at the mud-water interface. The results show that aging or maturing occurs at the nascent stage of the impoundment history. There are many factors affecting concentration of chemical constituents at the interface. There are hydrologic changes such as wind and wave action, or water circulation which can influence all chemical parameters. There is also biological activity, which may involve changes in concentrations of silica, phosphate, alkalinity, pH, ammonium, Kjeldahl nitrogen, etc. An associated effect is the reduction of oxidation-reduction potential which in turn affects the concentration of manganese, etc. All these changes occur primarily in autumn. In late spring to summer, there are changes of nitrite and nitrate accompanied by changes in dissolved oxygen. A water chemistry model at the interface is illustrated.     

LONG-TERM VARIATIONS IN SEASONAL WEATHER CONDITIONS IMPORTANT TO WATER RESOURCES IN ILLINOIS1

ABSTRACT: An analysis of historical relationships between seasonal weather conditions and water resource conditions in Illinois provides insights to the challenges of projecting such relationships under conditions of climate change. In Illinois for 1901–1997 there were major temporal shifts in types of seasonal conditions that have positive and negative effects on surface water and ground water supplies and their quality. Major seasonal effects came in the spring and summer seasons and when either wet-and-warm or dry-and-warm weather conditions prevailed in either season. Sixty percent of the summer seasons creating negative impacts occurred during only 40 years: 1911–1940 and 1951–1960. Seasons creating impacts relate well to the frequency of cyclone passages and to the incidence of El Niño or La Niña conditions. This reveals that future climate fluctuations that shift the frequency of cyclones and/or ENSO events will have profound effects on Midwestern seasonal conditions that affect water resources. Projecting future effects of climate change on water resources will need to consider how shifts in water use and water management technologies act to re-define the seasonal weather conditions that are critical.     

SENSITIVITY OF HIGH-ELEVATION STREAMS IN THE SOUTHERN BLUE RIDGE PROVINCE TO ACIDIC DEPOSITION1

ABSTRACT: The Southern Blue Ridge Province, which encompasses parts of northern Georgia, eastern Tennessee, and western North Carolina, has been predicted to be sensitive to impacts from acidic deposition, owing to the chemical composition of the bedrock geology and soils. This study confirms the predicted potential sensitivity, quantifies the level of total alkalinity and describes the chemical characteristics of 30 headwater streams of this area. Water chemistry was measured five times between April 1983 and June 1984 at first and third order reaches of each stream during baseflow conditions. Sensitivity based on total alkalinity and the Calcite Saturation Index indicates that the headwater streams of the Province are vulnerable to acidification. Total alkalinity and p11 were generally higher in third order reaches (mean, 72 μeq/θ and 6.7) than in first order reaches (64 μeq/θ and 6.4). Ionic concentrations were low, averaging 310 and 340 μeq/θ in first and third order reaches, respectively. A single sampling appears adequate for evaluating sensitivity based on total alkalinity, but large temporal variability requires multiple sampling for the detection of changes in pH and alkalinity over time. Monitoring of stream water should continue in order to detect any subtle effects of acidic deposition on these unique resource systems.     

HYDRODYNAMIC SIMULATIONS OF A CONSTRUCTED WETLAND IN SOUTH FLORIDA1

ABSTRACT: This paper describes the application of the SHEET2D model to the Florida's Everglades Nutrient Removal (ENR) Project. The ENR Project is a 3815 acre (1545 ha) pilot project, located in Palm Beach County. The operation of the treatment system will be used to demonstrate the performance of larger scale constructed wetland systems for removal of phosphorus from Everglades Agricultural Area (EAA) stormwater runoff. It is currently the largest stormwater wetland treatment system in the world. The SHEET2D model was used to analyze the performance of the ENR Project. SHEET2D is a two-dimensional, depth-averaged hydrodynamic model that is applicable to shallow water flow conditions. Subsequently, results from SHEET2D simulations were used to develop the ENEMOD model. ENRMOD is a lumped parameter box water quality model that can be used to analyze the long term performance of the ENR project with respect to hydrology and phosphorus uptake. Localized short-circuiting in the agricultural ditches within the project area was analyzed by using the RBFVM-2D model, which is a finite volume hydrodynamic model that is also applicable to shallow water flow conditions. The SHEET2D model was employed to simulate the hydraulics of the structures between cells and the hydrodynamics of the sheet-flow moving across the buffer cell and treatment cells. Collection, distribution, and larger discharge canals within the project were simulated by means of the MultiBasin Routing (MBR) model features that are built into the SHEET2D model. Constant inflows (75 to 600 cfs [2.1 to 17 m³/s]) were used in all runs to simulate the discharge of the ENR Project based on the proposed operating schedule for the outflow pump station. The model simulated 30 days to reach steady state conditions. Under steady state conditions, the hydraulic retention times were computed for the project and the split of flow between the two treatment trains of the entire project from the common buffer cell. Additionally, design components such as height of the levees, capacity of the structures, and hydrographs at specified grids were obtained.     

A TEST OF SEVERAL EVAPORATION EQUATIONS FOR WATER TEMPERATURE SIMULATIONS IN LAKES1

ABSTRACT: Evaporative heat loss is an essential component of any heat budget used for the modeling of lake water temperatures. Seven evaporative heat loss equations were tested in a year-round, physically-based temperature and dissolved oxygen model for lakes. Deciding which equation to choose for use in the year-round model was based on the goodness of fit of the simulated vs. measured surface temperatures, which were taken at a depth of 1 m below the water surface. An equation which includes free and forced convection components and which was previously used for cooling ponds gave the best fit between temperature simulations and measurements.     

GENERAL-CIRCULATION-MODEL SIMULATIONS OF FUTURE SNOWPACK IN THE WESTERN UNITED STATES1

ABSTRACT: April 1 snowpack accumulations measured at 311 snow courses in the western United States (U.S.) are grouped using a correlation-based cluster analysis. A conceptual snow accumulation and melt model and monthly temperature and precipitation for each cluster are used to estimate cluster-average April 1 snowpack. The conceptual snow model is subsequently used to estimate future snowpack by using changes in monthly temperature and precipitation simulated by the Canadian Centre for Climate Modeling and Analysis (CCC) and the Hadley Centre for Climate Prediction and Research (HADLEY) general circulation models (GCMs). Results for the CCC model indicate that although winter precipitation is estimated to increase in the future, increases in temperatures will result in large decreases in April 1 snowpack for the entire western U.S. Results for the HADLEY model also indicate large decreases in April 1 snowpack for most of the western US, but the decreases are not as severe as those estimated using the CCC simulations. Although snowpack conditions are estimated to decrease for most areas of the western US, both GCMs estimate a general increase in winter precipitation toward the latter half of the next century. Thus, water quantity may be increased in the western US; however, the timing of runoff will be altered because precipitation will more frequently occur as rain rather than as snow.     

A STOCHASTIC MODEL TO EVALUATE RIPARIAN IRRIGATION EXPANSION IN THE EASTERN UNITED STATES1

ABSTRACT: Irrigation has expanded in parts of the eastern United States. In some areas, the adjoining surface (riparian) water is the most economical source of irrigation water. Expanded demand for riparian water may lead to conflict among irrigators and other streamflow users. Accurate information on the potential for and impacts of riparian irrigation expansion is needed to decide if control of such expansion is necessary. In this study, a stochastic economic model to evaluate the impacts of potential irrigation expansion is presented. The model considers the soil, location, and land use characteristics of individual sites, as well as weather and streamflow patterns. The application of the model to an eastern Virginia watershed indicates that, with maximum potential expansion, water availability becomes limited and yields will be reduced in some years. As a result, the expected net returns from irrigation and the probability of breaking even on the investment are reduced substantially. The results suggest the need to consider regulation of surface water allocation for irrigation development in riparian watersheds.     

PHYTOPLANKTON IN THE FOX CHAIN OF LAKES1

ABSTRACT: As part of a comprehensive water quality investigation on the Fox Chain of Lakes during May to October 1975, water samples from the Chain and Cedar Lake (reference) at 25 locations were collected weekly or bi-weekly to determine the species and densities of algae. The results have been evaluated for algal composition, density, and succession for each location. Sixty-four algal species were recovered from 414 samples. The number of species per sampling location varied from 10 at Channel Lake and Lake Marie to 26 on Fox Lake (main) and Grass Lake. Blue green algae were predominant and occurred at 25 of the 25 sampling stations. They consisted mainly of Aphanizomenon flos-aquae. The only flagellate of importance was Ceratium hirundinella, and significant concentrations of this organism were limited to Channel Lake and Lake Catherine. The only green alga bloom was created by Ulothrix variabilis on the waters of Pistakee Lake. Diatoms were quite significant on the shallower water bodies. Algal densities ranged from about 25 to 14,000 cts/ml. The highest count occurred on Mineola Bay. Other high counts (>10,000 cts/ml) observed were waters taken from Channel Lake, Grass Lake, and Fox Lake (main). In Grass Lake, 60 percent of the collections had algal densities in excess of 2,000 cts/ml. Most of these were the diatom Cyclotella meneghiniana.     

GEOMETRIC VARIATIONS IN RESERVOIR WATER QUALITY1

ABSTRACT: In developing water quality models for lakes and reservoirs, the assumptions of one-dimensionality (i.e., water quality changes are significant only in one dimension – usually depth), as well as two-dimensionality (considering the length and depth of the water body), have been utilized to predict water quality. In both caws, the assumption of lateral homogeneity is made. A field study was undertaken to determine the change of water quality in the lateral dimension. The main study reservoir was Center Hill Lake in Middle Tennessee. Data were also obtained for Cherokee Lake in East Tennessee. Several water quality parameters (temperature, dissolved oxygen, pH, conductivity, and oxidation reduction potential) were analyzed over the length, breadth, and depth of these reservoirs from pre-stratification through post-stratification. The statistical and theoretical three-dimensional analysis showed the expected variation for each water quality parameter in each direction. The influence of the lateral dimension on water quality management and modeling was found to be negligible.     

PHYTOPLANKTON RESPONSES TO GROUND WATER ADDITION IN CENTRAL FLORIDA LAKES1

ABSTRACT: Phytoplankton were studied in lakes augmented with water from the Floridan aquifer and in control lakes. Augmented lakes exhibited enhanced phytoplankton diversity which was believed to be related to chemical changes in the lakes brought about as a result of ground water addition. In particular, elevated concentrations of inorganic carbon appeared to influence phytoplankton populations.     

INCREASED BASEFLOW IN IOWA OVER THE SECOND HALF OF THE 20TH CENTURY1

ABSTRACT: Historical trends in annual discharge characteristics were evaluated for 11 gauging stations located throughout Iowa. Discharge records from nine eight‐digit hydrologic unit code (HUC‐8) watersheds were examined for the period 1940 to 2000, whereas data for two larger river systems (Cedar and Des Moines Rivers) were examined for a longer period of record (1903 to 2000). In nearly all watersheds evaluated, annual base flow, annual minimum flow, and the annual base flow percentage significantly increased over time. Some rivers also exhibited increasing trends in total annual discharge, whereas only the Maquoketa River had significantly decreased annual maximum flows. Regression of stream discharge versus precipitation indicated that more precipitation is being routed into streams as base flow than as storm flow in the second half of the 20th Century. Reasons for the observed stream flow trends are hypothesized to include improved conservation practices, greater artificial drainage, increasing row crop production, and channel incision. Each of these reasons is consistent with the observed trends, and all are likely responsible to some degree in most watersheds.     

USING SOIL TEXTURE TO ESTIMATE SATURATED HYDRAULIC CONDUCTIVITY AND THE IMPACT ON RAINFALL-RUNOFF SIMULATIONS1

ABSTRACT: In this paper a new set of soil texture data is used to estimate the spatial distribution of saturated hydraulic conductivity values for a small rangeland catchment. The estimates of conductivity are used to re-excite and re-evaluate a quasi-physically based rainfall-runoff model. The performance of the model is significantly reduced with conductivity estimates gleaned from soil texture data rather than the infiltration data used in our previous efforts.     

PHYTOPLANKTON PRODUCTIVITY AND BIOMASS IN THE CHARLOTTE HARBOR ESTUARINE SYSTEM,FLORIDA1

ABSTRACT: Phytoplankton carbon-14 productivity at a depth of 50 percent of surface light and chlorophyll-α concentrations were measured every other month from November 1985 through September 1986 at 12 stations in the Charlotte Harbor estuarine system. Maximum productivity and chlorophyll-α concentrations occurred during summer or early autumn near the mouths of tidal rivers. Most of the variability in light-normalized productivity and chlorophyll-α could be attributed to two factors derived from Principal Component Analysis of ambient water-quality characteristics. One factor related to seasonal variability and the other to spatial variability. The seasonal factor incorporated the interaction of temperature and nutrients. The spatial factor incorporated the interaction of salinity, nutrients, and water color that resulted from the mixing of freshwater inflow and seawater. Although freshwater inflow increased the availability of nutrients in low salinity (less than 10‰) waters, the highly colored freshwater restricted light penetration and phytoplankton productivity. Maximum productivity and biomass occurred where color associated with the freshwater inflow had been diluted by seawater so that light and nutrients were both available. Concentrations of inorganic nitrogen were often at or below detection limit throughout most of the high salinity (greater than 20‰) waters of the estuary and was probably the most critical nutrient in limiting phytoplankton productivity.     

AN INTEGRATED APPROACH TO WATER RESOURCES DEVELOPMENT OF THE TEHRAN REGION IN IRAN1

ABSTRACT: In this paper, a system approach to water resources development in Tehran Metropolitan Area, with its complex system of water supply and demands, is discussed. Water resources in this region include water storage in the Lar, Latyan, and Karaj reservoirs, the Tehran aquifer, as well as water discharge in local rivers and in drainage channels (mainly supplied by urban runoff and wastewater). This study consists of three phases of long‐term water resources planning and management in the Tehran metropolitan area. In each phase, a different level of details among different components of the system is considered. In the first phase, optimal operating policies for Tehran reservoirs and a decision support system are developed. In the second phase, interactions between surface and ground water resources as well as surface runoffs and wastewater disposal in different subareas are investigated. The water table fluctuations as a result of implementing sewerage collection project was also simulated. In the last phase, long‐term scenarios for water resources and agricultural development in the Southern part of Tehran are defined, and the effects of each scenario on the quality and quantity of surface and ground water resources are studied.     

CHANGES IN WATER QUALITY IN THE NEWLY IMPOUNDED SUBTROPICAL FEITSUI RESERVOIR,TAIWAN1

ABSTRACT: Water quality and trophic conditions in the Feitsui Reservoir, a subtropical reservoir, were evaluated with data from a ten-year data base to depict the impacts of river impoundment upon the chemical and biological characteristics of a reservoir, and to discuss the effects of flushing rate on in-lake phosphorus concentrations and phytoplankton growth. The results of the investigation showed that during the incipient impounding period, the water quality in the Feitsui Reservoir was significantly affected by internal loadings from submerged vegetation and soil in the flooded area. Studies of the changes in phosphorus compounds indicated that total phosphorus concentration appeared to approach equilibrium after the seventh year of impoundment and that orthophosphate stabilized after the sixth year of impoundment. Concentrations of both phosphorus forms varied seasonally after attaining stability. Nitrogen compounds (NH₃-N, NO₃-N and NO₂-N) approached equilibrium within three years after impoundment. The seasonal variation in carbon was correlated to the number of phytoplankton. The mean value of the N:P mass ratio has remained over 110 since year seven of impoundment (1990), indicating that phosphorus constitutes the potential limiting nutrient in the growth of phytoplankton. The rapid flushing rate (132.11 and 110.43 yr^-1) in Feitsui Reservoir during the first and second impounding stages was a critical factor influencing the phytoplankton growth response to available nutrients.     

EVALUATION OF CURVE NUMBER PROCEDURES TO PREDICT RUNOFF IN GLEAMS1

ABSTRACT: Proper selection of curve number values will improve the capability of the SCS-Curve Number procedure in predicting runoff. Both CREAMS and GLEAMS models use the Smith and Williams (1980) approach of converting CNII (curve number value for average antecedent moisture conditions) into CNI (curve number value for dry antecedent moisture conditions) in calculating the soil retention parameter (S). CREAMS and GLEAMS have been found to under predict runoff because of the internal conversion of CNII to CNI. This study shows modifications of the GLEAMS model using CMI without converting it to CM and it also shows the seasonal curve number approaches with and without converting CNII to CNI. Results indicate that using CNII without internal conversion to CNI provides better runoff and erosion predictions than the original version of GLEAMS and versions with seasonal curve numbers when tested with four years of field data in the Coastal Plain physiographic region of Maryland.     

STREAM FLOW IN RELATION TO OHIA FOREST DECLINE ON THE ISLAND OF HAWAII1

ABSTRACT: Dieback of the ohia forest over a large part of the Hilo watershed and adjacent areas has resulted in a severe loss of the overstory crown component of the vegetation. The decline could cause serious damage to the watershed. To evaluate possible changes in conditions in the Hilo area since the decline began, stream flow, water quality, and precipitation data from 1929 to 1980 were collected and analyzed. The limited data available do not indicate that the ohia decline has resulted in a significant change in either annual stream flow or peak stream flow of a stream discharging from the ohia forest in the Hilo area. Suspended sediment production of two streams remains well within accepted levels as does the chemical makeup of components dissolved in the streams.     

VOTER REACTIONS TO THE 1976 WATER DEVELOPMENT AND QUALITY REFERENDA IN TEXAS1

ABSTRACT: Since 1957, Texans have had the opportunity to vote on eight referenda concerning the allocation of state funds for water resources development and the maintenance of water quality. In 1976, a water development amendment and a water quality amendment were presented simultaneously to the voters of Texas, affording a unique opportunity for electoral-geographic comparison of county-level returns on the two issues. In this paper, cartographic and statistical analyses of the county-level voting outcomes for each referendum are presented. In both cases, the referenda were supported by voters in water-deficient West Texas, especially those counties dependent on irrigated crop production. In contrast, urban voters and East Texans tended to oppose both amendments. However, support for the water quality amendment in the urbanized areas of Dallas-Fort Worth, Austin, and San Antonio enabled this amendment to pass statewide while its counterpart failed. The results highlight the importance of local differences in perceived water policy needs, and in doing so they illustrate that geographical anlaysis of returns from initiatives and referenda is a useful tool for understanding the locational conflicts underlying water resources and other policy efforts.     

USING WATER HYACINTH TO TREAT MUNICIPAL WASTEWATER IN THE DESERT SOUTHWEST1

ABSTRACT: Water hyacinth (Eichhornia crassipes L.) has shown to be effective in the treatment of municipal wastewater in a pilot study begun in January 1989 by the Pima County Wastewater Management Department and researchers associated with The University of Arizona's Office of Arid Lands Studies in the Sonoran Desert near Tucson. The influent pumped into the pilot facility's six raceways (ponds) typically has been treated secondary effluent diverted from a conventional treatment facility, although primary effluent from the same facility also has been treated. The Secondary Influent Treatment System has met the Arizona Department of Environmental Quality (ADEQ) tertiary standard for BOD₅ and TSS of 10 mg/l for every month of its operation since March 1990; the Primary Influent Treatment System met the ADEQ secondary standard for BOD₅ and TSS of 30 mg/1 for most of the 10 months it was in operation.