SALT TRANSPORT BY THE SOUTH PLATTE RIVER IN NORTHEAST COLORADO1

ABSTRACT: The salinity of the lower South Platte River in Colorado is characterized by plotting the average annual flow, total dissolved solids, and salt mass flow against distance along the stream. The plots show that salts are being leached from the irrigated lands above Greeley and are being deposited on the irrigated lands below Greeley. The salt deposition on the lower lands will result in their salination. The plots show also that fall and winter stream flows carry most of the salt loads. These fall and winter flows are stored in off stream reservoirs for use during the irrigation season. Therefore these salts are transferred to the lower irrigated lands where they accumulate. The salt balance for these lands can be improved by permitting the fall and winter flows to leave the basin, or by providing adequate land drainage coupled with supplemental irrigation water.     

USING COMPUTED STREAM FLOW IN WATERSHED ANALYSIS1

Modifications in the computed climatic water budget have made it possible to achieve good agreement between computed and measured stream flow on both a monthly and annual basis in basins without appreciable winter snow cover. Comparisons of computed and measured stream flow in 28 basins on the Delmarva peninsula show that for some basins the agreement is excellent (regression line essentially equals unity), for other basins the regression line has a slope of one but it is displaced above or below the y=x line, while for other basins, the slope of the regression line differs appreciably from unity. Study of the basins where agreement between computed and measured values is only fair to poor reveals that the patterns of disagreement can be used to provide information on the water holding capacity in the root zone of the soil, on the quantity of deep aquifer recharge within the basin, or on the effect of human modifications within the basin. The technique should also reveal the quantity of interbasin transfers or other consumptive uses within the basin. The water budget, thus, becomes a useful tool to study hydrologic characteristics or their changes over time within a basin.     

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.     

VARIABILITY IN ADJUSTMENT PREFERENCES TO GROUNDWATER DEPLETION IN THE AMERICAN HIGH PLAINS1

ABSTRACT: This paper explores the adjustments and institutions that residents of the American High Plains prefer in coping with the depletion of the High Plains (Ogallaia) aquifer. The authors identify 48 possible adjustments and report on public preferences for them as determined from a mail survey of 956 respondents in 14 counties. For purposes of analysis, the adjustments are categorized into five groups: user practices, management policies, financial incentives and disincentives, technological fixes, and other. Preferences were also determined among five levels of government to enforce each of the adjustments. Adjustments associated with user conservation practices were generally most preferred while financial incentives and disincentives were least favored. Local groundwater management agencies were the most favored level of institution to administer conservation adjustments followed by the state, county, and federal levels. The most preferred option for 20 adjustments was that no agency should be involved. Respondents in agriculturally related occupations showed less support for water conservation laws and gave greater acceptance to the continuance of existing methods. Irrigators viewed the increasing cost of lifting water as a more serious problem than the depletion of groundwater.     

FLOW ROUTING MODELS FOR STREAM SYSTEM STUDIES1

ABSTRACT. Studies to determine frequency characteristics of regulated streams at points within a stream system require the use of flow routing models. This study compares several different flow routing methods using data from six river reaches. Results indicate that approximate flow routing methods yield good flow estimates when compared with observed flows. The unit response method, recently introduced, performed as well as other approximate methods for all reaches studied and gave better results for reaches subject to power releases.     

WATER RESOURCES DEVELOPMENT IN THE MULLICA RIVER BASIN1

ABSTRACT: The potential withdrawal of water from the Mullica River-Great Bay Estuary is southern New Jersey prompted a joint study by biologists and engineers to determine the maximum supply of water that could be diverted from the basin without causing undue environmental impacts. The effect of removal of water from the basin over long periods of time was simulated by review of records of a severe drought. Based on analysis of streamflows and salinities during these drought conditions, minimum mean monthly streamflows were determined corresponding to the maximum salinities tolerable by the fish and shellfish communities, important sources of revenue and recreation in the region. A physically optimized, chance constrained linear programming model was developed for the conjunctive use of ground and surface waters. Adjusting water withdrawal from streamflow and groundwater sources according to physical and seasonal criteria would permit maximum use of the basin's resources, with no additional burden on the ecology of the estuary.     

STREAM TEMPERATURE UNDER AN INADEQUATE BUFFER STRIP IN THE SOUTHEAST PIEDMONT1

ABSTRACT: A paired watershed experiment on the southeastern Piedmont to determine the effect of clearcutting loblolly pine on water quantity, quality, and timing has shown that stream water temperatures we increased as much as 20°F even though a partial buffer strip of trees and shrubs were left in place to shade the stream. Water time minimum stream temperatures were lowered as much as 10°F by the same treatment. A stream temperature model now in use did not predict such elevated temperatures. The authors suggest that forest cover reductions in areas of gentle land relief may elevate the temperature of shallow ground water moving to the stream, even with a substantial buffer strip Ln place.     

SIMULATION AND DECISIONMAKING: THE PLATTE RIVER BASIN IN NEBRASKA1

Substantial conflict exists over water management and allocation in the Platte River Basin of Nebraska. An interdisciplinary computer simulation model, representing the water quantity, water quality, environmental, and economic dimensions of the conflict, was developed in order to analyze the tradeoffs among allocation scenarios. Most importantly, decisionmakers and interest groups were involved in model development. Simulation results for a base case and two scenarios are presented. One scenario favors protection of instream flow for wildlife; the other favors water diversions for agriculture. Impacts of the instream flow scenario, as measured by the amount of land irrigated, groundwater levels, the amount of wildlife habitat for cranes and catfish, and net agricultural benefits did not differ greatly from those of the base case. However, impacts of the diversion scenario were substantial. On the negative side, instream flows and wildlife habitat declined an average of 39 percent; while, on the positive side, groundwater levels and net agricultural benefits each increased 6 percent. The modeling process was successful insofar as it promoted an understanding among the highly diverse interest groups of the systems nature of the Basin. One agreement on a water diversion schedule among three of the parties has been reached, partly as a result of this process. More comprehensive compromises have not yet been forged. Our experience, however, indicates that modeling success at the policymaking level depends more on the extent to which the policymakers understand the model than it does on model sophistication.     

IRRIGATION AND GROUNDWATER DEPLETION IN CADDO COUNTY,OKLAHOMA1

ABSTRACT: Similar groundwater problems associated with the Ogallala in western Oklahoma are beginning to affect aquifers much farther east. A rapid decline in the water table has been detected in Caddo County, Oklahoma. Ninety-six percent of the groundwater resources used in Caddo County are used for irrigation. Severe consequences for farmers, especially peanut growers, are possible in the near future.     

STREAM PHOSPHORUS EXPORTS FROM WATERSHEDS WITH CONTRASTING LAND USES IN SOUTHERN ONTARIO1

: The export of dissolved molybdate reactive phosphorus (DMRP) from 22 watersheds in the Duffin Creek drainage basin near Toronto Ontario was measured over a 25-month period. The annual average loss varied from 0.027 to 2.11 kg P/ha. Phosphorus levels in a number of watersheds were strongly influenced by effluent from a sewage treatment plant which contributed about 68 percent of the annual DMRP input to Duffin Creek. An analysis of 12 watersheds which did not contain major point pollution sources revealed that DMRP concentration and losses had a significant positive correlation with crop area and a strong negative association with forest, abandoned farm land, and area of sand + sandy loam soils. The causal relationships underlying these simple correlations are difficult to evaluate because of considerable multicollinearity between land use, soil, and topographic variables. Analysis of a mass balance for the downstream reaches of Duffin Creek indicated that there was considerable retention of phosphorus in the river channel particularly during summer low flows.     

GROUND WATER AS A SOURCE OF NUTRIENTS AND ATRAZINE TO STREAMS IN THE SOUTH PLATTE RIVER BASIN1

ABSTRACT: Concentrations of nitrite plus nitrate, ammonia, orthophosphate, and atrazine were measured in streams and ground water beneath the streams at 23 sites in the South Platte River basin of Colorado, Nebraska, and Wyoming to assess: (1) the role of ground water as a source of nutrients and atrazine to streams in the basin, and (2) the effect of land-use setting on this process. Concentrations of nitrite plus nitrate, ammonia, orthophosphate, and atrazine were higher in ground water than in the overlying streams at 2, 12, 12, and 3 of 19 sites, respectively, where there was not a measurable hydraulic gradient directed from the stream to the ground water. Orthophosphate was the only constituent that had a significantly higher (p ≤ 0.05) concentration in ground water than in surface water for a given land-use setting (range land). Redox conditions in ground water were more important than land-use setting in influencing whether ground water was a source of elevated nitrite plus nitrate concentrations to streams in the basin. The ratios of nitrite plus nitrate in ground water/surface were were significantly lower (p ≤ 0.05) at sites having concentrations of dissolved oxygen in ground water ≤ 0.5 mg/L than at sites having dissolved oxygen concentrations ≥ 0.5 mg/L. Elevated concentrations of ammonia or atrazine in ground water occurred at sites in close proximity to likely sources of ammonia or atrazine, regardless of land-use setting. These results indicate that land-use setting is not the only factor that influences whether ground water is a source of elevated nutrient and atrazine concentrations to streams in the South Platte River Basin.     

NUTRIENT CONCENTRATIONS IN WASTEWATER TREATMENT PLANT EFFLUENTS,SOUTH PLATTE RWER BASIN1

ABSTRACT: Accurate data about nutrient concentrations in wastewater treatment plant effluents are needed for river basin water-quality studies. As part of the U.S. Geological Survey's National Water-Quality Assessment Program in the South Platte River Basin, nutrient data were requested from 31 wastewater-treatment plants located in the basin. This article describes the types of nutrient data available from the plants, examines the variability of effluent nutrient concentrations, and discusses methods for estimation of nutrient concentrations where data are lacking. Ammonia was monitored at 88 percent of the plants, nitrite plus nitrate was monitored at 40 percent of the plants, and organic nitrogen and phosphorus were monitored at less than 25 percent of the plants. Median total nitrogen concentrations and median total phosphorus concentrations were small compared to typical literature estimates for wastewater-treatment plants with secondary treatment. Nutrient concentrations in effluent from wastewater-treatment plants varied widely between and within plants. For example, ammonia concentrations varied as much as 5 mg/L during a day, as much as 10 mg/L from day to day, and as much as 30 mg/L from summer to winter within a plant. In the South Platte River Basin, estimates of median annual ammonia and nitrite plus nitrate concentrations can be improved based on plant processes; and nitrite plus nitrate and organic nitrogen concentrations can be estimated based on ammonia concentrations. However, to avoid large estimation errors, more complete nutrient data from wastewater-treatment plants are needed for integration into river basin water quality studies. The paucity of data hinders attempts to evaluate the relative importance of point source and nonpoint source nutrient loadings to rivers.     

PHOSPHORUS ASSIMILATION IN A STREAM SYSTEM OF THE LAKE OKEECHOBEE BASIN1

ABSTRACT: The ability to predict how streams and wetlands retain phosphorus (P) is critical to the management of watersheds that contribute nutrients to adjacent aquatic systems such as lakes. Field and laboratory experiments were conducted to determine the P assimilatory capacity of a stream (Otter Creek) in the Taylor Creek/Nubbin Slough Basin located north of Lake Okeechobee, Florida. Dominant soils in this basin are sandy Spodosols; landuse is primarily dairy farms and beef cattle pastures. Estimates of P assimilation show that sediments assimilate approximately 5 percent of the P load. Phosphorus assimilation rates in the stream were estimated using first-order relationships based on the total P concentration of the water column as a function of distance from the primary source. This method assumes minimal lateral inputs. Stream lengths required for one turnover in P assimilation were estimated to be in the range of 3–16 km. Laboratory studies using intact sediment cores indicated a P assimilation rate of 0.025 m day^?1, and equilibrium P concentration of 0.16 ± 0.03 mg L^?1 in the water column. Dissolved P concentration gradients in the sediments showed upward flux of P at water column P concentration of <0.16 mg L^?1. Approximately 56–77 percent of the P assimilated in the above-ground vegetation during active growth was released or translocated within six months of senesence, suggesting short-term storage in above-ground vegetation. Bottom sediments and recalcitrant detrital plant tissue provide for long-term P assimilation in the creek. Although stream sediments have the potential to adsorb P, high flow rate and low contact period between water and sediment limits this process.     

ADOPTION OF WATER-SAVING PRACTICES BY IRRIGATORS IN THE HIGH PLAINS1

ABSTRACT: The High Plains has been viewed as an immense garden because of its highly productive agricultural system based on irrigation. But there is concern that the aquifers are being depleted and that the region may be returning to its natural state of a vast shortgrass prairie. Efforts to avoid this scenario and to ensure continued survival of the integrated agribusiness economy focus on conserving water in irrigation. This paper examines the adoption of 39 water-saving practices for ten counties in Kansas, Nebraska, Oklahoma, and Texas. The frequency of adoption was estimated from a survey of 709 irrigators, and the variance was found primarily to be a function of location and secondarily to be influenced by number of wells, type of irrigation system, depth to water, age, and education. Locational differences remained strong even when the influence of secondary factors were controlled.     

PROBABILISTIC METHODS IN STREAM QUALITY MANAGEMENT1

ABSTRACT. Recent advances in water quality modelling have pointed out the need for stochastic models to simulate the probabilistic nature of water quality. However, often all that is needed is an estimate of the uncertainty in predicting water quality variables. First order analysis is a simple method of providing an estimate in the uncertainty in a deterministic model due to uncertain parameters. The method is applied to the simplified Streeter-Phelps equations for DO and BOD; a more complete Monte Carlo simulation is used to check the accuracy of the results. The first order analysis is found to give accurate estimates of means and variances of DO and BOD up to travel times exceeding the critical time. Uncertainty in travel time and the BOD decay constant are found to be most important for small travel times; uncertainty in the reaeration coefficient dominates near the critical time. Uncertainty in temperature was found to be a negligible source of uncertainty in DO for all travel times.     

FILTERING OF DISSOLVED OXYGEN DATA IN STREAM WATER QUALITY ANALYSIS1

ABSTRACT: In this study a set of equations was developed which can be used to separate the time varying effects from observed dissolved oxygen (DO) data. A steady state DO profile thus derived allows a reasonable stream stimulation such that both the model and the data used in its formulation do not contain DO due to biological activities. Biological DO production and consumption are complex phenomena. By excluding these highly variable processes, this method simplifies stream DO modeling considerably. The net oxygen input due to these processes exist only part of the day, but, in the stream waste assimilative capacity analysiis and waste load allocation, one would focus his attention on critical condition. Hence, unless the change of stream ecology is the main concern, it is desirable to formulate a stream water quality model without this time varying term.     

STREAM WASTE ASSIMILATIVE CAPACITY ANALYSIS USING REAERATION COEFFICIENTS MEASURED BY TRACER TECHNIQUES1

Atmospheric reaeration is a natural mechanism of oxygen transfer from the atmosphere to a water body. In practice, stream water quality models are developed with reaeration coefficients (K₂) estimated by predictive equations. This leads to uncertainties in modeling analysis because these equations are empirical in nature and may yield greatly different K₂ values for the same stream. Values of K₂ may be adjusted in model calibration, but unfortunately, values of other model parameters are no less easy to identify and require adjustment in model calibration as well. Therefore, validity of a stream model would be enhanced significantly if K₂ could be determined directly and reliably. In this research, values of K₂ in the Canandaiqua Outlet in Central New York have been measured by using a gas tracer method. A successful modeling analysis was conducted using these K₂ values. As a result, effluent limitations of several waste water discharges into the Outlet were established. It was concluded that field measurements of reaeration rate would improve modeling results significantly, and that the gas tracer method can be easily incorporated into intensive water quality surveys normally required for stream modeling.     

STREAM TEMPERATURE INCREASES AND LAND USE IN A FORESTED OREGON WATERSHED1

ABSTRACT: The Salmon Creek Watershed drains 325 km² of forested terrain in the Cascade Mountains of western Oregon. Over a 30–year period (from 1955 to 1984) average daily maximum and minimum stream temperatures, calculated from the 10 warmest days of each year, have risen 6°C and 2°C, respectively. In contrast, a small decrease in maximum air temperatures was found over the same period. Regression analysis indicated a highly significant (p < 0.01) relationship between a cumulative index of forest harvesting and maximum stream temperatures. Maximum temperatures also tended to increase for several years following major peak flow events. The interaction between harvest activity (logging and road construction), changing forest and riparian management practices and the occurrence of natural hydrologic events (peak flows and associated mass soil movements) tend to obscure specific cause-and-effect relationships regarding long-term changes in maximum stream temperature.     

EFFECTS OF NO-FLOW RIVER CONDITIONS ON THE PLATTE RIVER WELL FIELD1

ABSTRACT: Effects of no-flow river conditions on the quantity and quality of water in the Platte River well field of the City of Grand Island, Nebraska, were examined utilizing a finite-difference computer simulation model specifically developed for this well field. Results suggest that the effects of these no-flow periods on water quality may be most important. In particular, the no-flow periods eliminate the hydraulic barrier between the well field and an area north of the River that is contaminated with nitrate (concentrations in the 20 to 40 mg/1 NO₃-N range). They also change the direction and velocity of movement of the contaminated ground water. Simulation results indicate that contaminated ground water moves toward the well field with a velocity of 0.42 ft/d after 30 days of no-flow and 1.43 ft/d after 180 days of no-flow. Limiting no-flow conditions to 10 consecutive days would protect the well field.