A SIMPLE METHOD FOR ESTIMATING BASEFLOW AT UNGAGED LOCATIONS1

ABSTRACT: Baseflow, or water that enters a stream from slowly varying sources such as ground water, can be critical to humans and ecosystems. We evaluate a simple method for estimating base‐flow parameters at ungaged sites. The method uses one or more baseflow discharge measurements at the ungaged site and longterm streamflow data from a nearby gaged site. A given baseflow parameter, such as the median, is estimated as the product of the corresponding gage site parameter and the geometric mean of the ratios of the measured baseflow discharges and the concurrent discharges at the gage site. If baseflows at gaged and ungaged sites have a bivariate lognormal distribution with high correlation and nearly equal log variances, the estimated baseflow parameters are very accurate. We tested the proposed method using long‐term streamflow data from two watershed pairs in the Driftless Area of southwestern Wisconsin. For one watershed pair, the theoretical assumptions are well met; for the other the log‐variances are substantially different. In the first case, the method performs well for estimating both annual and long‐term baseflow parameters. In the second, the method performs remarkably well for estimating annual mean and annual median baseflow discharge, but less well for estimating the annual lower decile and the long‐term mean, median, and lower decile. In general, the use of four measurements in a year is not substantially better than the use of two.     

活性炭深度处理工艺用于地下回灌的水质研究

以北京高碑店污水处理厂二级生化出水为对象,研究了用于地下回灌的活性炭三级处理工艺.活性炭可有效降低DOC,UV-254和COD,部分去除可吸附有机卤化物(AOX).再经过土壤含水层处理,约90%的可吸附有机溴化物(AOBr)可被去除.Ames试验结果显示活性炭工艺可有效降低二级生化出水中的致突物.GC/MS分析表明,活性炭吸附可降低有机物含量,再经土壤含水层处理,大部分有机物及优先控制的污染物可被去除.      

EFFECTS OF TOPOGRAPHY AND SOIL PROPERTIES ON RECHARGE AT TWO SITES IN AN AGRICULTURAL FIELD1

ABSTRACT: Field experiments were conducted from 1992 to 1995 to estimate ground water recharge rates at two sites located within a 2.7‐hectare agricultural field. The field lies in a sand plain setting in central Minnesota and is cropped continuously in field corn. The sites are located at a topographically high (upland) site and a topographically low (lowland) site in an effort to quantify the effects of depression focusing of recharge. Three site‐specific methods were used to estimate recharge rates: well hydrograph analysis, chlorofluorocarbon age dating, and an unsaturated zone water balance. All three recharge methods indicated that recharge rates at the lowland site (annual average of all methods of 29 cm) exceeded those at the upland site (annual average of 18 cm). On an annual basis, estimates by the individual methods ranged from 12 to 44 percent of precipitation at the upland site and from 21 to 83 percent at the lowland site. The difference in recharge rates between the sites is primarily attributed to depression focusing of surface water runon at the lowland site. However, two other factors were also important: the presence of thin lamellae at the upland site, and coarser textured soils below a depth of 1.5 m at the lowland site.     

FROZEN SOIL IMPACT ON GROUND WATER‐SURFACE WATER INTERACTION1

ABSTRACT: Ground water and surface water interaction in the prairie pothole region of the United States and Canada is seasonally dominated by the presence of thick, frozen soil layers that affect infiltration. During a spring thaw, the subsoil may remain frozen, preventing infiltration. The impact of the frozen soil layer on the timing of infiltration of depressional‐focused recharge to the ground water is not clearly understood. The objective of this paper is to relate changes in the water table during spring to changes in frost depth and soil water content. A depression and adjacent upland study site were instrumented with CRREL‐type frost tubes, neutron probe access tubes, and ground water monitoring wells. Increases in water table levels in a depression occurred before the frost layer decomposed and infiltrating water quickly formed a recharge mound. Water table responses at the upland site took place as two events. The first event was a gradual rise, probably caused by the lateral dissemination of the recharge mound. The second rise was a rapid rise coinciding with the decomposition of the soil frost layer. Because of the accumulation of surface water in depressions, agricultural practices that remove water from a field can affect water resources management by limiting the addition of water recharge to unconfmed ground water.     

Impacts of Variable Climate and Effluent Flows on the Transboundary Santa Cruz Aquifer

Assessing groundwater resources in the arid and semiarid borderlands of the United States and Mexico represents a challenge for land and water managers, particularly in the Transboundary Santa Cruz Aquifer (TSCA). Population growth, residential construction, and industrial activities have increased groundwater demand in the TSCA, in addition to wastewater treatment and sanitation demands. These activities, coupled with climate variability, influence the hydrology of the TSCA and emphasize the need for groundwater assessment tools for decision‐making purposes. This study assesses the impacts of changes in groundwater demand, effluent discharge, and climate uncertainties within the TSCA from downstream of the Nogales International Wastewater Treatment Plant to the northern boundary of the Santa Cruz Active Management Area. We use a conceptual water budget model to analyze the long‐term impact of the different components of potential recharge and water losses within the aquifer. Modeling results project a future that ranges from severe long‐term drying to positive wetting. This research improves the understanding of the impact of natural and anthropogenic variables on water sustainability, with an accessible methodology that can be globally applied.     

Effective Transboundary Aquifer Areas: An Approach for Transboundary Groundwater Management

The natural complexity, heterogeneity, and extent of transboundary aquifers around the world, have led to controversy over which method or criteria should be used to identify and delineate their boundaries. Currently, there is no standard methodology that aquifer‐sharing countries can use to delineate the area of a transboundary aquifer. In the case of Mexico and Texas, Mexico uses administrative boundaries, whereas Texas uses geological boundaries. This paper proposes a method for delineation and prioritization of aquifers (or aquifer areas) called effective transboundary aquifer areas (ETAAs), which uses a combination of physical criteria (geological boundaries, topography, and hydrography) and the location and density of active water wells in the borderland between Mexico and Texas. This method identifies the area of priority (productivity area) in the aquifer using pumping patterns or hot spots regardless of the aquifer’s surficial geological limits, therefore offering a more effective, local and practical management option at the transboundary level. Different geological features or pumping patterns will have different sizes and locations of ETAAs within the same aquifer. In West Texas, which is dominated by bolsons, the method produces limited options for ETAAs, whereas in South Texas in the easternmost border the identified ETAAs are more significant.     

Analyzing the Effects of Groundwater Pumping on an Urban Stream‐Aquifer System

When the cone of influence of a pumping well reaches a nearby river, the resulting hydraulic gradient can induce enhanced seepage of streamflow into the aquifer. The rate of seepage is often modeled using analytical solutions that are simple to apply but may not reproduce field data due to mathematical assumptions not being met in the field. Furthermore, the appropriateness of such models has not been investigated in detail due to difficulty in measuring streamflow loss in the field. In this study, a field experiment was conducted on a reach of the South Platte River near Denver, Colorado to estimate pumping‐induced streamflow loss. A network of stream gauges, monitoring wells, and in situ measurements was used to observe streamflow rates, groundwater levels, and temperature to assess if pumping wells have a significant impact on streamflow, and to compare observed streamflow depletion against analytical solutions. Data collected suggest that pumping wells have a noticeable impact on streamflow. The analytical solutions proved accurate if streamflow was low and constant but performed poorly if streamflow was high and variable. Therefore, for this reach, the use of analytical solutions to predict streamflow may only be appropriate under low‐flow, constant‐flow conditions. Methods and results can be used to guide other streamflow depletion studies and to inform cases of pumping‐induced streamflow depletion, particularly in regard to water rights.     

IMPACT OF IRRIGATION WELLS ON BASEFLOW OF THE BIG BLUE RWER,NEBRASKA1

ABSTRACT: The Kansas-Nebraska Big Blue River compact requires that the state of Nebraska insure a minimum flow of the Big Blue River across the state line. There are two options that the state of Nebraska may use to ensure minimum flows. The obvious option is to limit surface-water irrigators along the river. However, under the terms of the compact, a second option may be to regulate irrigation wells that are within one mile of the river and were installed after November 1, 1968. The objective of this study is to quantify the effects of 17 irrigation wells that may be regulated on baseflow of the Big Blue River. A finite-element model is used to study the hydrogeologic system between DeWitt and Beatrice, Nebraska. The 17 wells that may be regulated are located between these towns and are developed in sediments deposited in a cross-cutting paleovalley anchor alluvium associated with the Big Blue River. While there wore considerable existing data, additional data were gathered by drilling an additional nine test holes, conducting several aquifer tests, stream-stage measurements, and baseflow calculation through extensive stream-discharge measurements, establishment of a ground water-level monitoring network, determining the amount of water pumped for irrigation and municipal use in the area, and a short-term precipitation network. The model was calibrated using observed baseflow and ground water level data. The model clearly shows that regulating the 17 wells to maintain baseflow would have a minimal effect on the overall water budget. This is reasonable, especially considering that there are over 250 irrigation wells in the project area. The 17 wells considered pumped only 6 percent of the total pumpage within the modeled area during the irrigation season of 1984. The computer model provides the documentation needed to demonstrate this fact. Although much of the resources spent and a significant amount of hydrogeologic data are being collected over a period of three years on a relatively small area, the simulation model could be improved through further field testing of the aquifer and stream-bed sediment characteristics and quantification of ground water recharge, discharge, and evapotranspiration rates.     

AQUIFER PARAMETERS FROM CONSTANT DRAWDOWN NONSTEADY-LEAKY TYPE CURVES1

ABSTRACT: A drain function and set of type curves were defined for the mathematical solution that represents one-dimensional flow under nonsteady conditions in a leaky aquifer for the constant drawdown boundary condition. A match point procedure was developed for determining the aquifer parameters transmissivity, storage coefficient, and leakance based on the drain function and type curves. Use of the procedure is illustrated by an example that utilizes simulated aquifer drawdowns and flowrate data. The drain function and type curves developed in this investigation include the effects of leakage for the constant drawdown boundary condition, which is not included in the existing drain function and type curve found in the literature. Thus, a new set of type curves was developed that can be used to analyze drawdowns for one-dimensional flow in a leaky aquifer with constant drawdown at a line sink. Applications would include flow to a canal or river, drainage of agricultural lands, and dewatering associated with strip mining operations.     

岩溶裂隙含水层中石油类污染物的迁移与水力截获

对淄博市岩溶地下水遭受石油类污染的研究结果表明，在石灰岩含水层中，岩溶裂隙的发育对石油类污染物侵入地下水的运移过程具有控制作用，石油类污染物沿岩溶裂隙通道运移，在通道延伸的深部可以有高于浅层的检出，水力截获方法去除地下水中石油类污染物是有效的，但水力截获孔的位置应就近污染物集中检出带布置，尽量远离水源地，并正常运行。