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This study investigates the influence of climate change on groundwater availability, and thereby, irrigation across political boundaries within the US High Plains aquifer. A regression model is developed to predict changes in irrigation according to predicted changes in precipitation and temperature from a downscaled dataset of 32 general circulation models (GCMs). Precipitation recharge changes are calculated with precipitation-recharge curves developed for prognostic representations of precipitation across the Nebraska-Colorado-Kansas area and within the Republican River Basin focal landscape. Irrigation-recharge changes are scaled with changes in irrigation. The groundwater responses to climate forcings are then simulated under new pumping and recharge rates using a MODFLOW groundwater flow model. Results show that groundwater pumping and recharge both will increase and that the effects of groundwater pumping will overshadow those from natural fluctuations. Groundwater levels will decline more in areas with irrigation-driven decreasing trends in the baseline. The methodologies and predictions of this study can inform long-term water planning and the design of management strategies that help avoid and resolve water-related conflicts, enabling irrigation sustainability. [ABSTRACT FROM AUTHOR]

Summary The conventional numerical method is computationally intensive and prone to numerical noises for stream depletion analyses using MODFLOW. In this study, a new MODFLOW package has been developed to improve the computational efficiency and reduce the noises for each simulation. Using the assumption of unchanged flow coefficients between the baseline and scenario runs, the nonlinear groundwater flow system is linearized for solving the flow equations. The new package has been successfully applied to a regional groundwater model in Nebraska. The results show that the numerical noises, commonly identified in conventional approach, have been significantly reduced and a twenty-fold speedup has been achieved for a regional groundwater model in Nebraska. The results suggest this package can be adapted to be a component of optimization tools for water management scenario analyses especially when a large number of scenario model runs are involved. [ABSTRACT FROM AUTHOR]

Abstract: It is challenging to simulate stream-aquifer interactions for the wide channel streams with the existing stream routing packages of MODFLOW. To overcome this limitation, a Cross-Section streamflow Routing (CSR) package is developed to simulate the streamflow and the interaction between streams and aquifers for the stream with a width larger than the MODFLOW grid size. In the CSR package, streams are divided into stream segments which are formed by two consecutive cross-sections. A cross-section is described by a number of streambed points that determine the geometry and hydraulic properties of the streambed. The stream water depth and streamflow at the cross-sections are related by the Single Channel method, the Divided Channel method, a data table or a power function. A rapid algorithm is used to compute the submerged area of the MODFLOW grid. The streambed conductance of a grid cell is computed based on its submerged area, streambed hydraulic conductivity and thickness. Stream-aquifer seepage is subsequently estimated as the product of the streambed conductance and difference between the stream stage and groundwater hydraulic head. Stream-aquifer seepage is treated as lateral flow in the streamflow routing computation with the Muskingum-Cunge method or mass conservation method. A hypothetical problem is established to test the capabilities of the CSR package with steady- and transient-state models. The results compare favorably with the SFR2 package and the HEC-RAS model. However, significant difference in flood wave attenuation is observed between the CSR package and the SFR2 package. It proves that the CSR package is capable of simulating the variation of stream-aquifer interactions in both space and time efficiently. The CSR package represents a certain improvement over previous MODFLOW streamflow packages by providing the efficient cross-section based computation and the unique capability of simulating streambed heterogeneity in longitudinal and transverse directions. [Copyright &y& Elsevier]

Dependence on groundwater throughout the Central Valley of California has resulted in severe and unsustainable groundwater depletion. In this research, we used the Central Valley hydrologic model (CVHM) to model how crop types and drought scenarios impact groundwater storage throughout the Central Valley. Simulations that decreased the abundance of water-intensive crops, such as fruits and nuts, observed the largest recovery in groundwater storage. Two drought scenarios, which respectively decreased surface water availability by 25% and 75%, were also tested. Combined drought and crop type scenarios were explored to understand the relative influence of either surface condition on groundwater storage. The results showed that water-intensive crops can decrease groundwater storage by over 20 m under water deficit conditions, whereas water-saving crops can recover groundwater storage and alleviate the impact of droughts. This research suggests that under drought conditions, groundwater storage will decline substantially to compensate for the need of water-intensive crops due to loss of surface water. Policy and management implications from this research suggest decreasing water demands, such as decreasing crop water intensity, can mitigate groundwater depletion. [ABSTRACT FROM AUTHOR]

The article evaluates the Spreadsheet-Based MODFLOW Pre-Processor (SMPP).

Information on the anisotropy of streambed hydraulic conductivity ( K) is a necessity for analyses of water exchange and solute transport in the hyporheic zone. An approach is proposed for the determination of K, developed from existing in-situ permeameter test methods. The approach is based on determination of vertical and horizontal hydraulic conductivity of streambed sediments on-site and eliminates the effects of vertical flow in the hyporheic zone and stream-stage fluctuation, which normally influence in situ permeameter tests. The approach was applied to seven study sites on four tributaries of the Platte River in east-central Nebraska, USA. On-site permeameter tests conducted on about 172 streambed cores for the determination of vertical hydraulic conductivity ( K) and horizontal hydraulic conductivity ( K) at the study sites indicate that the study sites have relatively small anisotropic ratios, ranging from 0.74 to 2.40. The ratios of K to K from individual locations within a study site show greater variation than the anisotropic ratios from the mean or median K at each of the study sites. [ABSTRACT FROM AUTHOR]

Determination of the nature and extent of the connection between groundwater and surface water is of paramount importance to managing water supplies. The development of analyses that detail the surface water-groundwater system may lead to more effective utilization of available water. A tool was developed to help determine the effects of groundwater and surface water interactions. The software tool includes two graphic user interfaces to allow full compatibility with numerical MODFLOW groundwater models. This case study shows the tool, in conjunction with MODFLOW groundwater models and carefully designed scenarios, can successfully calculate the rates of stream-groundwater interactions, thereby providing the basis for designating management areas with the most significant hydrologic impact. This tool can be applied in other regions with similar settings and needs for integrated water management. [ABSTRACT FROM AUTHOR]

Summary The Platte River in south-central Nebraska is a priority reach to maintain appropriate in-stream flow for healthy stream habitat. Transmission losses normally take place here when flood wave or reservoir-release water travels through during summer and fall. However, it is found that the reservoir-release water hardly arrived at the habitat area due to the transmission losses. Meanwhile, the limited reservoir water also is critical for crop irrigations during the same season. Therefore, to reconcile the water requirement conflict, the knowledge of the temporal–spatial variations of the transmission losses along the river is necessary to better manage the released water. Two flood events, which were only generated by upstream rainstorms, traveled through the nearly non-flowing reach of the Platte River in south-central Nebraska during the summer of 2013. The hydrological records during the two flood events provided unique data sets to study the transmission losses in the reach. The objective of this study was to investigate the temporal–spatial variation of the transmission losses during the two flood events in the reach. A numerical–analytical transmission loss model was developed to support the analysis. The results indicated that the transmission loss process in the study reach would be reasonably simulated using an effective aquifer transmissivity value of 2000 m 2 /d and an effective stream leakance value of 600 1/d. About 52% and 21% of the stream water flowed into the reach became the transmission losses during the two flood events, respectively. The transmission losses significantly enhanced the stream stage attenuation during the two events. Due to the stream stage attenuation, the total transmission losses decreased linearly between the upstream and downstream gauges, but its detailed spatial variation can be documented based on further hydrogeological data collection along the reach. [ABSTRACT FROM AUTHOR]

Summary: Vertical hydraulic conductivities (Kv ) of both streambed and point bars can influence water and solute exchange between streams and surrounding groundwater systems. The sediments in point bars are relatively young compared to the older sediments in the adjacent aquifers but slightly older compared to submerged streambeds. Thus, the permeability in point bar sediments can be different not only from regional aquifer but also from modern streambed. However, there is a lack of detailed studies that document spatial variability of vertical hydraulic conductivity in point bars of meandering streams. In this study, the authors proposed an in situ permeameter test method to measure vertical hydraulic conductivity of the two point bars in Clear Creek, Nebraska, USA. We compared the Kv values in streambed and adjacent point bars through 45 test locations in the two point bars and 51 test locations in the streambed. The Kv values in the point bars were lower than those in the streambed. Kruskal–Wallis test confirmed that the Kv values from the point bars and from the channel came from two statistically different populations. Within a point bar, the Kv values were higher along the point bar edges than those from inner point bars. Grain size analysis indicated that slightly more silt and clay particles existed in sediments from inner point bars, compared to that from streambed and from locations near the point bar edges. While point bars are the deposits of the adjacent channel, the comparison of two groups of Kv values suggests that post-depositional processes had an effect on the evolution of Kv from channel to point bars in fluvial deposits. We believed that the transport of fine particles and the gas ebullition in this gaining stream had significant effects on the distribution of Kv values in a streambed-point bar system. With the ageing of deposition in a floodplain, the permeability of point bar sediments can likely decrease due to reduced effects of the upward flow and gas ebullition. [Copyright &y& Elsevier]

Abstract: The application of artificial neural network (ANN) to rainfall-runoff simulations has provided promising results in recent years. However, it is difficult to obtain satisfying results by using raw data for the direct prediction of the time series of streamflows. To improve simulating daily streamflow with back-propagation (BP) neural networks, the whole data set in this study is divided into two independent groups, flood period and non-flood period. The approaches and techniques of applying the division-based BP (DBP) in runoff simulation are presented in this paper. A comparison of the DBP model to the primitive BP model and the Xinanjiang model was also conducted to evaluate the effectiveness of the improvement. The numerical experimental results indicate that DBP model still overestimated flow peak, but improved considerably the streamflow simulation in the non-flood period. [Copyright &y& Elsevier]