Relationships between riparian evapotranspiration and groundwater depth along a semiarid irrigated river valley

Evapotranspiration (ET) from riparian vegetation can be difficult to estimate due to relatively abundant water supply, spatial vegetation heterogeneity, and interactions with anthropogenic influences such as shallower groundwater tables, increased salinity, and nonpoint source pollution induced by irrigation. In semiarid south-eastern Colorado, reliable ET estimates are scarce for the riparian corridor that borders the Arkansas River. This work investigates relationships between the riparian ecosystem along the Arkansas River and an underlying alluvial aquifer using ET estimates from remotely sensed data and modelled water table depths. Results from a calibrated, finite-difference groundwater model are used to estimate weekly water table fluctuations in the riparian ecosystem from 1999 to 2009, and estimates of ET are calculated using the Operational Simplified Surface Energy Balance (SSEBop) model with over 200 Landsat scenes covering over 30 km² of riparian ecosystem along a 70-km stretch of the river. Comparison of calculated monthly SSEBop ET to estimated alfalfa reference ET from local micrometeorological station data indicated statistically significant high linear correspondence (R² = .87). Daily calculated SSEBop ET showed statistically significant moderate linear correspondence with data from a local weighing lysimeter (R² = .59). Simulated monthly SSEBop ET values were larger in drier years compared with wetter years, and ET variability was also larger in drier years. Peak ET most commonly occurred during the month of June for all 11 years of analysis. Relationships between ET and water table depth showed that peak monthly ET was highest when groundwater depths were less than about 3 m, and ET values were significantly lower for groundwater depths greater than 3 m. Negative sample Spearman correlation highlighted riparian corridor locations where ET increased as a result of decreased groundwater depths across years with different hydroclimatic conditions. This study shows how a combination of remotely sensed riparian ET estimates and a regional groundwater model can improve our understanding of linkages between riparian consumptive use and near-river groundwater conditions influenced by irrigation return flow and different climatic drivers.     

Embedding isochronous cells overland flow module into MODFLOW

This study integrates a simple overland flow module (isochronous cells model) with the river module of MODFLOW such that temporal and spatial interactions between stream flow and groundwater can be simulated using net rainfall data of a watershed. The isochronous cells model is an efficient travel time runoff approach based on geographic information system (GIS) that considers both spatial and temporal variations of net rainfall through hill slope of the watershed. This overland module is easily coupled with MODFLOW river routing module. Specifically, the stream flow from the isochronous cells model is directly assigned to both sides of river cells of the MODFLOW model. Such an integration of MODFLOW and isochronous cells model is especially useful in watersheds where river flow data are limited. The feasibility of this integrated model was demonstrated using a case study in the middle and downstream regions of the Yitong River watershed, China. Copyright © 2012 John Wiley & Sons, Ltd.     

Comparing MODFLOW simulation options for predicting intra‐meander flux

During the evolution of meander bends, the intra‐meander groundwater head gradients steepen and generate zones of accelerated water and nutrient intra‐meander fluxes important for ecosystem processes. This paper compares and contrasts three MODFLOW groundwater model packages based on their simulation of intra‐meander flux for two stages of meander evolution observed in a sandbox river table and one level of river bed clogging, where the hydraulic conductivity in the river bed is lower than in the adjacent aquifer. These packages are the Time‐Variant Specified Head package [constant head (CHD)], River package (RIV), and Streamflow‐Routing package (SFR2), each controlling the groundwater or river head bounding the intra‐meander region. The RIV and SFR2 packages fix river stage and allow for variation in groundwater head below the river, which is suggested for simulating intra‐meander flux for all sinuosities with and without river bed clogging whenever river bed parameters are available. The CHD package fixes below river groundwater head and fails to simulate intra‐meander head loss and flux in meanders with high sinuosity or river bed clogging. In low sinuosity meanders and in cases without river bed clogging, there were no significant differences between MODFLOW packages for simulating river intra‐meander head loss and flux. This research demonstrates why MODFLOW users need to consider the limitations of each package when simulating intra‐meander flux in reaches with river bed clogging, high sinuosity, or similarly steep hydraulic gradients. Copyright © 2014 John Wiley & Sons, Ltd.     

地表水文过程与地下水动力过程耦合模拟及应用

地表水和地下水是水循环系统不可缺少的部分,对相互作用与反馈的模拟计算有助于水资源精准评价。在非饱和带数值计算模型(UZF1)与模块化地下水动力模型(MODFLOW2005)耦合的基础上构建了一个地表水文过程与地下水动力过程耦合数值模拟模型,模型可以同时输出流域出口断面流量和地下水位的空间分布,有利地提高了模型的可靠性。将模型应用于资料条件较好的临涣集流域,从模拟结果分析来看,模型可以很好地模拟流域出口流量与地下水位空间动态变化过程,具有较高的模拟精度。     

MODFLOW在新疆灌区地下水资源开发评价中的应用

为改善新和县灌区耕地农业用水季节性和高峰期水资源供需矛盾,保证农业经济可持续发展,对新和县旧灌区进行改造。结合新和县水文地质构造,利用MODFLOW软件,将2007年8月的流场作为规划年的初始流场,对新和县灌区地下水开采的三个方案进行数值模拟.模型运行后预报了各方案运行5年和10年后的水量和水位,分析出合理的灌区地下水资源开发方案,为科学合理的开发利用该区域地下水资源提供一条有效途径。     

MODFLOW在渗渠取水工程中的应用研究

安塞油田近几年产量不断攀升,给干旱少雨、地下水资源十分贫乏的安塞地区供水带来了很大困难。为满足采油厂的需水要求,需要对谭家营水源地的取水能力进行评估。水源地的取水工程拟采用渗渠取水方式。根据延河河谷区概况建立延河水资源数学模拟模型,使用MODFLOW计算模拟渗渠在不同设计方案下的取水量。通过对渗渠取水地区地下水补给量、河流径流量的分析,并和渗渠开采量进行比较,确定渗渠取水量1774m3／d是有保证的。     

注水试验与放水试验求取渗透系数的差异

基于矿井涌水量计算及水资源评价需要,本文运用注水试验代替抽水试验,求取了太原组灰岩含水层的渗透系数。根据后期同一含水层井下放水试验资料,利用VISUAL MODFLOW建立了水文地质三维非稳定流数值模型,通过分区拟合调参,获得了含水层分区水文地质参数。通过对这两种试验求得的渗透系数进行比较,得出在裂隙介质中注水试验是放水试验所得渗透系数值的35.6%~50.8%。建议在不具备进行抽（放）水试验的条件下,可使用注水试验代替,所得渗透系数值乘以校正系数,用校正后的渗透系数来计算矿井涌水量。     

A modelling study of hyporheic exchange pattern and the sequence,size, and spacing of stream bedforms in mountain stream networks,Oregon, USA

Studies of hyporheic exchange flows have identified physical features of channels that control exchange flow at the channel unit scale, namely slope breaks in the longitudinal profile of streams that generate subsurface head distributions. We recently completed a field study that suggested channel unit spacing in stream longitudinal profiles can be used to predict the spacing between zones of upwelling (flux of hyporheic water into the stream) and downwelling (flux of stream water into the hyporheic zone) in the beds of mountain streams. Here, we use two‐dimensional groundwater flow and particle tracking models to simulate vertical and longitudinal hyporheic exchange along the longitudinal axis of stream flow in second‐, third‐, and fourth‐order mountain stream reaches. Modelling allowed us to (1) represent visually the effect that the shape of the longitudinal profile has on the flow net beneath streambeds; (2) isolate channel unit sequence and spacing as individual factors controlling the depth that stream water penetrates the hyporheic zone and the length of upwelling and downwelling zones; (3) evaluate the degree to which the effects of regular patterns in bedform size and sequence are masked by irregularities in real streams. We simulated hyporheic exchange in two sets of idealized stream reaches and one set of observed stream reaches. Idealized profiles were constructed using regression equations relating channel form to basin area. The size and length of channel units (step size, pool length, etc.) increased with increasing stream order. Simulations of hyporheic exchange flows in these reaches suggested that upwelling lengths increased (from 2·7 m to 7·6 m), and downwelling lengths increased (from 2·9 m to 6·0 m) with increase in stream order from second to fourth order. Step spacing in the idealized reaches increased from 5·3 m to 13·7 m as stream size increased from second to fourth order. Simulated downwelling lengths increased from 4·3 m in second‐order streams to 9·7 m in fourth‐order streams with a POOL–RIFFLE–STEP channel unit sequence, and increased from 2·5 m to 6·1 m from second‐ to fourth‐order streams with a POOL–STEP–RIFFLE channel unit sequence. Upwelling lengths also increased with stream order in these idealized channels. Our results suggest that channel unit spacing, size, and sequence are all important in determining hyporheic exchange patterns of upwelling and downwelling. Though irregularities in the size and spacing of bedforms caused flow nets to be much more complex in surveyed stream reaches than in idealized stream reaches, similar trends emerged relating the average geomorphic wavelength to the average hyporheic wavelength in both surveyed and idealized reaches. This article replaces a previously published version (Hydrological Processes, 19 (17), 2915–2929 (2005) [ DOI:10.1002/hyp.5790 ]. See also retraction notice DOI:10.1002/hyp.6350 Copyright © 2006 John Wiley & Sons, Ltd.     

Application of an integrated surface water‐groundwater model to multi‐aquifers modeling in Choushui River alluvial fan,Taiwan

This research proposes a combination of SWAT and MODFLOW, MD‐SWAT‐MODFLOW, to address the multi‐aquifers condition in Choushui River alluvial fan, Taiwan. The natural recharge and unidentified pumping/recharge are separately estimated. The model identifies the monthly pumping/recharge rates in multi‐aquifers so that the daily streamflow can be simulated correctly. A multi‐aquifers condition means a subsurface formation composed of at least the unconfined aquifer, the confined aquifer, and an in‐between aquitard. In such a case, the variation of groundwater level is related to pumping/recharge activities in vertically adjacent aquifer and the river‐aquifer interaction. Both factors in turn affect the streamflow performance. Results show that MD‐SWAT‐MODFLOW performs better than SWAT alone in terms of simulated streamflow, especially during low flow period, when pumping/recharge rates are properly estimated. A sensitivity analysis of individual parameter suggests that the vertical leakance may be the most sensitive among all investigated MODFLOW parameters in terms of the estimated pumping/recharge among aquifers, and the Latin‐Hypercube‐One‐factor‐At‐a‐Time sensitivity analysis indicates that the hydraulic conductivity of channel is the most sensitive to the model performance. It also points out the necessity to simultaneously estimate pumping/recharge rates in multi‐aquifers. The estimated net pumping rate can be treated as a lower bound of the actual local pumping rate. As a whole, the model provides the spatio‐temporal groundwater use, which gives the authorities insights to manage groundwater resources. Copyright © 2012 John Wiley & Sons, Ltd.     

Understanding and modelling spatial drain–aquifer interactions in a low‐lying coastal aquifer—the Thurne catchment,Norfolk, UK

Seawater intrusion into fresh groundwater formations generally results inadvertently from human activities, such as over‐abstraction from coastal aquifers. This article describes the data analysis to quantify drain–aquifer interactions in a low‐lying pump‐drained coastal aquifer, which is subject to saline intrusion due to widespread land drainage, and the resulting development and application of a numerical groundwater model to understand the spatial groundwater system behaviour (including groundwater salinity fluxes). Without measured flow data in this pump‐drained catchment, a novel groundwater head‐dependent approach to hydrograph separation is described. Time‐variant and time‐invariant MODFLOW analyses are utilised to examine the flow processes. A new approach to calculate drain coefficients, which represent the extensive network of drainage ditches in the regional model, using field information, is described; the sum of the drainage coefficients are close to the values independently estimated from the head‐dependent hydrograph separation. Results show that (1) the groundwater flows into the drainage systems are well reproduced using the new drain coefficients, (2) particle tracking of fresh and saline water can explain observed spatial salinity distribution within drainage networks and (3) the modelled flow of seawater across the coast is approximately 25% greater than that discharged by the pumps, demonstrating the need for drainage management to be aware of the slow response of groundwater systems to past drainage system changes. The article demonstrates that numerical groundwater modelling can produce the improved understanding needed to inform management decisions in such complex environments. Copyright © 2010 John Wiley & Sons, Ltd.