Development and application of a modeling approach for surface water and groundwater interaction

Investigation of the interaction of surface water (SW) and groundwater (GW) is critical in order to determine the effects of best management practices (BMPs) on the entire system of water resources. The objective of this research was to develop a modeling system for considering SW–GW interactions and to demonstrate the applicability of the developed system. A linked modeling approach was selected to consider SW–GW interaction. The dual-simulation scheme was developed to consider different time scales between a newly developed surface model: Dynamic Agricultural Non-point Source Assessment Tool (DANSAT), and existing groundwater models; a three-dimensional finite-difference groundwater flow model (MODFLOW) and a modular three-dimensional transport model (MT3D). A distributed and physically based DANSAT predicts the movement of water and pesticides in runoff and in leachate at a watershed scale. MODFLOW and MT3D simulate groundwater and pesticide movement in the saturated zone. Only the hydrology component of the linked system was evaluated on the QN2 subwatershed in the Nomini Creek watershed located in the Coastal Plain of Virginia mainly due to lack of observed data for MT3D calibration. The same spatial scale was used for both surface and groundwater models while different time scales were used because surface runoff occurs more quickly than groundwater flow. DANSAT and MODFLOW were separately calibrated using the integrated GW approach which uses own lumped baseflow components in DANSAT, and using the steady-state mode in MODFLOW, respectively. Then the linked system was applied to QN2 based on the parameters selected for DANSAT and MODFLOW to simulate time-dependent interactions on the entire system. The linked approach was better than the integrated approach for predicting the temporal trends of monthly runoff by improving the monthly Nash–Sutcliffe efficiency index from 0.53 to 0.60. The proposed linked approach will be useful for evaluating the impacts of agricultural BMPs on the entire SW–GW system by providing spatial distribution and temporal changes in groundwater table elevation and enhancing the reliability of calibrated parameter sets.     

基于SWAT模型的沂蒙山水土流失治理区地表水与地下水转化规律研究

为研究沂蒙山水土流失治理区,气候及植被覆盖变化影响下,水资源转化规律,以蒙阴县岸堤水库控制流域为研究对象,采用归一化植被指数(NDVI)为指标,分析植被覆盖的时空变化规律,采用分布式水文模型SWAT研究流域水文要素的时空演变规律,定量分析地表水与地下水转化量.计算结果表明:2000-2016年,流域NDVI呈增大趋势,...     

Combining hydrological modeling and GIS approaches to determine the spatial distribution of groundwater recharge in an arid irrigation scheme

Accurate quantification of the rate of groundwater (GW) recharge, a pre-requisite for the sustainable management of GW resources, needs to capture complex processes, such as the upward flow of water under shallow GW conditions, which are often disregarded when estimating recharge at a larger scale. This paper provides (1) a method to determine GW recharge at the field level, (2) a consequent procedure for up-scaling these findings from field to irrigation scheme level and (3) an assessment of the impacts of improved irrigation efficiency on the rate of GW recharge. The study is based on field data from the 2007 growing season in a Water Users Association (WUA Shomakhulum) in Khorezm district of Uzbekistan, Central Asia, an arid region that is characterized by a predominance of cotton, wheat and rice under irrigation. Previous qualitative studies in the region reported irrigation water supplies far above the crop water requirements, which cause GW recharge. A field water balance model was adapted to the local irrigation scheme; recharge was considered to be a fraction of the irrigation water losses, determined as the difference between net and gross irrigation requirements. Capillary rise contribution from shallow GW levels was determined with the HYDRUS-1D model. Six hydrological response units (HRUs) were created based on GW levels and soil texture using GIS and remote sensing techniques. Recharge calculated at the field level was up-scaled first to these HRUs and then to the whole WUA. To quantify the impact of improved irrigation efficiency on recharge rates, four improved irrigation efficiency scenarios were developed. The area under cotton had the second highest recharge (895 mm) in the peak irrigation period, after rice with 2,514 mm. But with a low area share of rice in the WUA of <1 %, rice impacted the total recharge only marginally. Due to the higher recharge rates of cotton, which is grown on about 40 % of the cropped area, HRUs with a higher share of cotton showed higher recharge (9.6 mm day^?1 during August) than those with a lower share of cotton (4.4 mm day^?1). The high recharge rates in the cotton fields were caused by its water requirements and the special treatment given to this crop by water management planners due to its strategic importance in the country. The scenario simulations showed that seasonal recharge under improved irrigation efficiency could potentially be reduced from 4 mm day^?1 (business-as-usual scenario) to 1.4 mm day^?1 (scenario with maximum achievable efficiency). The combination of field-level modeling/monitoring and GIS approaches improved recharge estimates because spatial variability was accounted for, which can assist water managers to assess the impact of improved irrigation efficiencies on groundwater recharge. This impact assessment enables managers to identify options for a recharge policy, which is an important component of integrated management of surface and groundwater resources.     

基于LU-SWAT模型的土地利用/覆被变化对水文过程的影响研究——以黑河上游为例

【目的】揭示内陆河流域集水区土地利用/覆被变化对水文过程的影响及其成因。【方法】基于能够逐年调用土地利用/覆被数据的LU-SWAT模型,并结合控制变量法研究了黑河流域集水区黑河上游1990—2009年土地利用/覆被变化对地表径流、侧向流、蒸散发量、地下径流以及总产水量的影响。【结果】LU-SWAT模型对于黑河上游月、年出山径流模拟结果较好,其月径流模拟的纳什系数为0.93,相关性系数为0.94;其年径流模拟的纳什系数为0.83,相关性系数为0.86。此外,其对各个水文要素的模拟结果符合西北干旱区内陆河流域集水区的水文特征;1990—2001年黑河上游土地利用变化主要表现在林地的减少,而2002—2009年土地利用的变化除了林地和草地的增加之外,还表现在裸地的大面积减少;1990—2001年黑河上游地表径流、侧向流、蒸散发量以及总产水量都呈现增加趋势,而地下径流呈减少趋势,2002—2009年流域地表径流、侧向流、蒸散发量以及总产水量减少,而地下径流量增加。在黑河上游,干旱条件下各水文要素对于土地利用覆被变化的响应更明显。【结论】1990—2001年林地的减少可能是流域地表径流、侧向流、蒸散发量以及总产水量都呈现增加趋势而地下径流呈减少趋势的主要原因。2002—2009年裸地的大面积减少可能是流域地表径流、侧向流、蒸散发量以及总产水量减少而地下径流量增加的主要原因。     

Groundwater recharge under alkali soils during reclamation

Reclamation of alkali soils modifies the water balance of an area. Hydrologically the soils under reclamation remain in a transient state over a long period of time because of the progressive improvement in their physio-chemical properties. The major component of the water balance that undergoes change is the groundwater recharge from crop land. A procedure to estimate the rate of change in recharge from crop land is presented and applied to typical alkali conditions in the command area of the Western Jamuna Canal.The value of groundwater recharge from this composite watershed, having normal and alkali soils in the ratio of 70 to 30, respectively, shows an increase of about 17.5% of the recharge value before reclamation for the optimal cropping patterns over a period of 20 years.     

A tool for community-based assessment of the implications of development on water security in hillside watersheds

Development and population growth in Latin American countries with steep slope farming are likely to further increase pressures on water and land resources. A methodology was developed for assessing water availability and use under different development pathways at a watershed scale to determine whether water security is a potential problem, and if so, under what conditions it is likely to occur. This methodology makes use of a GIS-based spatial water budget model for simulating stream water availability, water use and stream flow control on a daily basis at a watershed scale. Here, we analysed water availability under three plausible development scenarios for the 3246 ha Cabuyal River watershed in southwest Colombia in the year 2025: Corporate Farming (CF), Ecological Watershed (EW), and Business as Usual (BU). Simulated average river flows at the watershed outlet were, respectively, 874, 796 and 925 l s⁻¹ for the CF, EW and BU scenarios. The contribution of base flow to river flow (base flow index) was on average, 80.8, 85.6 and 77.9%, respectively, for the three scenarios. The watershed had the potential to meet the anticipated increase in water use under each explorative scenario. However, dams were necessary to store irrigation water in the CF scenario, otherwise over 60% of the available water would have been used during the dry season. Such a high figure raises concerns about effects on aquatic and riparian ecology, concentrations of potential contaminants, water reserves for especially low rainfall years, and the watershed resilience to meet temporarily higher water needs during the day. Analyses indicated that current water-use conflicts in the watershed can be resolved if irrigation water supply is separated from drinking water supply. This study helped reduce some of the complexity associated with the interdependencies between land and water resources, the impact of using them, and spatial linkages within the watershed. Results of this study can be used for teaching local stakeholders about basic landscape responses and helping multi-institutional alliances to become proactive and to guide development to the benefit of local communities.     

Impacts of water saving on groundwater balance in a large-scale arid irrigation district,Northwest China

Water saving practices are essential for sustainable use of water resources in semiarid regions. To understand the impacts of different water saving measures on groundwater resources, the Hetao Irrigation District in Northwest China was chosen in this study. Based on the data from 1991 to 2010, a groundwater balance model was calibrated and validated. The simulation results showed that irrigation-induced infiltration (92 % of the total groundwater recharge) and groundwater evaporation (92 % of the total groundwater discharge) were the primary factors controlling groundwater table fluctuations during irrigation seasons. The impacts of different water saving scenarios on groundwater balance components were then evaluated. The results revealed that the conjunctive use of water resources was the most effective way to improve water use efficiency (reducing surface water diversions by 52 %) and the depth to groundwater table increased by up to 79 cm. However, deeper groundwater tables may have a negative effect on crop growth due to reduced upward fluxes of groundwater into root zones. Therefore, future studies are needed to evaluate the impacts of different water saving measures on both water resources and crop yields. The results of this study provide further insights into effectively managing water resources in water-limited agricultural areas.     

环境变化对河北省水资源量的影响

分析了气候变化、地下水超采、地表径流及粮食产量变化等方面对水资源的影响，结论认为，在新一轮水资源评价中，要充分考虑环境变化对水资源量的影响，加强地下水位大埋深条件下地表产流量、地下水补给量以及作物产量水平提高对水资源影响的实验研究，以提高新一轮水资源评价成果的精度。     

基于SWAT模型的开都河上游未来土地利用变化对径流的影响

【目的】揭示土地利用变化下的流域径流变化。【方法】以开都河上游区域为研究对象,利用分布式水文模型SWAT,采用元胞自动机-马尔科夫模型(CA-Markov)预测法、当地土地利用规划要求和极端土地利用情景法共设置了4种2025年土地利用情景,包括自然发展情景、规划发展情景、极端草地情景、极端林地情景。【结果】①构建的SWAT模型在率定期(R2=0.74,NSE=0.73)与验证期(R2=0.58,NSE=0.57)的模拟结果可以接受。②采用CA-Markov模型模拟的2010年土地利用类型图Kappa系数为0.83,可用于预测2025年土地利用类型。1980—2010年土地利用类型变化主要表现为草地转换为水体和未利用地,其转换面积分别为106.09 km2和0.5 km2。③相较于基准年2010年,各土地利用情景下的年均径流量均减少,自然发展情景减少最快,极端草地情景减少最慢;从丰水期与枯水期来看,2种时期下各情景月均径流变化完全相反;从其季节分配来看,各土地利用类型在夏季对径流变化影响最大,冬季影响较小。【结论】该地区草地是影响径流最主要的调控因子,原有草地的减少会引起夏季径流较大幅度减少,对于未利用地,可考虑开发为草地。     

新疆平原区地下水资源评价误差来源分析

分析了新疆平原区地下水补给量、排泄量和可开采量评价的误差来源．提出了减少评价误差的措施：一是地下水动态监测和水运行测量统计是实现逐步逼近地下水资源量的最有效方法；二是加强基本水文及水文地质参数的试验研究；三是地下水资源评价要有动态的观念；四是建立地下水可开采量与当地地表水资源量、水利化标准间的关系：五是利用遥感技术确定土地利用现状等。     

沉降中心减采对北京平原地下水利用的影响分析

【目的】研究沉降中心减采对北京平原地下水利用的影响。【方法】采用非稳定流地下水模型和情景分析的方法,通过设计4个情景(现状保持(情景BAU)、沉降中心完全停采(情景PR100)、沉降中心减采50%(情景PR50)及沉降中心不同地区减采不同比例(情景PR520))模拟了地下水减采的影响。【结果】预测期内平均来说,情景BAU消耗1.16亿m3/a的含水层储存量,而情景PR100、PR50和PR520的储存量恢复分别为3.52亿、1.18亿和2.83亿m3/a。设计满足控沉目标的情景R:八仙庄、天竺和王四营用于工业和生活的地下水分别减采0.51亿、0.12亿和1.76亿m3,总开采量19.28亿m3,R是满足地面沉降控制要求条件下北京平原应采取的开采情景。【结论】沉降中心减采能有效恢复北京平原地下水水位和含水层储存量,是解决北京市地下水严重超采及其带来的地面沉降等生态环境问题最直接有效的方法,但要合理确定减采的比例,保证社会经济和地下水的协调发展。     

Sensitivity of groundwater recharge under irrigated agriculture to changes in climate, CO2 concentrations and canopy structure

Estimating groundwater recharge in response to increased atmospheric CO₂ concentration and climate change is critical for future management of agricultural water resources in arid or semi-arid regions. Based on climate projections from the Intergovernmental Panel on Climate Change, this study quantified groundwater recharge under irrigated agriculture in response to variations of atmospheric CO₂ concentrations (550 and 970 ppm) and average daily temperature (+1.1 and +6.4 °C compared to current conditions). HYDRUS 1D, a model used to simulate water movement in unsaturated, partially saturated, or fully saturated porous media, was used to simulate the impact of climate change on vadose zone hydrologic processes and groundwater recharge for three typical crop sites (alfalfa, almonds and tomatoes) in the San Joaquin watershed in California. Plant growth with the consideration of elevated atmospheric CO₂ concentration was simulated using the heat unit theory. A modified version of the Penman-Monteith equation was used to account for the effects of elevated atmospheric CO₂ concentration. Irrigation amount and timing was based on crop potential evapotranspiration. The results of this study suggest that increases in atmospheric CO₂ and average daily temperature may have significant effects on groundwater recharge. Increasing temperature caused a temporal shift in plant growth patterns and redistributed evapotranspiration and irrigation water use earlier in the growing season resulting in a decrease in groundwater recharge under alfalfa and almonds and an increase under tomatoes. Elevating atmospheric CO₂ concentrations generally decreased groundwater recharge for all crops due to decreased evapotranspiration resulting in decreased irrigation water use. Increasing average daily temperature by 1.1 and 6.4 °C and atmospheric CO₂ concentration to 550 and 970 ppm led to a decrease in cumulative groundwater recharge for most scenarios. Overall, the results indicate that groundwater recharge may be very sensitive to potential future climate changes.     

Environmental and economic impacts of reducing total phosphorous runoff in an agricultural watershed

The economy of northwest Arkansas relies greatly upon livestock and poultry production. The supply of production by-products is increasingly coming under scrutiny as an important source of water pollution in the region. This study uses stochastic dominance techniques to evaluate, environmentally and economically, a range of ten best management practice scenarios to lessen water pollution in the Lincoln Lake watershed. The goal is to generate rankings that could be useful for supporting producers’ and watershed managers’ selection of management practices to reduce total phosphorous losses in runoff. Specifically, this study compares scenarios in terms of net return risk reduction for bermudagrass hay producers.The results showed that environmental and economic rankings differ from each other. Although all scenarios analyzed were effective in reducing total phosphorous losses when compared to a baseline, six of them also decreased net returns. This suggests that including some best management practices may lead to increased net return risk. However, some scenarios were identified that may increase net returns, reduce total phosphorous losses and do not differ considerably from producers’ current management practices.The previous results suggested that the joint environmental-economic impact was important when considering scenarios and that producers’ risk attitudes and best management practices’ economic impacts should be accounted for when selecting scenarios. Producers and watershed managers can weigh trade-offs between total phosphorous losses reduction and net returns variability when making water conservation decisions.     

易引起地下水浅埋农田涝渍的降水过程分析

较多的降水往往会导致地下水浅埋区农田发生涝渍危害,结合湖北四湖流域实际,分析了可引起农田涝渍危害的降水过程特点,提出了致渍型、致涝型和涝渍相随型降水的概念。分析表明,50 mm以上的降水过程多出现在5月上旬和6月下旬,平均2.6~2.9年出现1次,降水持续时间主要在7 d以内;致渍型降水3.8次/年,3~9月份均有可能发生,其中5、6月发生频率最高(80%左右);致涝型降水主要出现在6~8月份,出现的频率分别为32.1%、37.7%和24.5%;致渍型降水出现的频次远大于致涝型降水,二者之比为2.63∶1;导致农田涝渍相随现象的降水有明显的季节性和一定重现期,春季约3年一遇,春夏过渡期约4.4年出现一次,夏季约3.5年一遇。     

Development of DRAIN-WARMF model to simulate flow and nitrogen transport in a tile-drained agricultural watershed in Eastern Canada

A new watershed model, DRAIN-WARMF, was developed to simulate the hydrologic processes and the nitrogen fate and transport that occur in small, predominantly subsurface-drained, agricultural watersheds that experience periodic freezing and thawing conditions. In this modeling approach, surface flow is simulated using a watershed scale model, WARMF, and subsurface flow is estimated using a field-scale model for subsurface-drained shallow water table fields, DRAINMOD 5.1. For subsurface flow calculations, the watershed is subdivided into uniform cells, and DRAINMOD is run on each cell with inputs based on the individual hydrologic characteristics of the cell. The coupling results in a distributed parameter model that calculates the total flow at the outlet of a watershed as well as the nitrogen losses. The model was evaluated for the St. Esprit watershed, located approximately 50 km northeast of Montreal. Simulations were carried out from 1994 to 1996; data from 1994 and 1995 was used for model calibration and data from 1996 was used for model validation. The new model was able to adequately simulate the hydrologic response and nitrate losses at the outlet of the watershed. Comparing the observed daily flow/monthly nitrogen with the model's outputs over the validation period returned an R² value of 0.74/0.86 and modeling efficiency of 0.72/0.83. This clearly demonstrates the model's ability to simulate hydrology and nitrogen losses occurring in small agricultural watersheds in cold climates.     

岩溶流域典型农业区水体氢氧同位素的空间异质性及形成机制

分别于平水期和枯水期采集了花溪河流域典型农业区地表水和地下水样品。利用氢氧同位素示踪技术,结合土地利用类型对研究区不同水体的补给来源、季节变化及主要影响过程进行了分析,并对不同水体氢氧同位素值进行了空间插值分析,同时对其形成机制进行了分析,阐明了不同土地利用类型影响下的主要水文过程。结果表明:(1)研究区不同水体的主要补给来源为当地大气降水,月亮湖水库受蒸发作用影响明显,地表水和地下水的δD和δ~(18)O整体上呈现平水期高于枯水期的特征。(2)地下水的δD和δ~(18)O在枯水期与平水期均呈现明显的空间分异性特征,西部水田/水库集中区富集,东部旱地集中区贫化,土地利用对研究区环境水文过程影响明显。该研究结果有助于了解不同土地利用方式下地表水对地下水的影响,为流域管理提供科学依据。     

Estimating episodic recharge under different crop/pasture rotations in the Mallee region. Part 2. Recharge control by agronomic practices

Much environmental degradation, including salinity in the Mallee region of southeastern Australia, is associated with the loss of native vegetation and increased recharge. As a result, various agronomic practices have been proposed to reduce groundwater recharge. This study was conducted to evaluate the impact of these practices on recharge, in particular episodic recharge. A biophysically based model (WAVES) was used to estimate recharge rates under some typical crop and pasture rotations in the region using long-term meteorological data. Results show that: (1) recharge just below the root zone was episodic and that just 10% of annual recharge events contributed over 85% of long-term totals. Management options such as incorporating lucerne and deep-rooted non-fallow rotations can reduce both, mean annual recharge, and the number of episodic events, but not eliminate recharge completely; (2) winter fallows increased soil-water storage and some of the additional water was stored in the lower portion of the root zone or below it. This can increase the risk of recharge to groundwater system; (3) changes in land management may take a considerable period of time (>10 years) to have any noticeable impacts on recharge; and (4) recharge under lucerne was ≈30% of that under medic pasture.     

数值模型结构不确定性对模拟结果的影响分析

以内蒙古鄂托克旗为例,基于GMS中的MODFLOW模块构建了地下水流数值模拟模型,分析了模型结构(含水层厚度、参数分区)与模型参数不确定性因素对模拟结果的影响.研究结果表明:含水层不确定情景(含水层下边界概化为隔水底板平均值870 m)与实际情况水头差值绝对值的累计和最大为701 m,对模拟结果起了主控作用;当含水层下边界概化为910,940 m时,累计和分别增加为1 013,1 593 m;与仅考虑单个不确定性因素相比,同时考虑模型参数与含水层不确定情景累计和最大为738 m,同时考虑参数分区与含水层不确定情景累计和最大为791 m.因此,在构建地下水流数值模拟模型时,应优先考虑含水层空间结构概化的合理程度,同时考虑多个不确定性因素对模拟结果的综合影响,使地下水数值模拟模型能更精确地反映真实的地下水流状况.     

河套灌区井渠结合地下水数值模拟及均衡分析

建立了河套灌区三维地下水数值模型,用2006-2013年灌区实测地下水埋深资料对模型进行率定和验证,并在规划的井渠结合区内,设置3种不同井灌区灌溉定额和3种秋浇频率,组合共9种井渠结合节水情景,分别分析了9种节水情景下的地下水动态变化.结果表明:井渠结合后全灌区地下水埋深范围为1.863~2.029 m,较现状条件增加0.084~0.250 m;不同灌域结合区井渠结合后地下水埋深差别很大,解放闸结合区地下水埋深最大,为2.308~2.803 m,永济结合区地下水埋深最小,为2.079~2.455 m;井渠结合后,入渗补给量减少2.01×10⁸ ~3.63×10⁸ m³/a,潜水蒸发量减少1.69×10⁸ ~3.03×10⁸ m³/a.     

基于地下水均衡的灌区合理渠井用水比例

基于地下水均衡模型,分析了陕西泾惠渠灌区不同频率典型年的地下水均衡状况,结果表明降水入渗补给、渠系渗漏及田间灌溉入渗补给、井灌回归补给是灌区地下水的主要补给源,占总补给量的85.99%~82.89%;而人工开采是灌区地下水的主要排泄途径,农灌地下水开采量、人畜和工业用水开采量占总排泄量的69.7%~72.86%.以2010年为现状基准年,2020年为规划水平年,结合灌区发展规划,设置了4种不同的灌区发展情景模式,运用所建立的地下水均衡模型计算了不同情景模式下的地下水位埋深,其变化范围为0~0.07 m;以地下水位变幅最小为准则,得出了不同频率典型年合理的渠井用水比例范围为1.49~1.53,从而为灌区地下水资源的高效持续利用提供了依据.