Integrated Surface–Subsurface Modeling of Fuxianhu Lake Catchment, Southwest China

This paper describes an integrated surface–subsurface modeling study of the Fuxianhu Lake catchment (southwest China). Pollution threats to this important water resource have led to the need to evaluate transport pathways and the overall water balance of the catchment. Catchment inputs to the lake include river inflows, direct overland flow and groundwater discharge, which are incorporated into a mathematical model of the system. Surface runoff and groundwater recharge are estimated using a parsimonious soil–vegetation modeling approach, while groundwater flow is based on the MODFLOW-2005 code. Overland flow and stream discharge are coupled to the groundwater regime through the soil layer and are routed through the catchment to account for surface water flow pathways. The model is tested using the V-catchment benchmark problem and is compared to existing models to demonstrate accuracy and capability. Application of the model to the Fuxianhu catchment provides for the first-order approximation of the average catchment water balance, which comprises such components as evapotranspiration losses (37% of rainfall), surface runoff to the lake (37% of rainfall), and groundwater discharge to the lake (8% of rainfall), amongst others. The computationally efficient approach to surface–subsurface modeling adopted in this investigation presents as an alternative to more complex methods, and allows for the rapid assessment of flow pathways at the catchment scale. An erratum to this article can be found at     

Hydrological behaviour and water balance analysis for Xitiaoxi catchment of Taihu Basin

With the rapid social and economic development of the Taihu region, Taihu Lake now faces an increasingly severe eutrophication problem. Pollution from surrounding catchments contributes greatly to the eutrophication of water bodies in the region. Investigation of surface flow and associated mass transport for the Xitiaoxi catchment is of a significant degree of importance as the Xitiaoxi catchment is one of the major catchments within the Taihu region. A SWAT-based distributed hydrological model was established for the Xitiaoxi catchment. The model was calibrated and verified using hydrometeorological data from 1988 to 2001. The results indicate that the modeled daily and annual stream flow match the observed data both in the calibration period and the verification period, with a linear regression coefficient R2 and a coefficient e for modeled daily stream flow greater than 0.8 at Hengtangcun and Fanjiacun gauge stations. The results show that the runoff process in the Xitiaoxi catchment is affected both by rainfall and human activities （e.g., reservoirs and polder areas）. Moreover, the human activities weaken flood peaks more noticeably during rainstorms. The Water balance analysis reveals the percentages of precipitation made up by surface flow, evapotranspiration, groundwater recharge＇ and the change of soil storage, all of which are considered useful to the further understanding of the hydrological processes in the Xitiaoxi catchment. This study provides a good base for further studies in mass transport modeling and comparison of modeling results from similar hydrological models.     

Modelling Impacts of Land Cover Change on Critical Water Resources in the Motueka River Catchment, New Zealand

After the SWAT (Soil and Water Assessment Tool) model was calibrated and validated to historic flow records for the current land use conditions, two additional land cover scenarios (a prehistoric land cover and a potential maximum plantation pine cover) were used to evaluate the impacts of land cover change on total water yields, groundwater flow, and quick flow in the Motueka River catchment, New Zealand. Low-flow characteristics and their potential impacts on availability for water abstraction and for support of in-stream habitat values were focused on. The results showed that the annual total water yields, quick flow and baseflow decreased moderately in the two scenarios when compared with the current actual land use. The annual water balance for the pine potential land cover scenario did not differ substantially from the prehistoric scenario for the catchment as whole. However, there were more notable differences among individual tributary catchments, which could be attributed to the relative area of land cover altered and location of those catchments. Simulated low flows for the prehistoric and potential pine land cover scenarios were both significantly lower than the low flows for the current land use. In summary, under the current land use conditions, both annual water yield and low flow are higher than was the case before human intervention in the area or in a maximum commercial reforestation scenario.     

River regulation by seasonal groundwater abstraction: The case of the River Itchen

This paper describes the development of groundwater to regulate the flows of the River Itchen in Southern England. The permeable chalk geology of the river catchment makes the use of natural groundwater storage more cost effective than conventional surface reservoirs. The principles of groundwater regulation and the construction and testing of the first two schemes are described. Flow extension and mathematical modelling have been used to assess yields and assist with operational decisions. The paper concludes that groundwater regulation is a viable alternative to reservoirs in permeable catchments and further schemes are planned.     

The influence of stream bed hydraulic conductivity on sustaining baseflow in rivers.

This study presents the results of the influence of stream bed hydraulic conductivity on baseflow sustainability by using a coupled model of surface and subsurface hydrology. The model provides a coupled solution to the dynamic interactions between a river and a surfacial aquifer and is used to numerically study the effect of stream bed conductivity on the overall system response. To achieve this objective, the model is formulated to include a one-dimensional river flow model and a two-dimensional vertically averaged groundwater flow model in an unconfined aquifer. The coupling is achieved at the river bed via a hydraulic flux that is described as a function of river bed conductivity and the gradient between river stage and groundwater head. The model incorporates the concept of simultaneous presence of the two hydrologic processes for simulating the dynamic interactions and uses a novel numerical technique to solve the two systems concurrently. These interactions are analyzed by numerical experimentation under different hydraulic conductivity conditions. The influence of hydraulic conductivity and hydraulic gradient is studied under steady and unsteady flow regimes to assess the occurrence of baseflow. The analysis also reveals critical insights into the governing mechanisms that provide and sustain the baseflow in rivers.     

Contribution of bunker silo effluent discharged via a riparian zone to watershed phosphorus loads

Nutrient losses from agricultural operations are a major contributor to the eutrophication of freshwaters. Although many studies have quantified diffuse nutrient losses, less is known about agricultural point-source contributions, such as bunker silos, to watershed phosphorus (P) loads. This study examined the contributions of a dairy farm bunker silo effluent to watershed soluble reactive P (SRP) and total P (TP) losses. The bunker silo effluent discharged to an adjacent stream via a riparian soakaway for ca. 15 years. Prior to the annual refilling of the bunker silo, flow weighted mean concentrations of SRP (TP) were similar between stream locations up and downstream of the farm. After the bunker silo was refilled, flow-weighted SRP (TP) concentrations in the stream increased by factors of 1.5(2.2) during events and 3.1(2.3) during baseflow. Higher P concentrations occurred in the riparian soils receiving bunker silo effluent (525–3125 mg/kg TP, and 0.1–9.9 mg/kg water extractable P (WEP), compared with 525–939 mg/kg TP, and 0.11–1.43 mg/kg WEP on the opposite side of the stream with no bunker silo effluent. Riparian soils impacted by the bunker silo were near P-saturation, and the riparian zone did little to reduce P transfer in shallow groundwater. The net contributions of bunker silo effluent to annual watershed P losses were 32% (SRP) and 22% (TP). This study highlights the importance of agricultural point sources, and the need to quantify their contributions to watershed P budgets to target P remediation effectively.     

Application of Monte Carlo Simulation Technique to Design Flood Estimation: A Case Study for North Johnstone River in Queensland, Australia

The traditional rainfall-runoff modelling based on the Design Event Approach has some serious limitations as this ignores the probabilistic nature of the key flood producing variables in the modelling except for rainfall depth. A more holistic approach of design flood estimation such as the Joint Probability Approach/Monte Carlo simulation can overcome some of the limitations associated with the Design Event Approach. The Monte Carlo simulation technique is based on the principle that flood producing variables are random variables instead of fixed values. This allows accounting for the inherent variability in the flood producing variables in the rainfall-runoff modelling. This paper applies the Monte Carlo simulation technique and hydrologic model URBS to a large catchment with multiple pluviograph and stream gauging stations. It has been found that it is quite feasible to apply the Monte Carlo simulation technique to large catchments. The Monte Carlo simulation technique has much greater flexibility than the Design Event approach and can provide more realistic design flood estimates with multiple scenarios, which is likely to replace the Design Event Approach. The method developed here can be applied to other catchments in Australia and other countries.     

A coupled model simulation assessment of shallow water-table rise in a Saudi Arabian coastal city

The problem of a rising shallow water-table level in the coastal city of Dammam in eastern Saudi Arabia was investigated through data collection, analysis, and numerical modelling. The research focused on applying a coupled model that considers flow in both the saturated and unsaturated zones. Geophysical and hydrogeological data were collected through field investigations, and various analyses of this data were performed. A computer simulation model of shallow groundwater flow was developed and applied to define the recharge sources. The generalised HYDRUS and MODFLOW modelling packages were coupled to simulate the vadose zone and saturated zone, respectively. The calibrated coupled groundwater model was used to determine the contributions of each possible recharge source, and thus to identify the major causes of the rise in the water table. The shallow water-table rise was found to be a serious threat to the present and future development of this large city.     

Catchment Storage and its Influence on Summer Low Flows in Central European Mountainous Catchments

The objective of this study was to determine the role of spring catchment water storage on the evolution of low flows in central European mountainous catchments. The study analysed 58 catchments for which catchment storage, represented by snow, soil water and groundwater storages, was determined by the HBV hydrological model over a 35-year period. The spring catchment storage was related to several streamflow indices describing low flow periods using the mutual information criterion. The mean runoff in the summer and autumn periods was mostly related to rainfall sums from the respective season. The median relative contribution of rainfall to the total mutual information value was 48.4% in summer, and 44.2% in autumn period, respectively. The relative contribution of soil water and groundwater storages was approximately 25% for each of the components. In contrast, the minimum runoff, its duration and deficit runoff volume, were equally related to both catchment storage and seasonal rainfall, especially in the autumn period.

     

Hydrogeochemistry,Isotopic Composition and Water Age in the Hydrologic System of a Large Catchment within a Plain Humid Environment (Argentine Pampas): Quequén Grande River,Argentina

The Quequén Grande River (QGR) is a large catchment (10 000 km²) in the Pampa Plain in Argentina. From November 2004 to April 2013, a hydrochemical and stable isotopes monitoring program was conducted, which included three sampling stations of monthly composite precipitation, weekly samples in two sites along the river and several groundwater samples. A standard data interpretation was initially performed applying standard statistics, Piper diagrams and δ¹⁸O versus δ²H diagrams. The time evolution of the values of δ¹⁸O in precipitation and streamwater were also determined. The integration of hydrogeochemistry and stable isotopes data indicates the existence of three main components of streamflow: (i) baseflow characterized by electrical conductivity (EC) from 1200 to 1800 µs/cm and an isotope composition quite constant around δ¹⁸O ?5.3‰ and δ²H ?33.8‰. Water age for groundwater contribution is typically around 30 to 40 years using chlorofluorocarbons; (ii) direct runoff composed of channel interception and overland flow, which is of low EC in the order of 50 to 100 µs/cm, and a highly variable isotopic composition; and (iii) translatory flow (pre‐event water that is stored within the subsoil) with an intermediate EC and isotopic composition close to that of the weighted average composition of precipitation. The hydrochemical and stable isotopic data allow the differentiation between baseflow and direct runoff. In addition to this, chlorofluorocarbon dating is a useful tool in assessing the dominance of baseflow in a stream. The data lead to a conceptual model in which an intermediate flow system, with mean residence time (MRT) of around 35 years, discharges into the drainage network. A regional flow system (MRT > 50 years) discharges to the ocean. It is concluded that in this large plain catchment streamflow separation, only two components can be applied in: (i) short storm precipitation events having a high sampling frequency and (ii) during long dry periods when pre‐event soil water is not released. Copyright © 2016 John Wiley & Sons, Ltd.     

基于数字滤波法的怒江流域基流时空分异

为明晰怒江流域基流时空分异特征,利用数字滤波法进行怒江干流和南汀河支流的基流研究。结果表明:1怒江干流3站基流指数IBF在0.71~0.74之间,南汀河支流2站的多年平均IBF在0.68左右,南汀河支流IBF明显低于怒江干流,干支流基流量和IBF自上游向下游递增;2各站基流量与径流量变化过程基本一致,两者相关系数均在0.9以上;3怒江干支流各站多年平均基流量和径流量年内分配均呈"尖廋"的单峰形,而多年平均基流指数年内分配均呈"V"字形,但两者变化过程不完全相反;4怒江干流代表站道街坝站和南汀河支流代表站姑老河站IBF均为丰水年平水年枯水年,这与基流相对于径流更为稳定有关。     

POTENTIAL FOR VEGETATION‐BASED RIVER MANAGEMENT IN DRYLAND,SALINE CATCHMENTS

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation‐based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation‐based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation‐based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1‐D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20 000–93 000 mg L^?1), there is still a strong potential for successful vegetation‐based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation‐based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high‐value infrastructure and biodiversity assets. Copyright © 2011 John Wiley & Sons, Ltd.     

Developing interdisciplinary science for integrated catchment management: the UK lowland catchment research (LOCAR) programme

Across the European Union, the Water Framework Directive is a major driver for change in river basin management. However, its focus on integrated management and, in particular, on ecological quality raises major scientific and technical questions. In the UK, the focus of experimental hydrology has been on the uplands, and at small catchment scale (< 10 km²), whereas major management pressures lie in the lowlands, and for catchment management units of about 300–400 km². Particular problems arise for permeable lowland catchments: the scientific understanding of the major UK aquifers (the Chalk and the Triassic Sandstone) is poor, and tools for the integrated modelling of surface water–groundwater interactions are limited. In response to these factors, the LOwland CAtchment Research programme (LOCAR) was conceived. A major objective of the programme is to develop new interdisciplinary science and improved modelling tools to meet the challenges of integrated catchment management. The paper describes the research programme and addresses the issues raised in designing and implementing a major interdisciplinary research initiative.     

A Framework for Dry Period Low Flow Forecasting in Mediterranean Streams

The objective of this article is to provide a simple and effective tool for low flow forecasting up to six months ahead, with minimal data requirements, i.e. flow observations retrieved at the end of wet period (first half of April, for the Mediterranean region). The core of the methodological framework is the exponential decay function, while the typical split-sample approach for model calibration, which is known to suffer from the dependence on the selection of the calibration data set, is enhanced by introducing the so-called Randomly Selected Multiple Subsets (RSMS) calibration procedure. Moreover, we introduce and employ a modified efficiency metric, since in this modelling context the classical Nash-Sutcliffe efficiency yields unrealistically high performance. The proposed framework is evaluated at 25 Mediterranean rivers of different scales and flow dynamics, including streams with intermittent regime. Initially, signal processing and data smoothing techniques are applied to the raw hydrograph, in order to cut-off high flows that are due to flood events occurring in dry periods, and allow for keeping the decaying form of the baseflow component. We then employ the linear reservoir model to extract the annually varying recession coefficient, and, then, attempt to explain its median value (over a number of years) on the basis of typical hydrological indices and the catchment area. Next, we run the model in forecasting mode, by considering that the recession coefficient of each dry period ahead is a linear function of the observed flow at the end of the wet period. In most of the examined catchments, the model exhibits very satisfactory predictive capacity and is also robust, as indicated by the limited variability of the optimized model parameters across randomly selected calibration sets.     

Identifying and alleviating low flows in regulated rivers: the case of the Rivers Bulbourne and Gade,Hertfordshire, UK

This paper examines evidence for the occurrence and causes of low flows, and strategies for their mitigation, in two regulated, chalk‐fed streams. The rivers occupy adjacent catchments of similar topography, have long histories of water exploitation and land‐use change, and are subject to conflicting demands of water resource development and increased pressure for environmental improvement. In one case, a strategy of low‐flow mitigation based upon reduced groundwater abstraction has been proposed. Although flows are shown to be declining through time, and low flows are more common over the last decade, analysis of rainfall records and groundwater levels produce inconclusive evidence for the causes of low flows. Despite their natural similarities, the catchments are shown to have very different sensitivities to low flow. When concentrating upon quantity of low flow, the River Gade appears to be most compromised, but when consideration is taken of water quality, the Bulbourne is more severely affected. An examination of catchment changes over a longer time period provides the best rationale for these sensitivities and contrasts. The study illustrates the potential danger of starting with a solely climatic–hydrological perspective to low flows which then progresses to a hydrological ‘solution’. Consideration of catchment land‐use history, and of the importance of water quality, suggest limited applicability of reduced abstraction in mitigating low‐flow problems in these kinds of environments. The study reinforces calls for further studies of groundwater–surface water interaction as essential inputs to appropriate and sustainable water resource management strategies. Copyright © 2000 John Wiley & Sons, Ltd.     

Urbanisation and Shallow Groundwater: Predicting Changes in Catchment Hydrological Responses

The impact of urbanisation on catchment hydrological response was investigated by using a process-based coupled surface water–groundwater model (MODHMS). The modelling estimated likely changes in river discharge as a result of land-use change in the Southern River catchment in Western Australia, underlined by a highly transmissive aquifer, has permeable soils and a shallow watertable. A significant increase in total annual discharge was predicted as a result of urbanisation area with the runoff coefficient rising from 0.01 to more than 0.40. In contrast with urban areas elsewhere, these changes were mainly due to a shift in the subsurface water balance, leading to significant reduction in evaporative losses from the soil profile and shallow watertable after urbanisation (from nearly 80 % of infiltration to less than 20 %). The infiltration of roof and road runoff and establishment of subsurface drainage adopted in local construction practice leads to higher groundwater recharge rates and subsequently groundwater discharge to the urban drainage network. Urban density and groundwater abstraction for urban irrigation most strongly influence the urbanisation impact on catchment fluxes. The results shows that urban development leads to a production of ‘harvestable’ water; and depending on local needs, this water could be used for public and private water supply or to improve environmental flows.     

Modeling of Surface Runoff in Xitiaoxi Catchment,China

Xitiaoxi catchment is one of the most important catchments in the Taihu basin in China. Due to its significant contribution of surface runoff and associated nutrients input to Lake Taihu, understanding of the processes of surface runoff in this catchment is, therefore, of primary importance in quantifying water and nutrient balances for Lake Taihu. The generation of surface runoff in the catchment is mainly controlled by rainfall and land cover, so the variety of surface runoff in Xitiaoxi catchment is seasonal. Moreover, the annual change of surface runoff is distinct. Because of the diversity of land use and variety of hydrological characteristics, numerical simulation of the generation of surface runoff over this catchment is not straightforward. In this paper, attempts were made in applying the Large Scale Catchment Model (LASCAM) to Xitiaoxi catchment. The Xitiaoxi catchment is divided into 47 subcatchments connected via a river network based on topology. The model was first run in an optimization mode to calibrate the parameters against the observed runoff for the period of 1968–1977, and then was run in a prediction mode to try to reproduce the runoff for the next 10 years from 1978 to 1987. The model indicates that saturation excess runoff is probably the dominant process for the catchment. The modeling results indicate that water storage in shallow soils near the stream has a high correlation with daily rainfall, while the water storage changes in deep aquifers demonstrate an annual change trend, showing a rising level for wet seasons and a declining level for dry seasons. The success in modeling surface runoff leads to confidence in modeling nutrients transport as the next step of modeling work.     

Groundwater recharge in an endoreic basin with reclaimed municipal wastewater.

The aim of this paper was to evaluate the groundwater pollution in an endoreic basin in southern Italy. The aquifer circulation was carried out on two different levels: a shallow groundwater, with a water table of about 10 m, and a deep groundwater in a karst aquifer, with a water table of 140-190 m. Reclaimed municipal wastewater and superficial water collected in the catchment area were both drained in a swallow hole linked with the deep groundwater. The agricultural practice conducted in the endoreic basin produced an excess of nitrate in the soil. Nitrate was subsequently washed out and displaced in the groundwater. With regard to the EU Drinking Water Directive (98/83/EC), the research activity conducted during 2003 showed the absence of pollution in the deep groundwater used for drinking water supply. The shallow groundwater, instead, was strongly influenced by agricultural and pasture activities, with detectable levels of nitrates and bacteria. In order to reduce the load of pollution entering the swallow hole and then in the deep groundwater, the realisation of a constructed wetland plant was proposed to improve the quality of reclaimed wastewater, as well as to pursue the wastewater reuse in agriculture.     

Application of Water Balance Models to Different Climatic Regions in China for Water Resources Assessment

Uneven precipitation in space and time together with mismanagement and lack of knowledge about existing water resources, have caused water shortage problems for water supply to large cities and irrigation in many regions of China. There is an urgent need for the efficient use and regional planning of water resources. For these purposes, the monthly variation of discharges should be made available. In this paper, a simple water balance modelling approach was applied to seven catchments (385–2000²) for water resources assessment. Six catchments were chosen from the humid region in southern China and one catchment from the semi-arid and semi-humid region in northern China. The results are satisfactory. It is suggested that the proposed modelling approach provides a valuable tool in the hands of planners and designers of water resources.