Modelling the effects of land‐use change on water and salt delivery from a catchment affected by dryland salinity in south‐east Australia

A comprehensive framework for the assessment of water and salt balance for large catchments affected by dryland salinity is applied to the Boorowa River catchment (1550 km²), located in south‐eastern Australia. The framework comprised two models, each focusing on a different aspect and operating on a different scale. A quasi‐physical semi‐distributed model CATSALT was used to estimate runoff and salt fluxes from different source areas within the catchment. The effects of land use, climate, topography, soils and geology are included. A groundwater model FLOWTUBE was used to estimate the long‐term effects of land‐use change on groundwater discharge. Unlike conventional salinity studies that focus on groundwater alone, this study makes use of a new approach to explore surface and groundwater interactions with salt stores and the stream. Land‐use change scenarios based on increased perennial pasture and tree‐cover content of the vegetation, aimed at high leakage and saline discharge areas, are investigated. Likely downstream impacts of the reduction in flow and salt export are estimated. The water balance model was able to simulate both the daily observed stream flow and salt load at the catchment outlet for high and low flow conditions satisfactorily. Mean leakage rate of about 23·2 mm year^?1 under current land use for the Boorowa catchment was estimated. The corresponding mean runoff and salt export from the catchment were 89 382 ML year^?1 and 38 938 t year^?1, respectively. Investigation of various land‐use change scenarios indicates that changing annual pastures and cropping areas to perennial pastures is not likely to result in substantial improvement of water quality in the Boorowa River. A land‐use change of about 20% tree‐cover, specifically targeting high recharge and the saline discharge areas, would be needed to decrease stream salinity by 150 µS cm^?1 from its current level. Stream salinity reductions of about 20 µS cm^?1 in the main Lachlan River downstream of the confluence of the Boorowa River is predicted. The FLOWTUBE modelling within the Boorowa River catchment indicated that discharge areas under increased recharge conditions could re‐equilibrate in around 20 years for the catchment, and around 15 years for individual hillslopes. Copyright © 2004 John Wiley & Sons, Ltd.     

Groundwater monitoring at the watershed scale: An evaluation of recharge and nonpoint source pollutant loading in the Clear Creek Watershed,Iowa

Determining the groundwater contribution of nonpoint source pollution at a watershed scale is a challenging issue. In this study, we utilized a top‐down approach to characterize representative groundwater response units (GRUs) based on land use and landscape position (e.g., upland, sideslope, or floodplain) in the 275‐km² Clear Creek Watershed, Iowa. Groundwater monitoring wells were then established along downslope transects in representative GRUs. This unique combination of top‐down/bottom‐up approaches allowed us to estimate groundwater pollutant loads at the watershed scale with minimal monitoring. For the 2015 study period, results indicated that more groundwater recharge occurred in the floodplain (404 mm) compared to the uplands or sideslopes (281 and 165 mm, respectively), irrespective of land use. Recharge in the floodplains consisted of 37% of the annual precipitation, whereas upland wells averaged 26% and sideslopes averaged 15% of the annual precipitation. Less recharge was found to occur beneath perennial grass compared to row crop and urbanized areas. Baseflow discharge accounted for 69% of the total NO₃‐N exported from the Clear Creek Watershed, with row crop areas contributing approximately 95% of the annual load. Orthophosphorus (OP) yields were approximately 0.72 kg/ha beneath urban and suburban areas, three times higher than those in row crop or perennial areas. Urban and suburban areas accounted for 21.4% of groundwater orthophosphorus and chloride loads in the watershed compared to only 8.5% of the land area. Overall, the groundwater load allocation model for baseflow nutrient discharge to Clear Creek can be used to target future nonpoint source load reduction strategies at the watershed scale. The use of GRUs can pinpoint better areas of concern for controlling nutrient loads.     

The Role of Groundwater for Lake‐Water Quality and Quantification of N Seepage

The heterogeneous nature of both groundwater discharge to a lake (inflow) and nitrate concentrations in groundwater can lead to significant errors in calculations of nutrient loading. Therefore, an integrated approach, combining groundwater flow and transport modelling with observed nitrate and ammonium groundwater concentrations, was used to estimate nitrate loading from a catchment via groundwater to an oligotrophic flow‐through lake (Lake Hampen, Denmark). The transport model was calibrated against three vertical nitrate profiles from multi‐level wells and 17 shallow wells bordering a crop field near the lake. Nitrate concentrations in groundwater discharging to the lake from the crop field were on average 70 times higher than in groundwater from forested areas. The crop field was responsible for 96% of the total nitrate loading (16.2 t NO₃/year) to the lake even though the field only covered 4.5% of the catchment area. Consequently, a small change in land use in the catchment will have a large effect on the lake nutrient balance and possible lake restoration. The study is the first known attempt to estimate the decrease of nitrate loading via groundwater to a seepage lake when an identified catchment source (a crop field) is removed.     

Recharge estimation using remotely sensed evapotranspiration in an irrigated catchment in southeast Australia

Reliable estimates of groundwater recharge are required for the sustainable management of surface and ground water resources in semi‐arid regions particularly in irrigated regions. In this study, groundwater recharge was estimated for an irrigated catchment in southeast Australia using a semi‐distributed hydrological model (SWAT). The model was calibrated under the dry climatic conditions for the period from August 2002 to July 2003 using flow and remotely sensed evapotranspiration (ET). The model was able to simulate observed monthly drain flow and spatially distributed remotely sensed ET. Recharge tended to be higher for irrigated land covers, such as perennial pasture, than for non‐irrigated land. On average, the estimated annual catchment recharge ranged between 147 and 289 mm which represented about 40% of the total rainfall and irrigation inputs. The optimized soil parameters indirectly reflected flow bypassing the soil matrix that could be responsible for this substantial amount of recharge. Overall, the estimated recharge was much more than that previously estimated for the wetter years. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales

Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd.     

Modelling the potential impacts of groundwater hydrology on long‐term drainage basin evolution

Fluvial erosion processes are driven by water discharge on the land surface, which is produced by surface runoff and groundwater discharge. Although groundwater is often neglected in long‐term landscape evolution problems, water table levels control patterns of Dunne runoff production, and groundwater discharge can contribute significantly to storm flows. In this analysis, we investigate the role that groundwater movement plays in long‐term drainage basin evolution by modifying a widely used landscape evolution model to include a more detailed representation of basin hydrology. Precipitation is generated by a stochastic process, and the precipitation is partitioned between surface runoff and groundwater recharge using a specified infiltration capacity. Groundwater flow is simulated by a dynamic two‐dimensional Dupuit equation for an unconfined aquifer with an irregular underlying impervious layer. The model is applied to the WE‐38 basin, an experimental catchment in Pennsylvania, because 60–80 per cent of the discharge is derived from groundwater and substantial hydrologic and geomorphic information is available. The hydrologic model is first calibrated to match the observed streamflows, and then the combined hydrologic/geomorphic model is used to simulate scenarios with different infiltration capacities. The results of this modelling exercise indicate that the basin can be divided into three zones with distinct streamflow‐generating characteristics, and different parts of the basin can have different geomorphic effective events. Over long periods of time, scenarios in which groundwater discharge is large tend to modify the topography in a way that promotes groundwater discharge and inhibits Dunne runoff. Copyright © 2006 John Wiley & Sons, Ltd.     

Predicting Aquifer Response Time for Application in Catchment Modeling

It is well established that changes in catchment land use can lead to significant impacts on water resources. Where land‐use changes increase evapotranspiration there is a resultant decrease in groundwater recharge, which in turn decreases groundwater discharge to streams. The response time of changes in groundwater discharge to a change in recharge is a key aspect of predicting impacts of land‐use change on catchment water yield. Predicting these impacts across the large catchments relevant to water resource planning can require the estimation of groundwater response times from hundreds of aquifers. At this scale, detailed site‐specific measured data are often absent, and available spatial data are limited. While numerical models can be applied, there is little advantage if there are no detailed data to parameterize them. Simple analytical methods are useful in this situation, as they allow the variability in groundwater response to be incorporated into catchment hydrological models, with minimal modeling overhead. This paper describes an analytical model which has been developed to capture some of the features of real, sloping aquifer systems. The derived groundwater response timescale can be used to parameterize a groundwater discharge function, allowing groundwater response to be predicted in relation to different broad catchment characteristics at a level of complexity which matches the available data. The results from the analytical model are compared to published field data and numerical model results, and provide an approach with broad application to inform water resource planning in other large, data‐scarce catchments.     

Hydrological response of a Brazilian semi‐arid catchment to different land use and climate change scenarios: a modelling study

Brazilian semi‐arid regions are characterized by water scarcity, vulnerability to desertification, and climate variability. The investigation of hydrological processes in this region is of major interest not only for water planning strategies but also to address the possible impact of future climate and land‐use changes on water resources. A hydrological distributed catchment‐scale model (DiCaSM) has been applied to simulate hydrological processes in a small representative catchment of the Brazilian northeast semi‐arid region, and also to investigate the impact of climate and land‐use changes, as well as changes associated with biofuel/energy crops production. The catchment is part of the Brazilian network for semi‐arid hydrology, established by the Brazilian Federal Government. Estimating and modelling streamflow (STF) and recharge in semi‐arid areas is a challenging task, mainly because of limitation in in situ measurements, and also due to the local nature of some processes. Direct recharge measurements are very difficult in semi‐arid catchments and contain a high level of uncertainty. The latter is usually addressed by short‐ and long‐time‐scale calibration and validation at catchment scale, as well as by examining the model sensitivity to the physical parameters responsible for the recharge. The DiCaSM model was run from 2000 to 2008, and streamflow was successfully simulated, with a Nash–Sutcliffe (NS) efficiency coefficient of 0·73, and R² of 0·79. On the basis of a range of climate change scenarios for the region, the DiCaSM model forecasted a reduction by 35%, 68%, and 77%, in groundwater recharge (GWR), and by 34%, 65%, and 72%, in streamflow, for the time spans 2010–2039, 2040–2069, and 2070–2099, respectively, could take place for a dry future climate scenario. These reductions would produce severe impact on water availability in the region. Introducing castor beans to the catchment would increase the GWR and streamflow, mainly if the caatinga areas would be converted into castor beans production. Changing an area of 1000 ha from caatinga to castor beans would increase the GWR by 46% and streamflow by 3%. If the same area of pasture is converted into castor beans, there would be an increase in GWR and streamflow by 24% and 5%, respectively. Such results are expected to contribute towards environmental policies for north‐east Brazil (NEB), and to biofuel production perspectives in the region. Copyright © 2010 John Wiley & Sons, Ltd.     

Does hillslope trenching enhance groundwater recharge and baseflow in the Peruvian Andes?

As Andean glaciers rapidly retreat due to climate change, the balance of groundwater and glacial meltwater contributions to stream discharge in tropical, proglacial watersheds will change, potentially increasing vulnerability of water resources. The Shullcas River Watershed, near Huancayo, Peru, is fed only partly by the rapidly receding Huaytapallana glaciers (<20% of dry season flow). To potentially increase recharge and therefore increase groundwater derived baseflow, the government and not‐for‐profit organizations have installed trenches along large swaths of hillslope in the Shullcas Watershed. Our study focuses on a nonglacierized subcatchment of the Shullcas River Watershed and has 2 objectives: (a) create a model of the Shullcas groundwater system and assess the controls on stream discharge and (b) investigate the impact of the infiltration trenches on recharge and baseflow. We first collected hydrologic data from the field including a year‐long hydrograph (2015–2016), meteorological data (2011–2016), and infiltration measurements. We use a recharge model to evaluate the impact of trenched hillslopes on infiltration and runoff processes. Finally, we use a 3‐dimensional groundwater model, calibrated to the measured dry season baseflow, to determine the impact of trenching on the catchment. Simulations show that trenched hillslopes receive approximately 3.5% more recharge, relative to precipitation, compared with unaltered hillslopes. The groundwater model indicates that because the groundwater flow system is fast and shallow, incorporating trenched hillslopes (~2% of study subcatchment area) only slightly increases baseflow in the dry season. Furthermore, the location of trenching is an important consideration: Trenching higher in the catchment (further from the river) and in flatter terrain provides more baseflow during the dry season. The results of this study may have important implications for Andean landscape management and water resources.     

Opportunities for manipulating catchment water balance by changing vegetation type on a topographic sequence: a simulation study

This simulation study explores opportunities to reduce catchment deep drainage through better matching land use with soil and topography, including the ‘harvesting’ (evapotranspiration) of excess water running on to lower land units. A farming system simulator was coupled with a catchment hydrological framework to enable analysis of climate variability and 11 different land‐use options as they impact the catchment water balance. These land‐use options were arranged in different configurations down a sequence of three hydrologically interconnected slope units (uphill, mid‐slope and valley floor land units) in a subcatchment of Simmons Creek, southern New South Wales, Australia. With annual crops, the valley floor land units were predicted to receive 187 mm year^?1 of run‐on water in addition to annual rainfall in 1 in 10 years, and in excess of 94 mm year^?1 in 1 in 4 years. In this valley floor position, predicted drainage averaged approximately 110 mm year^?1 under annual crops and pastures, whereas permanent tree cover or perennial lucerne was predicted to reduce drainage by up to 99%. The planting of trees or lucerne on the valley floor units could ‘harvest’ run‐on water, reducing drainage for the whole subcatchment with proportionately small reduction in land areas cropped. Upslope land units, even though often having shallower soil, will not necessarily be the most effective locations to plant perennial vegetation for the purposes of recharge reduction. Water harvesting opportunities are site specific, dependent on the amounts and frequency of flows of water to lower landscape units, the amounts and frequency of deep drainage on the different land units, the relative areas of the different land units, and interactions with land use in the different slope positions. Copyright © 2007 John Wiley & Sons, Ltd.     

Predicting storm runoff from different land‐use classes using a geographical information system‐based distributed model

A method is presented to evaluate the storm runoff contributions from different land‐use class areas within a river basin using the geographical information system‐based hydrological model WetSpa. The modelling is based on division of the catchment into a grid mesh. Each cell has a unique response function independent of the functioning of other cells. Summation of the flow responses from the cells with the same land‐use type results in the storm runoff contribution from these areas. The model was applied on the Steinsel catchment in the Alzette river basin, Grand Duchy of Luxembourg, with 52 months of meteo‐hydrological measurements. The simulation results show that the direct runoff from urban areas is dominant for a flood event compared with runoff from other land‐use areas in this catchment, and this tends to increase for small floods and for the dry‐season floods, whereas the interflow from forested, pasture and agricultural field areas contributes to recession flow. It is demonstrated that the relative contribution from urban areas decreases with flow coefficient, that cropland relative contribution is nearly constant, and that the relative contribution from grassland and woodland increases with flow coefficient with regard to their percentage of land‐use class areas within the study catchment. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimating groundwater recharge for an arid karst system using a combined approach of time‐lapse camera monitoring and water balance modelling

Groundwater is the principal water resource in semi‐arid and arid environments. Therefore, quantitative estimates of its replenishment rate are important for managing groundwater systems. In dry regions, karst outcrops often show enhanced recharge rates compared with other surface and sub‐surface conditions. Areas with exposed karst features like sinkholes or open shafts allow point recharge, even from single rainfall events. Using the example of the As Sulb plateau in Saudi Arabia, this study introduces a cost‐effective and robust method for recharge monitoring and modelling in karst outcrops. The measurement of discharge of a representative small catchment (4.0 · 10⁴ m²) into a sinkhole, and hence the direct recharge into the aquifer, was carried out with a time‐lapse camera. During the monitoring period of two rainy seasons (autumn 2012 to spring 2014), four recharge events were recorded. Afterwards, recharge data as well as proxy data about the drying of the sediment cover are used to set up a conceptual water balance model. The model was run for 17 years (1971 to 1986 and 2012 to 2014). Simulation results show highly variable seasonal recharge–precipitation ratios between 0 and 0.27. In addition to the amount of seasonal precipitation, this ratio is influenced by the interannual distribution of rainfall events. Overall, an average annual groundwater recharge for the doline (sinkhole) catchment on As Sulb plateau of 5.1 mm has estimated for the simulation period. Copyright © 2015 John Wiley & Sons, Ltd.     

Improving runoff prediction using agronomical information in a cropped,loess covered catchment

Predicting runoff hot spots and hot‐moments within a headwater crop‐catchment is of the utmost importance to reduce adverse effects on aquatic ecosystems by adapting land use management to control runoff. Reliable predictions of runoff patterns during a crop growing season remain challenging. This is mainly due to the large spatial and temporal variations of topsoil hydraulic properties controlled by complex interactions between weather, growing vegetation, and cropping operations. This interaction can significantly modify runoff patterns and few process‐based models can integrate this evolution of topsoil properties during a crop growing season at the catchment scale. Therefore, the purpose of this study was to better constrain the event‐based hydrological model Limburg Soil Erosion Model by incorporating temporal constraints for input topsoil properties during a crop growing season (LISEM). The results of the temporal constraint strategy (TCS) were compared with a classical event per event calibration strategy (EES) using multi‐scale runoff information (from plot to catchment). The EES and TCS approaches were applied in a loess catchment of 47 ha located 30 km northeast of Strasbourg (Alsace, France). A slight decrease of the Nash–Sutcliffe efficiency criterion on runoff discharge for TCS compared to EES was counterbalanced by a clear improvement of the spatial runoff patterns within the catchment. This study showed that limited agronomical and climatic information added during the calibration step improved the spatial runoff predictions of an event‐based model. Reliable prediction of runoff source, connectivity, and dynamics can then be derived and discussed with stakeholders to identify runoff hot spots and hot‐moments for subsequent land use and crop management modifications.     

Hydrological modelling for assessing spatio-temporal groundwater recharge variations in the water-stressed Amathole Water Supply System,Eastern Cape,South Africa

To increase the resilience of regional water supply systems in South Africa in the face of anticipated climatic changes and a constant increase in water demand, water supply sources require diversification. Many water-stressed metropolitan regions in South Africa depend largely on surface water to cover their water demand. While climatic and river discharge data is widely available in these regions, information on groundwater resources – which could support supply source diversification – is scarce. Groundwater recharge is a key parameter that is used to estimate groundwater amounts that can be sustainably exploited at a sub-watershed level. Therefore, the objective of this study was to develop a reliable hydrological modelling routine that enables the assessment of regional spatio-temporal variations of groundwater recharge to discern the most promising areas for groundwater development. Accordingly, we present a semi-distributed hydrological modelling approach that incorporates water balance routines coupled with baseflow modelling techniques to yield spatio-temporal variations of groundwater recharge on a regional level. The approach is demonstrated for the actively managed catchment areas of the Amathole Water Supply System situated in a semi-arid part of the Eastern Cape of South Africa. In the investigated study area, annual groundwater recharge exhibits a high spatio-temporal heterogeneity and is estimated to vary between ~0.5% and 8% of annual rainfall. Despite some uncertainties induced by limited data availability, calibration and validation of the model were found to be satisfactory and yielded model results similar to (point) data of annual groundwater recharge reported in earlier studies. Our approach is therefore found to derive crucial information for efficiently targeting more detailed groundwater exploration studies and could work as a blueprint for orientating groundwater potential exploration in similar environments.     

Modelling storage‐driven connectivity between landscapes and riverscapes: towards a simple framework for long‐term ecohydrological assessment

The importance of conceptualizing the dynamics of storage‐driven saturation area connectivity in runoff generation has been central to the development of TOPMODEL and similar low parameterized rainfall–runoff models. In this contribution, we show how we developed a 40‐year hydrometric data base to simulate storage–discharge relationships in the Girnock catchment in the Scottish Highlands using a simple conceptual model. The catchment is a unique fisheries reference site where Atlantic salmon populations have been monitored since 1966. The modelling allowed us to track storage dynamics in hillslopes, the riparian zone and groundwater, and explicitly link non‐linear changes of streamflows to landscape storage and connectivity dynamics. This provides a fundamental basis for understanding how the landscape and riverscape are hydrologically connected and how this regulates in‐stream hydraulic conditions that directly influence salmonids. We use the model to simulate storage and discharge dynamics over the 40‐year period of fisheries records. The modelled storage‐driven connectivity provides an ecohydological context for understanding the dynamics in stream flow generation which determine habitat hydraulics for different life stages of salmon population. This new, long‐term modelling now sets this variability in the riverscape in a more fundamental context of the inter‐relationships between storage in the landscape and stream flow generation. This provides a simple, robust framework for future ecohydrological modelling at this site, which is an alternative to more increasingly popular but highly parameterized and uncertain commercial ecohydrological models. It also provides a wider, novel context that is a prerequisite for any model‐based scenario assessment of likely impacts resulting from climate or land use change. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd. Copyright © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.     

Field‐Scale Relationships Among Soil Properties and Shallow Groundwater Quality

It is important to understand the link between land surface/soil properties and shallow groundwater quality. To that end, soil properties and near‐water‐table groundwater chemistry of a shallow, unconfined aquifer were measured on a 100‐m grid on a 64‐ha irrigated field in southeastern North Dakota. Soil properties and hydrochemistry were compared via multivariate analysis that included product‐moment correlations and factor analysis/principal component analysis. Topographic low areas where the water table was in close proximity to the soil surface generally had higher apparent electrical conductivity (EC_a) and higher percent silt and clay than higher positions on the landscape. The majority of the groundwater was characterized by Ca‐ and Mg‐HCO₃ type water and was associated with topographic high areas with lower EC_a and net groundwater recharge. Small topographic depressions were areas of higher EC_a (net groundwater discharge) where salts that precipitated via evapotranspiration and evaporative discharge dissolved and leached to the groundwater during short‐term depression‐focused recharge events. At this site, groundwater quality and soil EC_a were related to surface topography. High‐resolution topography and EC_a measurements are necessary to characterize the land surface/soil properties and surficial groundwater quality at the field‐scale and to delineate areas where the shallow groundwater is most susceptible to contamination.     

Water balance components estimation under scenarios of land cover change in the Vea catchment,West Africa

ABSTRACT

The need for a detailed investigation of the Vea catchment water balance components cannot be overemphasized due to its accelerated land-cover dynamics and the associated impacts on the hydrological processes. This study assessed the possible consequences of land-use change scenarios (i.e. business as usual, BAU, and afforestation for the year 2025) compared to the 2016 baseline on the Vea catchment’s water balance components using the Soil and Water Assessment Tool (SWAT) model. The data used include daily climate and discharge, soil and land use/land cover maps. The results indicate that the mean annual water yield may increase by 9.1% under the BAU scenario but decrease by 2.7% under the afforestation scenario; actual evapotranspiration would decrease under BAU but increase under afforestation; and groundwater recharge may increase under both scenarios but would be more pronounced under the afforestation scenario. These outcomes highlight the significance of land-cover dynamics in water resource management and planning at the catchment.     

Hydrological footprints of urban developments in the Lake Simcoe watershed,Canada: a combined paired‐catchment and change detection modelling approach

Urban sprawl and regional climate variability are major stresses on surface water resources in many places. The Lake Simcoe watershed (LSW) Ontario, Canada, is no exception. The LSW is predominantly agricultural but is experiencing rapid population growth because of its proximity to the Greater Toronto area. This has led to extensive land use changes that have impacted its water resources and altered run‐off patterns in some rivers draining to the lake. Here, we use a paired‐catchment approach, hydrological change detection modelling and remote sensing analysis of satellite images to evaluate the impacts of land use change on the hydrology of the LSW (1994 to 2008). Results show that urbanization increased up to 16% in Lovers Creek, the most urban‐impacted catchment. Annual run‐off from Lovers Creek increased from 239 to 442 mm/year in contrast to the reference catchment (Black River at Washago) where run‐off was relatively stable with an annual mean of 474 mm/year. Increased annual run‐off from Lovers Creek was not accompanied by an increase in annual precipitation. Discriminant function analysis suggests that early (1992–1997; pre‐major development) and late (2004–2009; fully urbanized) periods for Lovers Creek separated mainly based on model parameter sets related to run‐off flashiness and evapotranspiration. As a result, parameterization in either period cannot be used interchangeably to produce credible run‐off simulations in Lovers Creek because of greater scatter between the parameters in canonical space. Separation of early and late‐period parameter sets for the reference catchment was based on climate and snowmelt‐related processes. This suggests that regional climatic variability could be influencing hydrologic change in the reference catchment, whereas urbanization amplified the regional natural hydrologic changes in urbanizing catchments of the LSW. Copyright © 2014 John Wiley & Sons, Ltd.     

A comparison of streamflow,salt and water balances in adjacent farmland and forest catchments in south‐western Victoria,Australia

A study of the hydrologic effects of catchment change from pasture to plantation was carried out in Gatum, south‐western Victoria, Australia. This study describes the hydrologic characteristics of two adjacent catchments: one with 97% grassland and the other one with 62% Eucalyptus globulus plantations. Streamflow from both catchments was intermittent during the 20‐month study period. Monthly streamflow was always greater in the pasture‐dominated catchment compared with the plantation catchment because of lower evapotranspiration in the pasture‐based catchment. This difference in streamflow was also observed even during summer 2010/2011 when precipitation was 74% above average (1954–2012) summer rainfall. Streamflow peaks in the plantation‐based catchment were smaller than in the pasture‐dominated system. Flow duration curves show differences between the pasture and plantation‐dominated catchments and affect both high‐flow and low‐flow periods. Groundwater levels fell (up to 4.4 m) in the plantation catchment during the study period but rose (up to 3.2 m) in the pasture catchment. Higher evapotranspiration in the plantation catchment resulted in falling groundwater levels and greater disconnection of the groundwater system from the stream, resulting in lower baseflow contribution to streamflow. Salt export from each catchment increases with increasing flow and is higher at the pasture catchment, mainly because of the higher flow. Reduced salt loading to streams due to tree planting is generally considered environmentally beneficial in saline areas of south‐eastern Australia, but this benefit is offset by reduced total streamflow. Copyright © 2014 John Wiley & Sons, Ltd.     

Seasonal and interannual behaviour of groundwater catchment boundaries in a Chalk aquifer

Groundwater catchment boundaries and their associated groundwater catchment areas are typically assumed to be fixed on a seasonal basis. We investigated whether this was true for a highly permeable carbonate aquifer in England, the Berkshire and Marlborough Downs Chalk aquifer, using both borehole hydrograph data and a physics‐based distributed regional groundwater model. Borehole hydrograph data time series were used to construct a monthly interpolated water table surface, from which was then derived a monthly groundwater catchment boundary. Results from field data showed that the mean annual variation in groundwater catchment area was about 20% of the mean groundwater catchment area, but interannual variation can be very large, with the largest estimated catchment size being approximately 80% greater than the smallest. The flow in the river was also dependent on the groundwater catchment area. Model results corroborated those based on field data. These findings have significant implications for issues such as definition of source protection zones, recharge estimates based on water balance calculations and integrated conceptual modelling of surface water and groundwater systems. Copyright © 2015 John Wiley & Sons, Ltd.