MIKE SHE Research Articles

Water and salt balance modelling of intermittent catchments using a physically-based integrated model

This paper presents a model of flow and solute transport of intermittent catchments in arid and semi-arid regions, highlighting challenges caused by the complex interactions between subsurface and surface flows. A case study is used for the application of the integrated MIKE SHE model to investigate temporal and spatial dynamics of water and salinity in a small ephemeral catchment in southwestern Victoria, Australia. MIKE SHE was successfully calibrated and validated against experimental data of streamflow, groundwater levels, and salt discharged from the catchment. Projections of climatic conditions, adopting Representative Concentration Pathways (RCPs) 4.5, 6.0, and 8.5, were used to infer how salinity discharge and concentrations might be affected across a range of greenhouse gas emission scenarios with different severity. The calibration of the water fluxes was solely based on parameters associated with the model of evapotranspiration, with other parameters selected from field observations and literature. The calibrated parameters for the salt transport were the longitudinal and lateral dispersivities. The calibration and validation of streamflow series led to Index of Agreement (IoA) of 0.92 and 0.8 respectively, while the simulation of groundwater levels was more challenging (IoA ranging from 0.22 to 0.89). Parameter equifinality was observed, with different parameter sets achieving a good fit of streamflow and groundwater levels, although leading to differing spatial patterns of evapotranspiration rates. Calibration and validation of the discharge concentrations appeared more difficult (IoA of 0.35 for calibration and 0.44 for validation) as they are affected by errors in the simulated flow. Climate projections RCP 8.5 suggested a reduction of salt discharge with consequent increased concentrations within the catchment. The study showed the ability of MIKE SHE to be successfully applied to intermittent dry catchments to possibly support water and land management.

Flow Routing and Surface Water Balance Simulation of a Tank Cascaded Catchment Using Coupled MIKE SHE/MIKE 11 Modeling

Hydrology of a tank cascaded basin in semiarid region is unique and different from a plain terrain hydrology as it consists of intervening surface storage structures called tanks. The incorporation of physical processes of irrigation tank cascaded system in hydrological modeling is essential for accurate estimation and simulation of its water balance components. The earlier studies of rainfall–runoff modeling in such catchments and the effects and processes of these tanks were lumped while modeling as it requires extensive data. Routing through the streams without considering the intervening tank storages will not give accurate estimation of surface water resource potential. Hence, an attempt has been made in this study to characterize the physical processes and to simulate the flow routing through an irrigation tank cascaded system with the application of coupled MIKE SHE and MIKE 11, a fully integrated physically based deterministic and distributed model. With the help of primary and secondary data, the model has been set up by coupling MIKE SHE and MIKE 11 model and the dynamics of water movement has been simulated. The model simulation results have been evaluated through calibration and validation of simulated tank yield with that of observed values. Water level at three tank outlets located at the upper, middle and tail reach of the tank cascaded catchment was used to study the model performance evaluation. The Nash–Sutcliffe coefficients obtained are 0.91, 0.94 and 0.92 for three tank water levels showing satisfactory goodness of fit between the observed and simulated water levels. The statistical parameters obtained from the validation process, such as error matrix, correlation coefficient and Nash–Sutcliffe coefficient values, indicate good simulation and prediction capability of the developed coupled model that incorporates a methodology which takes into account all the physical processes of the tank cascaded system.

Multi-objective calibration of MIKE SHE with SMAP soil moisture datasets

Abstract Root zone soil moisture plays an important role in water storage in hydrological processes. The recently launched Soil Moisture Active Passive (SMAP) mission has produced a high-resolution assimilation product of global root zone soil moisture that can be applied to improve the performance of hydrological models. In this study, we compare three calibration approaches in the Beimiaoji watershed. The first approach is single-objective calibration, in which only observed streamflow is used as a benchmark for comparison with the other approaches. The second and third approaches use multi-objective calibration based on SMAP root zone soil moisture and observed streamflow. The difference between the second and third approaches is the metric used to characterize the root zone soil moisture. The second approach applies the mean, which was commonly used in previous studies, whereas the third approach applies the hydrologic complexity μ, a dimensionless metric based on information entropy theory. These approaches are implemented to calibrate the distributed hydrological model MIKE SHE. Results show that the root zone soil moisture simulation is clearly improved, whereas streamflow simulation suffers from a slightly negative impact with multi-objective calibration. The hydrologic complexity μ performs better than the mean in capturing the features of root zone soil moisture.

Performance evaluation and parameters sensitivity of a distributed hydrological model for a semi-arid catchment in India

In present study, a distributed physics based hydrological model, MIKE SHE coupled with MIKE 11, is calibrated using multi-objective approach, i.e., minimization of error in prediction of stream flows and groundwater levels, using the data of eight years from 1991 to 1998 of Yerli sub-catchment $$(\hbox {area} = 15{,}881\,\hbox {km}^{2})$$ of upper Tapi basin in India. The sensitivity analyses of thirteen model parameters related with overland flow, unsaturated and saturated zones have been undertaken while simulating the runoff volume, peak runoff at catchment outlet and groundwater levels within the catchment with wide variations $$(\pm 50\%)$$ in the model parameters. The calibrated model has also been validated for prediction of stream flow and groundwater levels within the Yerli sub-catchment for period 1999–2004. The simulated results revealed that calibrated model is able to simulate hydrographs satisfactorily for Yerli sub-catchment (NSE $$=$$ 0.65–0.89, $$r=0.80{-}0.95$$ ) at daily and monthly time scales. The ground water levels are predicted reasonably satisfactorily for the plain area (RMSE $$=$$ 0.50–6.50 m) in the study area. The results of total water balance indicated that about 78% of water is lost from the system through evapotranspiration, out of which about 3.5% is contributed from the groundwater zone.

Hydrological assessment of the Teapa River basin, using the MIKE SHE model

En el presente trabajo se ha aplicado el modelo hidrologico MIKE-SHE, para simular procesos de escorrentia de agua de la cuenca hidrologica del rio Teapa, en el sureste de Mexico. La cuenca tiene un clima tropical humedo, altas pendientes y una escasa presencia de nucleos urbanos. Existe informacion detallada sobre las condiciones climaticas, topografia, de vegetacion y suelos de la cuenca, asi como datos del regimen hidrologico del rio Teapa. Se ha implementado el modelo MIKE-SHE, principalmente por la gran capacidad de procesamiento de la informacion detallada de las cuencas. El proceso de simulacion del regimen hidrologico del rio Teapa comprende dos etapas de calculo: la calibracion del modelo, que tiene como finalidad obtener un buen ajuste entre los datos observados y los calculados, lo cual se logra mediante modificacion de algunos de los parametros iniciales relacionados con las propiedades fisicas de los suelos y con la rugosidad hidraulica de la superficie y cauces; la validacion del modelo consiste en la aplicacion del mismo en un periodo sin calibracion y la comparacion de los gastos calculados y observados. Los resultados de la simulacion senalan que en el proceso de validacion del modelo MIKE-SHE se logro un ajuste entre los gastos del rio Teapa medios y maximos mensuales, obteniendo un coeficiente de determinacion R 2 = 0.81. Sin embargo, no se ha logrado buen ajuste de los gastos diarios con R 2 = 0.62

Modelling Groundwater Flow with MIKE SHE Using Conventional Climate Data and Satellite Data as Model Forcing in Haihe Plain, China

In North China Plain, accurate spatial and temporal ET and precipitation pattern is very important in the groundwater resource assessment. This study demonstrated the potential for modelling ET and groundwater processes using remote sensing data for distributed hydrological modelling with MIKE SHE codes in the Haihe Plain, China. The model was successfully validated against independent groundwater level measurements following the calibration period and the model also provided a reasonable match of the lysimeter measurements of ET. The remote sensing data included ET derived from global radiation products of Fengyun-2C geostationary meteorological satellite (FY-2C) and FY-2C precipitation products. The comparisons show that precipitation is a critical factor for the hydrological response and for the spatial distribution of ET and groundwater flow. FY-2C precipitation products has a spatial resolution of about 11 km, which thus adds more spatial variability to the most important driving variable. The ET map based on FY-2C data has a higher spatial variability than that map based on conventional data, which are caused by higher resolution of ground information. The groundwater level changes in the aquifer system are shown in the quite different spatial patterns under two models, which is affected by the significant difference between two types of precipitation. In the Haihe Plain, accurate spatial and temporal ET pattern is very important in the groundwater resource assessment that determines the recharge to the saturated zone.

Seasonal streamflow forecasts in the Ahlergaarde catchment, Denmark: the effect of preprocessing and post-processing on skill and statistical consistency

Abstract. In the present study we analyze the effect of bias adjustments in both meteorological and streamflow forecasts on the skill and statistical consistency of monthly streamflow and yearly minimum daily flow forecasts. Both raw and preprocessed meteorological seasonal forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used as inputs to a spatially distributed, coupled surface–subsurface hydrological model based on the MIKE SHE code. Streamflow predictions are then generated up to 7 months in advance. In addition to this, we post-process streamflow predictions using an empirical quantile mapping technique. Bias, skill and statistical consistency are the qualities evaluated throughout the forecast-generating strategies and we analyze where the different strategies fall short to improve them. ECMWF System 4-based streamflow forecasts tend to show a lower accuracy level than those generated with an ensemble of historical observations, a method commonly known as ensemble streamflow prediction (ESP). This is particularly true at longer lead times, for the dry season and for streamflow stations that exhibit low hydrological model errors. Biases in the mean are better removed by post-processing that in turn is reflected in the higher level of statistical consistency. However, in general, the reduction of these biases is not sufficient to ensure a higher level of accuracy than the ESP forecasts. This is true for both monthly mean and minimum yearly streamflow forecasts. We discuss the importance of including a better estimation of the initial state of the catchment, which may increase the capability of the system to forecast streamflow at longer leads.

High-resolution modelling of the grass swale response to runoff inflows with Mike SHE

The feasibility of simulating the hydrological response of a grass swale to runoff inflows was examined using the hydrological model Mike SHE and the available input data from 12 irrigation events mimicking runoff from block rainfalls. The test swale channel had a trapezoidal cross-section, bottom slope of 1.5%, length of 30 m, and was built in loamy fine sand. The irrigation events consisted in releasing two equal constant inflows to the swale: a concentrated longitudinal flow at the upstream end and a distributed lateral inflow along the swale side slope adjacent to the contributing drainage area. The total inflows approximated runoff from two events with return periods of 2 months and 3 years, respectively, for durations of 30 min. Irrigation experiments were done for two states of the initial soil moisture, dry or wet antecedent moisture conditions (AMC). Mike SHE has been extensively used on catchments of various sizes, but rarely for small stormwater management facilities and their detailed topography investigated in this study. The latter application required high spatial and temporal resolutions, with computational cells of 0.2 × 0.2 m and time steps as short as 0.6 s to avoid computational instabilities. For dominant hydrological processes, the following computational options in Mike SHE were chosen: Soil infiltration – the van Genuchten equation, unsaturated zone flow – the one-dimensional Richards equation, and overland flow – the diffusive wave approximation of the St. Venant equations. For study purposes, the model was calibrated for single events representing one of four combinations of low and high inflows, and dry and wet AMC, and then applied to the remaining 11 events. This was complemented by calibration for two events, representing high inflow on wet AMC and low inflow in dry AMC. The goodness of fit was statistically assessed for observed and simulated peak flows, hydrograph volumes, Nash-Sutcliffe model efficiencies (NSE), and soil water content (SWC) in swale soil layers. The best fit (NSE > 0.8) was obtained for high inflows and wet AMC (i.e., when the primary swale function is flow conveyance); the least fit was noted for low inflows and dry AMC, when the primary swale function is flow attenuation. Furthermore, this observation indicates the overall importance of correct modelling of the soil infiltration. The effects of spatial variation of SWC on the swale discharge hydrograph could not be confirmed from simulation results, but high topographical accuracy was beneficial for reproducing well the locations of the observed water ponding. No significant increases in simulated SWC at 0.3 m or greater depths were noted, which agreed with field observations. Overall, the results indicated that Mike SHE was effective in process-oriented small-scale modelling of grass swale flow hydrographs.

Examining the challenges of simulating surface water–groundwater interactions in a post-glacial environment

Although integrated models are increasingly used for water management purposes, detailed applications of these models under different conditions are necessary to guide their implementation. The objective of this study was to examine some of the challenges encountered when simulating surface water–groundwater interactions in a post-glacial geological environment. The integrated Mike SHE model was used to simulate transient-state heads and flows in the Raquette River watershed in the Vaudreuil-Soulanges region of southwestern Quebec (Canada) over a 2-year period. This application benefited from a detailed hydrogeological database recently developed for the region. Overall, flows, heads and groundwater inputs to the river were adequately simulated. A sensitivity analysis has shown that many hydrogeologic and surface flow parameters have an impact on both flow rates and heads, thus underlining the importance of using an integrated model to study watershed-scale water issues. Additional flow rate measurements to improve the quality of rating curves and continuous flow measurements in tributaries could improve model calibration. An explicit simulation of unsaturated zone infiltration processes, including soil flow, plant and evaporation processes, as well as the inclusion of the agricultural tile drainage system, could reduce simulation errors. Extending the model calibration over a longer period, including contrasting hydrological conditions, would make the model more robust in view of its use for water management under land use and climate change conditions. Nevertheless, this work demonstrated that, using data readily available for southern Québec aquifers, it is possible to build an integrated model that is representative of actual hydrological conditions. The maintenance and improvement of this model for long-term use is recommended.

Combining rainfall–runoff and hydrodynamic models for simulating flow under the impact of climate change to the lower Sai Gon-Dong Nai River basin

This study presented simulation results of runoff discharge combining the Mike NAM and Mike SHE models for lower Sai Gon-Dong Nai River basin (SG-DNRB). Sai Gon-Dong Nai River basin is Vietnam’s largest population center and main industrial area in Ho Chi Minh City. In recent years, the area faces flooding problems because of heavy rainfalls and high tides, as part of the impacts of climate change and sea level rise. The lower of SG-DNRB was selected as a case study to highlight the necessity to investigate combination of the rainfall–runoff model and the hydrodynamic model for long-term strategies to resource water in the future. The models were calibrated using water level and runoff discharge data during low and flood seasons in 2014. The calibrated results showed satisfactory coefficients (NASH index, R2 up to 0.70 and RMSE is smaller than 0.20). The results confirmed that the combination of Mike NAM and Mike SHE models is well suitable to simulate runoff discharge in the lower SG-DNRB. Combination of the models can be considered a useful tool to help professional agency operator water resources management projects in other areas in the context of climate change and sea level rise.

Comparing reach scale hyporheic exchange and denitrification induced by instream restoration structures and natural streambed morphology

Excess nutrients commonly lead to eutrophication and harmful algal blooms. Stream restoration is increasingly popular for nutrient removal enhancing exchange with the reactive hyporheic zone. Hyporheic reactions such as denitrification are often transport-limited and instream restoration structures have been proposed to enhance hyporheic exchange and nutrient removal. However, the comparative effects of instream structure types and watershed setting (i.e. environmental characteristics such as sediment hydraulic conductivity, stream slope) are still poorly understood. Here we used MIKE SHE to model groundwater and surface water interaction and nitrate removal (denitrification) in a 200 m second order stream reach. We simulated various in-stream structures (channel-spanning weirs, partially spanning structures such as cross veins, buried structures) and investigated the effect of controlling environmental characteristics that vary with watershed setting. We found that the environmental characteristics had the greatest effect on surface water-groundwater exchange and therefore denitrification, including streambed hydraulic conductivity, natural or background stream topography and slope, and groundwater levels. Type and number of instream structures also influenced surface water-groundwater exchange and denitrification, but to a lesser degree. Human effects at the watershed scale from agriculture and urbanization likely play a role in whether reach-scale restoration practices succeed in achieving water quality goals both through effect on exchange itself (e.g., altering bed sediment texture) and on nitrate sources. More broadly, restoration efforts at the watershed scale itself, such as reducing fertilizer use or improving stormwater management, may be necessary to achieve ambitious water quality goals. Nevertheless, reach-scale restoration efforts such as in-stream structures may play a useful role in certain watershed settings, for example where groundwater conditions induce neither strong gaining nor strong losing conditions. The interaction of reach-scale modifications and watershed setting must be understood to optimize nutrient removal from stream restoration through enhanced hyporheic exchange.

Integrating process‐based flow and temperature models to assess riparian forests and temperature amelioration in salmon streams

AbstractThe importance of riparian tree cover in reducing energy inputs to streams is increasingly recognized in schemes to mitigate climate change effects and protect freshwater ecosystems. Assessing different riparian management strategies requires catchment‐scale understanding of how different planting scenarios would affect the stream energy balance, coupled with a quantitative assessment of spatial patterns of streamflow generation. Here, we use the physically based MIKE SHE model to integrate simulations of catchment‐scale run‐off generation and in‐stream hydraulics with a heat transfer model. This was calibrated to model the spatio‐temporal distribution of hourly stream water temperature during warm low flow periods in a Scottish salmon stream. The model was explored as a “proof of concept” for a tool to investigate the effects of riparian management on high stream water temperatures that could affect juvenile Atlantic salmon. Uncertainty was incorporated into the assessment using the generalized likelihood uncertainty estimation approach. Results showed that by decreasing both the warming (daylight hours) and the cooling (night‐time hours) rates, forest cover leads to a reduction of the temperature range (with a delay of the time to peak by up to 2 hr) and can therefore be effectively used to moderate projected climate change effects. The modelling presented here facilitated the quantification of potential mitigating effects of alternative riparian management strategies and provided a valuable tool that has potential to be utilized as an evidence base for catchment management guidance.

Delay in catchment nitrogen load to streams following restrictions on fertilizer application

A MIKE SHE hydrological-solute transport model including nitrate reduction is employed to evaluate the delayed response in nitrogen loads in catchment streams following the implementation of nitrogen mitigation measures since the 1980s. The nitrate transport lag times between the root zone and the streams for the period 1950–2011 were simulated for two catchments in Denmark and compared with observational data. Results include nitrogen concentration and mass discharge to streams. By automated baseflow separation, stream discharge was separated into baseflow and drain flow components, and the nitrogen concentration and mass discharge in baseflow and drain flow were determined. This provided insight on the development of stream nitrogen loads, with a short average lag time in drain flow and a long average lag time in baseflow. The long term effect of nitrogen mitigation measures was determined, with results showing that there is a 15 years long delay in the appearance of peak nitrogen loads in streams. This means that real time stream monitoring data cannot be used alone to assess the effect of nitrogen mitigation measures.

Suitability of common models to estimate hydrology and diffuse water pollution in North-eastern German lowland catchments with intensive agricultural land use

Various process-based models are extensively being used to analyze and forecast catchment hydrology and water quality. However, it is always important to select the appropriate hydrological and water quality modeling tools to predict and analyze the watershed and also consider their strengths and weaknesses. Different factors such as data availability, hydrological, hydraulic, and water quality processes and their desired level of complexity are crucial for selecting a plausible modeling tool. This review is focused on suitable model selection with a focus on desired hydrological, hydraulic and water quality processes (nitrogen fate and transport in surface, subsurface and groundwater bodies) by keeping in view the typical lowland catchments with intensive agricultural land use, higher groundwater tables, and decreased retention times due to the provision of artificial drainage. In this study, four different physically based, partially and fully distributed integrated water modeling tools, SWAT (soil and water assessment tool), SWIM (soil and water integrated model), HSPF (hydrological simulation program– FORTRAN) and a combination of tools from DHI (MIKE SHE coupled with MIKE 11 and ECO Lab), have been reviewed particularly for the Tollense River catchment located in North-eastern Germany. DHI combined tools and SWAT were more suitable for simulating the desired hydrological processes, but in the case of river hydraulics and water quality, the DHI family of tools has an edge due to their integrated coupling between MIKE SHE, MIKE 11 and ECO Lab. In case of SWAT, it needs to be coupled with another tool to model the hydraulics in the Tollense River as SWAT does not include backwater effects and provision of control structures. However, both SWAT and DHI tools are more data demanding in comparison to SWIM and HSPF. For studying nitrogen fate and transport in unsaturated, saturated, and river zone, HSPF was a better model to simulate the desired nitrogen transformation and transport processes. However, for nitrogen dynamics and transformations in shallow streams, ECO Lab had an edge due its flexibility for inclusion of user-desired water quality parameters and processes. In the case of SWIM, most of the input data and governing equations are similar to SWAT but it does not include water bodies (ponds and lakes), wetlands and drainage systems. In this review, only the processes that were needed to simulate the Tollense River catchment were considered, however the resulted model selection criteria can be generalized to other lowland catchments in Australia, North-western Europe and North America with similar complexity.

Simulation of the minimum annual river flows based on the RCP climatic scenario, time horizon up to 2060-2080 and the Kaczawa River

In this paper a new simulations of minimum daily flow for Kaczawa River a left side tributary of the Odra River in south-west Poland are presented. Generated data were made based on very long series of 35 years of observed data and 24 sites of meteorological stations for south-west Poland gathered from the the Institute of Meteorology and Water Management National Research Institute (IMGW). For the data generation the spatial weather generator SWGEN producing the multisite daily time series was applied. Data were generated for the present (the year 2000 are used as a background) as well for future climate condition for 2060 and 2080 according Representative Concentration Pathways (RCPs) scenarios. The flow simulation in the river catchment is made using MIKE SHE hydrological model. Simulations are done for 2060 and 2080. The large number of new simulated series determined by the lead time, two climate change scenarios (RCP4.5 and RCP6.0), and number of generated years (1000 for each case) is equal to 5000 for a single station. Finally, Lognormal Pdf function for the minimum flow is presented as well probability of exceedance of minimum values.

Application of MIKE SHE to study the impact of coal mining on river runoff in Gujiao mining area, Shanxi, China.

Coal mining is one of the core industries that contribute to the economic development of a country but deteriorate the environment. Being the primary source of energy, coal has become essential to meet the energy demand of a country. It is excavated by both opencast and underground mining methods and affects the environment, especially hydrological cycle, by discharging huge amounts of mine water. Natural hydrological processes have been well known to be vulnerable to human activities, especially large scale mining activities, which inevitably generate surface cracks and subsidence. It is therefore valuable to assess the impact of mining on river runoff for the sustainable development of regional economy. In this paper, the impact of coal mining on river runoff is assessed in one of the national key coal mining sites, Gujiao mining area, Shanxi Province, China. The characteristics of water cycle are described, the similarities and differences of runoff formation are analyzed in both coal mining and pre-mining periods. The integrated distributed hydrological model named MIKE SHE is employed to simulate and evaluate the influence of coal mining on river runoff. The study shows that mining one ton of raw coal leads to the reduction of river runoff by 2.87 m3 between 1981 and 2008, of which the surface runoff decreases by 0.24 m3 and the baseflow by 2.63 m3. The reduction degree of river runoff for mining one ton of raw coal shows an increasing trend over years. The current study also reveals that large scale coal mining initiates the formation of surface cracks and subsidence, which intercepts overland flow and enhances precipitation infiltration. Together with mine drainage, the natural hydrological processes and the stream flows have been altered and the river run off has been greatly reduced.

Bias-aware data assimilation in integrated hydrological modelling

Abstract One of the major challenges in hydrological data assimilation applications is the presence of bias in both models and observations. The present study uses the ensemble transform Kalman filtering (ETKF) method and an observational bias estimation technique to estimate groundwater hydraulic heads. The study was carried out in a relatively complex, groundwater dominated, catchment in Denmark using the MIKE SHE model code. The method is implemented and evaluated using synthetic data and subsequently tested against real observations. The results from the synthetic experiments show that the bias-aware filter outperforms the standard filter, with improved state estimate and correct bias estimate. The assimilation using real observations further demonstrates the robustness of bias-aware ETKF, and the potential improvements using integrated hydrological modelling. Furthermore, the experiments with assimilating over different depths show that the state estimates depend on correlation across layers.

Probabilistic flood risk analysis considering morphological dynamics and dike failure

A comprehensive flood risk assessment should aim not only at quantifying uncertainties but also the variability of risk over time. In this study, an efficient modelling framework was proposed to perform probabilistic hazard and risk analysis in dike-protected river systems accounting for morphological variability and uncertainty. The modelling framework combined the use of: (1) continuous synthetic discharge forcing, (2) a stochastic dike breach model dynamically coupled to a stochastic unsteady one-dimensional hydraulic model (MIKE1D) describing river flows, (3) a catalogue of pre-run probabilistic inundation maps (MIKE SHE) and (4) a damage and loss model (CAPRA). The methodology was applied using continuous simulations to a 45-km reach of the Upper Koshi River, Nepal, to investigate the changes in breach and flood hazards and subsequent risks after 2 and 5 years of probable river bed aggradation. The study results indicated an increase in annual average loss of 4% per year driven by changes in loss distribution in the most frequent loss return periods (20–500 years). The use of continuous simulations and dike breach model also provided a more robust estimation of risk metrics as compared to traditional binary treatment of flood defence and/or the direct association of flow with loss return periods. The results were helpful to illustrate the potential impacts of dynamic river morphology, dike failure and continuous simulation and their significance when devising flood risk study methodologies.

Water level observations from unmanned aerial vehicles for improving estimates of surface water–groundwater interaction

AbstractIntegrated hydrological models are usually calibrated against observations of river discharge and piezometric head in groundwater aquifers. Calibration of such models against spatially distributed observations of river water level can potentially improve their reliability and predictive skill. However, traditional river gauging stations are normally spaced too far apart to capture spatial patterns in the water surface, whereas spaceborne observations have limited spatial and temporal resolution. Unmanned aerial vehicles can retrieve river water level measurements, providing (a) high spatial resolution; (b) spatially continuous profiles along or across the water body, and (c) flexible timing of sampling. A semisynthetic study was conducted to analyse the value of the new unmanned aerial vehicle‐borne datatype for improving hydrological models, in particular estimates of groundwater–surface water (GW–SW) interaction. Mølleåen River (Denmark) and its catchment were simulated using an integrated hydrological model (MIKE 11–MIKE SHE). Calibration against distributed surface water levels using the Differential Evolution Adaptive Metropolis algorithm demonstrated a significant improvement in estimating spatial patterns and time series of GW–SW interaction. After water level calibration, the sharpness of the estimates of GW–SW time series improves by ~50% and root mean square error decreases by ~75% compared with those of a model calibrated against discharge only.

Land use as possible strategy for managing water table depth in flat basins with shallow groundwater

ABSTRACTIn flat plains groundwater affects agricultural production outcomes and risks. Agricultural land use decisions, however, may strongly impact groundwater levels available for production. This paper explores the scope for managing groundwater levels through land use decisions in a sub-basin of the Salado River in the Argentine Pampas, a very flat area that plays a key role in world agricultural production. A spatially distributed hydrological model implemented with MIKE SHE software was used to establish the impacts of different land uses on groundwater dynamics, and to assess the interdependencies among spatially close decision-makers sharing a water table (WT). Additionally, groundwater level changes in response to climate variability were quantified. We found land use has strong effects on WT levels both for oneself (e.g. pastures can lead to significant decreases (up to 4.5 m) in WT levels) and others, in the form of strong interdependencies that exist between farmers sharing a WT where land use decisions of one farmer effect groundwater level of neighbouring farms and vice versa. However, the effectiveness to control groundwater levels through land use decisions is subject to the rather unpredictable effects of rainfall variability. The results presented in this paper provide key insights in relation to physical and social aspects that should be considered for managing groundwater levels through land use decisions, in order to avoid negative and/or maximize positive effects on agricultural production.