Integrated Catchment Model Research Articles

Urban flooding simulation and flood risk assessment based on the InfoWorks ICM model: A case study of the urban inland rivers in Zhengzhou, China.

Urban flooding intensifies with escalating urbanization. This study focuses on Xiong'er river as the study area and couples a 1D/2D urban flooding model using InfoWorks ICM (Integrated Catchment Modeling). Ten scenarios are set respectively with a rainfall return period of 5a 10a, 20a, 50a, and 100a, alongside rainfall durations of 1 and 24 h. Subsequently, the H-V (hazard-vulnerability) method was applied to evaluate urban flooding risk. Three indicators were selected for each of hazard factors and vulnerability factors. The relative weight values of each indicator factor were calculated using the AHP method. The result shows that (1) flood depth, rate, and duration escalate with longer rainfall return periods, yet decrease as the duration of rainfall increases; (2) as the rainfall return period lengthens, the proportion of node overflow rises, whereas it diminishes with longer rainfall durations, leading to an overall overloaded state in the pipeline network; and (3) the distribution in the research area is mainly low-risk areas, with very few extremely high-risk. Medium to high-risk areas are mainly distributed on both sides of the river, in densely built and low-lying urban areas. This study demonstrates that the model can accurately simulate urban flooding and provide insights for flood analyses in comparable regions.

Management of the designed risk level of urban drainage system in the future: Evidence from haining city, China

The design of urban drainage infrastructure is mainly based on historical conditions. Under global warming, more intense precipitation extremes will pose severe risk to current infrastructure. The evaluation of where and by how much design standards need to change, is urgently needed to help maintain well-functioning drainage systems. In this study, we used climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and InfoWorks Integrated Catchment Modeling (ICM) to simulate urban flooding. According to the latest design standard of urban drainage infrastructure, we assess the risk of future urban flooding, and evaluate the effect and benefit of drainage infrastructure adaptation measures. The results showed that, under the shared socioeconomic pathway (SSP) 5–8.5 scenario, a 35% increase in extreme rainfall would be expected. Under a 1-in-30-year precipitation event, the maximum depth would increase by 5.59%, and the withdrawal time would rise by 2.94% in the future period, relative to the baseline level. After the enlargement of drainage infrastructure in local areas, 10% pipe enlargement has a better effect to reduce risk and higher benefits than 5% pipe enlargement. These findings provide valuable insights for policymakers in enhancing the drainage system and adapting to climate change.

Assessing Heavy Metal Contamination Using Biosensors and a Multi-Branch Integrated Catchment Model in the Awash River Basin, Ethiopia

Metal pollution in rivers from untreated industrial and domestic wastewater is a major issue in economically developing countries worldwide. The Awash River Basin in Ethiopia is one of those rivers that faces rising heavy metal concentrations due to poor wastewater management and loose law enforcement controlling effluent discharge into rivers. In this study, surface water and wastewater samples were collected within the Awash River Basin, with metals analysis using ICP-MS techniques. Acute toxicity of water was determined using new molecular biosensor technology based on engineered luminescent bacteria. A multi-branch Integrated Catchment Model (INCA) for metals, including Arsenic, Cadmium, Chromium, Copper, Lead, Manganese, and Zinc was applied to the Awash River Basin to simulate the impact of tannery discharge on the river water pollution levels and to evaluate a set of treatment scenarios for pollution control. Results show that all samples from tannery wastewater have high levels of metals, such as Chromium and Manganese with high levels of toxicities. River water samples from upper Awash near Addis Ababa showed elevated concentrations of heavy metals due to the untreated wastewater from the dense population and a large number of industries in that area. The modeling scenarios indicate that improved wastewater management will reduce the metal concentration significantly. With a 50% reduction in effluent concentrations, the mean concentrations of heavy metals (such as Chromium) over two years would be able to reach 20 to 50% reduction in river water samples.

Modelling Subarctic watershed dissolved organic carbon response to hydroclimatic regime

Shifts in hydroclimatic regimes associated with global climate change may impact freshwater availability and quality. In high latitudes of the northern hemisphere, where vast quantities of carbon are stored terrestrially, explaining landscape-scale carbon (C) budgets and associated pollutant transfer is necessary for understanding the impact of changing hydroclimatic regimes. We used a dynamic modelling approach to simulate streamflow, DOC concentration, and DOC export in a northern Canadian catchment that has undergone notable climate warming, and will continue to for the remainder of this century. The Integrated Catchment model for Carbon (INCA-C) was successfully calibrated to a multi-year period (2012–2016) that represents a range in hydrologic conditions. The model was subsequently run over 30-year periods representing baseline and two future climate scenarios. Average discharge is predicted to decrease under an elevated temperature scenario (22–27 % of baseline) but increase (116–175 % of baseline) under an elevated temperature and precipitation scenario. In the latter scenario the nival hydroclimatic regime is expected to shift to a combined nival and pluvial regime. Average DOC flux over 30 years is predicted to decrease (24–27 % of baseline) under the elevated temperature scenario, as higher DOC concentrations are offset by lower runoff. Under the elevated temperature and precipitation scenario, results suggest an increase in carbon export of 64–81 % above baseline. These increases are attributed to greater connectivity of the catchment. The largest increase in DOC export is expected to occur in early winter. These predicted changes in DOC export, particularly under a climate that is warmer and wetter could be part of larger ecosystem change and warrant additional monitoring efforts in the region.

Integrated flood management in the Hull catchment, England

Since the major flood event in 2007, RPS has been deeply involved in investigating, understanding and reducing flood risk across the Hull and Haltemprice catchment. RPS has developed and refined a complex integrated catchment model by combining Yorkshire Water's model of below-ground assets with data for the watercourses and overland flow paths obtained from the Environment Agency, East Riding of Yorkshire Council and Hull City Council. RPS used the model to identify major schemes, leading to the design of flood alleviation schemes at Willerby and Derringham, Anlaby and East Ella, and Cottingham and Orchard Park. With further enhancements, the model has been used to better understanding of the complex interactions between the various water systems and solutions are being identified for a long-term plan. Hull has many unique features, driven by its topography, geology and the historical developments of its sewerage network and waterways. These specific challenges require bespoke solutions and there is a clear desire among the partner organisations to work together to drive contemporary blue–green solutions. This requires multi-agency working and progressive thinking to deliver effective flood risk management. This paper reviews the challenges in understanding and resolving these issues.

Natural and anthropogenic sources of salinity in the Awash River and Lake Beseka (Ethiopia): Modelling impacts of climate change and lake-river interactions

Study region: Awash River Basin, Ethiopia: Study focusMany river basins in sub-Saharan Africa have become vulnerable due to the impact from climate change, weak governance and high levels of poverty. One of the primary concerns is the elevated salinity and the degradation of water quality in the Awash River. Located in the Great Rift Valley in Ethiopia, the Awash River has unique hydrochemistry due to water-rock interactions. However, in recent years, increasing anthropogenic activities including the discharge from saline Lake Beseka into the Awash River has caused some concern. This study used an Integrated Catchment Model to simulate chloride concentration in the Awash River Basin by taking both natural and anthropogenic sources of salinity into consideration. Future scenarios of climate change and Lake Beseka discharge were examined to assess the impact to the river water quality. New hydrologic insightsResults show that Lake Beseka has made significant contribution to the rise of the salinity in the Awash River. If the trend of human interference (e.g. increased irrigation and unregulated water transfer) continues, the river downstream of Lake Beseka could see Cl increases up to 200 % in the near future (2006–2030). The modeling results are essential for generating long term plans for proper utilization of water resources especially in the region where the resources and the economic capacity to meet the water demand is lacking.

Assessing the Effectiveness of Mitigation Strategies for Flood Risk Reduction in the Segamat River Basin, Malaysia

Flooding is a frequent, naturally recurring phenomenon worldwide that can become disastrous if not addressed accordingly. This paper aims to evaluate the impacts of land use change and climate change on flooding in the Segamat River Basin, Johor, Malaysia, with 1D–2D hydrodynamic river modeling, using InfoWorks Integrated Catchment Modeling (ICM). The study involved the development of flood maps for four different scenarios: (1) future land use in 2030; (2) the impacts of climate change; (3) three mitigation strategies comprising detention ponds, rainwater harvesting systems (RWHSs), and permeable pavers; and (4) a combination of these three mitigation strategies. The obtained results show increases in the flood peaks under both the land use change and climate change scenarios. With the anticipated increase in development activities within the vicinity up to 2030, the overall impact of urbanization on the extent of flooding would be rather moderate, as the upper and middle parts of the basin would still be dominated by forests and agricultural activities (approximately 81.13%). In contrast, the potential flood-inundated area is expected to increase from 12.25% to 16.64% under storms of 10-, 50-, 100-, and 1000-year average recurrence intervals (ARI). Interestingly, the simulation results suggest that only the detention pond mitigation strategy has a considerable impact on reducing floods, while the other two mitigation strategies have less flood reduction advantages for this agricultural-based rural basin located in a tropical region.

A New, Catchment-Scale Integrated Water Quality Model of Phosphorus, Dissolved Oxygen, Biochemical Oxygen Demand and Phytoplankton: INCA-Phosphorus Ecology (PEco)

Process-based models are commonly used to design management strategies to reduce excessive algal growth and subsequent hypoxia. However, management targets typically focus on phosphorus control, under the assumption that successful nutrient reduction will solve hypoxia issues. Algal responses to nutrient drivers are not linear and depend on additional biotic and abiotic controls. In order to generate a comprehensive assessment of the effectiveness of nutrient control strategies, independent nutrient, dissolved oxygen (DO), temperature and algal models must be coupled, which can increase overall uncertainty. Here, we extend an existing process-based phosphorus model (INtegrated CAtchment model of Phosphorus dynamics) to include biological oxygen demand (BOD), dissolved oxygen (DO) and algal growth and decay (INCA-PEco). We applied the resultant model in two eutrophied mesoscale catchments with continental and maritime climates. We assessed effects of regional differences in climate and land use on parameter importance during calibration using a generalised sensitivity analysis. We successfully reproduced in-stream total phosphorus (TP), suspended sediment, DO, BOD and chlorophyll-a (chl-a) concentrations across a range of temporal scales, land uses and climate regimes. While INCA-PEco is highly parameterized, model uncertainty can be significantly reduced by focusing calibration and monitoring efforts on just 18 of those parameters. Specifically, calibration time could be optimized by focusing on hydrological parameters (base flow, Manning’s n and river depth). In locations with significant inputs of diffuse nutrients, e.g., in agricultural catchments, detailed data on crop growth and nutrient uptake rates are also important. The remaining parameters provide flexibility to the user, broaden model applicability, and maximize its functionality under a changing climate.

Impacts of climate change and sea level rise on catchment management: A multi-model ensemble analysis of the Nerang River catchment, Australia

Estimating the most likely impacts of climate change on the hydrological conditions of catchments is essential for efficient future water management. This is particularly important in Southeast Queensland, Australia, which is projected to be significantly impacted by climate change. We have developed an integrated catchment modelling framework for the Nerang River catchment that combines a hydrologic model, a reservoir operation model, and a hydrodynamic river model. The multi-model ensemble is used to investigate eight General Circulation Models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5) under two representative concentration pathway scenarios (RCP 4.5 and RCP 8.5) over the baseline period (2000–2009) and one future period (2075–2084). Additionally, the tidal section of the Lower Nerang River was studied under coupled impacts of the RCP scenarios and sea level rise by 0.80 m. The ensemble projections over the future period present slight decreasing tendencies in the median of monthly long-term daily inflow to Hinze Dam in the upper Nerang River. Additionally, the average environmental releases of 7.25 ML/day are expected to reduce over the future period by 6.02% and 5.37% under RCP 4.5 and RCP 8.5, respectively compared to the baseline period. The hydrodynamic model results revealed that sea level rise is projected to have significant impact on water level variations at two river flooding alert sites, Carrara Alert and Evandale Alert. As a result, a 0.80 m sea level rise can increase ensemble water level projections by almost 0.75 m and 0.80 m at Carrara Alert and Evandale Alert sites, respectively, which will cause minor to major flooding events at Evandale Alert site. The outcomes of the present paper can assist the decision-makers and the community of the Nerang River catchment with a robust tool to evaluate climate change scenarios for sustainable future water resources management and allocation. • • An integrated catchment modelling framework was developed for SEQ, Australia. • • A hydrologic, reservoir, and a hydrodynamic river models were combined. • • Outputs from eight CMIP5 models and two RCPs were used for future projections. • • Slight decreases in dam inflow are projected in the future. • • Decreasing trends in environmental flow release are expected under climate change.

The effects of surface pollution on urban river water quality under rainfall events in Wuqing district, Tianjin, China

A large quantity of pollutants is washed off by stormwater during rainfall events. Polluted storm runoff deteriorates the water quality of receiving water bodies, which is becoming a main threat to urban water environment. In this work, five rainfall events were monitored to clarify the characteristics of land surface pollution in Wuqing district, China. Four pollutant indicators of storm runoff samples, including chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH3-N), were analyzed and then used to validate the parameters of a model established by Infoworks integrated catchment modeling (ICM). The land surface pollutant loads of metropolitan area for four different rainfall scenarios and the variations in pollutants concentration in urban rivers were illustrated based on the model. The simulated results showed that the volume of runoff increased from 31.8 × 104 m3 to 139.7 × 104 m3 with the increase in the return period. The EMCs (Event Mean Concentration) of pollutants, however, were negatively correlated with return periods and the maximum drop was approximately 67%. Furthermore, the increased runoff enhanced the dilution effect and reduced the residence time of pollutants in rivers, which were the main reasons for the decrease of the pollutants concentrations. The results suggested that the runoff should be taken into account when considering the effects of surface pollution on urban river water quality.

Improved method for identifying Manning’s roughness coefficients in plain looped river network area

Manning’s roughness coefficient(n) is considered a key parameter in a one-dimensional (1D) hydrodynamic model. However, it is highly variable and time- and site- dependent. Further, identifying proper n values is not easy, especially in plain looped river network areas. Therefore, a more systematic approach is needed. This study proposes a coupled optimization-simulation model to systematically estimate the spatial distribution of n values. The particle swarm optimization (PSO) algorithm and InfoWorks Integrated Catchment Modelling (ICM) software were integrated to solve the objective function and hydraulic process, respectively. Crisscrossing rivers were partitioned into river reaches that were each assumed to have a uniform and constant Manning’s roughness coefficient according to their network topology and cross-section variation. In addition, a sensitivity analysis was implemented to determine the weights of measured data from different gauging stations, and a large difference in the spatial distribution of the sensitivity index illustrated the importance of identifying the weights of multiple stations. Then, a systematic approach was applied to estimate the n values in the Changshu Grand Polder Area (CGPA), which is crisscrossed by 150 rivers, under the water diversion stage. The calculation statistics and efficiency indicated that the proposed method performs well for model calibration.

Flood Mitigation Measures in Urban Areas of Malaysia Using the Integrated Catchment Modelling Approach

Integrated catchment modelling has been used to provide non-structural measures for the mitigation and management of urban flood prone areas. This paper aims to demonstrate a model-based approach through flood mapping that generates multiple simulation results of flood mitigation alternatives for the Sungai Gombak basin. Hydrological and hydraulic analysis, as well as hydrodynamic modelling were carried out using Infoworks Integrated Catchment Modelling (ICM) to evaluate the changes of flood extent caused by different structural components. Rainfall analyses were carried out through the computation of rainfall-runoff and design storms at various return periods and durations. Historical rainfall and stage data were used in the calibration process before the design storm events were fed into the hydrological model. Simulation of the design floods were run under different return periods, storm durations, and land use conditions. The results show that the existing rivers downstream of Sungai Gombak can only provide a flood protection level of 5 to 20-year Average Recurrence Intervals (ARIs). The main cause of frequent flooding can be attributed to the rapid change in catchment land use as development has far exceeded the Kuala Lumpur Structure Plan 2020, and the lack of compliance to the practices recommended in Manual Saliran Mesra Alam (MSMA). The findings suggest that bridge constriction removal is the key solution and that its combination with other flood mitigation works would significantly reduce the flood levels. In conclusion, the study provides useful results and a technical proposal for the authority, and successfully recommends further improvements in flood mapping practices for future studies.

Modelling heavy metals in the Buriganga River System, Dhaka, Bangladesh: Impacts of tannery pollution control

Heavy metal pollution from tanneries is a global problem in many rapidly developing economies. Effluent discharges into rivers cause serious problems for water quality, damaging ecology and threatening the livelihoods of people, especially in developing urban centres which often have a high concentration of factories. The industry intensive capital area of Bangladesh is impacted with high levels of metals pollution in rivers in the Greater Dhaka Watershed. Sampling and modelling studies have been undertaken to assess pollution in the Buriganga River System in Dhaka. The process based, dynamic model INCA (Integrated Catchments) model has been used to simulate metals along the Buriganga River System in Central Dhaka. Observed and simulated metals concentrations are high, and the model shows that the proposed transfer of the tannery industry upstream helps to reduce the pollution significantly downstream. However, moving the industry upstream may be counterproductive as it is discharged into the upper reaches of the river. This will create pollution upstream unless the newly constructed effluent treatment system can operate at a high level.

Modelling the hydrological processes of a Chinese lowland polder and identifying the key factors using an improved PHPS model

Improved hydrological processes simulation and identification of determinants are urgently needed in risk management to reduce socio-economic losses resulting from polder water problems. This paper improved the lowland Polder Hydrology and Phosphorus modelling System (called PHPS2.0) by coupling the PHPS, Modified Universal Soil Loss Equation (MUSLE), and Integrated Catchments model of Phosphorus dynamics (INCA-P). Then, based on the PHPS2.0 and data collected from the Jianwei polder in southeastern China, a boosted regression tree (BRT) algorithm was used to explore the key factors determining the temporal variations in polder discharge and phosphorus export. The results showed that PHPS2.0 achieved excellent agreements between the simulated and observed discharge, surface water and phosphorus. The model performance was significantly improved because field-scale phosphorus dynamics were considered. The water and phosphorus balances exhibited substantial seasonal changes, especially in terms of fertilization, crop harvest, and discharge. The temporal change in catchment discharge mainly depended on precipitation and evaporation, which accounted for 63.7% of the discharge variations. In contrast, the temporal variation in phosphorus export was determined by the crop cover and fertilizer application, which accounted for 75.4% of the phosphorus variation. To mitigate the phosphorus loss to downstream freshwater, it is recommended to remain crop residues, reduce the overuse of phosphorus chemical fertilizers, and draft emergency plans. This study expands the knowledge of the relationship between polder environmental factors and hydrological processes and provides guidance for pollution controls.

Uncertainty analysis in a large-scale water quality integrated catchment modelling study

Receiving water quality simulation in highly urbanised areas requires the integration of several processes occurring at different space-time scales. These integrated catchment models deliver results with a significant uncertainty level associated. Still, uncertainty analysis is seldom applied in practice and the relative contribution of the individual model elements is poorly understood. Often the available methods are applied to relatively small systems or individual sub-systems, due to limitations in organisational and computational resources. Consequently this work presents an uncertainty propagation and decomposition scheme of an integrated water quality modelling study for the evaluation of dissolved oxygen dynamics in a large-scale urbanised river catchment in the Netherlands. Forward propagation of the measured and elicited uncertainty input-parametric distributions was proposed and contrasted with monitoring data series. Prior ranges for river water quality-quantity parameters lead to high uncertainty in dissolved oxygen predictions, thus the need for formal calibration to adapt to the local dynamics is highlighted. After inferring the river process parameters with system measurements of flow and dissolved oxygen, combined sewer overflow pollution loads became the dominant uncertainty source along with rainfall variability. As a result, insights gained in this paper can help in planning and directing further monitoring and modelling efforts in the system. When comparing these modelling results to existing national guidelines it is shown that the commonly used concentration-duration-frequency tables should not be the only metric used to select mitigation alternatives and may need to be adapted in order to cope with uncertainties.

Water quality modelling of the Mekong River basin: Climate change and socioeconomics drive flow and nutrient flux changes to the Mekong Delta

The Mekong delta is recognised as one of the world's most vulnerable mega-deltas, being subject to a range of environmental pressures including sea level rise, increasing population, and changes in flows and nutrients from its upland catchment. With changing climate and socioeconomics there is a need to assess how the Mekong catchment will be affected in terms of the delivery of water and nutrients into the delta system. Here we apply the Integrated Catchment model (INCA) to the whole Mekong River Basin to simulate flow and water quality, including nitrate, ammonia, total phosphorus and soluble reactive phosphorus. The impacts of climate change on all these variables have been assessed across 24 river reaches ranging from the Himalayas down to the delta in Vietnam. We used the UK Met Office PRECIS regionally coupled climate model to downscale precipitation and temperature to the Mekong catchment. This was accomplished using the Global Circulation Model GFDL-CM to provide the boundary conditions under two carbon control strategies, namely representative concentration pathways (RCP) 4.5 and a RCP 8.5 scenario. The RCP 4.5 scenario represents the carbon strategy required to meet the Paris Accord, which aims to limit peak global temperatures to below a 2 °C rise whilst seeking to pursue options that limit temperature rise to 1.5 °C. The RCP 8.5 scenario is associated with a larger 3–4 °C rise. In addition, we also constructed a range of socio-economic scenarios to investigate the potential impacts of changing population, atmospheric pollution, economic growth and land use change up to the 2050s. Results of INCA simulations indicate increases in mean flows of up to 24%, with flood flows in the monsoon period increasing by up to 27%, but with increasing periods of drought up to 2050. A shift in the timing of the monsoon is also simulated, with a 4 week advance in the onset of monsoon flows on average. Decreases in nitrogen and phosphorus concentrations occur primarily due to flow dilution, but fluxes of these nutrients also increase by 5%, which reflects the changing flow, land use change and population changes.

Temporal Variation and Reduction Strategy of Nutrient Loads from an Urban River Catchment into a Eutrophic Lake, China

Excessive nutrient input from urban areas increases the occurrence of eutrophication. Control of nutrient loads is perceived as the primary restoration method. Quantifying temporal variation of nutrient loads is essential to understand the dynamic relationships of nutrient source-impacts in the urban water system and investigate the operational efficiency of treatment facilities for eutrophication control. Here, a holistic approach was developed to estimate nutrient loads from different sources and evaluate nutrient impacts on the urban water environment. An integrated catchment model of nutrient loads was built and applied to calculate river nutrient loads from untreated rainfall runoff, untreated sewage, and treated recharge into the eutrophic Dianchi Lake from an urban river catchment with limited infrastructure. Nutrient impacts on the lake were evaluated and a load reduction strategy was given a hint to reduce nutrient impacts of urban rivers. During the study period 2014–2016, nutrient loads from the urban river generally decreased except during heavy winter rainfall events and high-intensity pollution events associated with rainfall runoff. The average contribution of annual nutrient loads to the lake capacity indicated the underestimation of nutrient impacts of urban rivers. This approach provides new insights into urban water management and underscores the importance of sewage infrastructure.

Modeling impacts of climate and land use change on streamflow, nitrate, and ammonium in the Kor River, southwest of Iran

Abstract This study examined the separate and combined impacts of future changes in climate and land use on streamflow, nitrate and ammonium in the Kor River Basin, southwest of Iran, using the representative concentration pathway 2.6 and 8.5 scenarios of the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). Different land use and climate change scenarios were used and the streamflow, nitrate and ammonium in the future period (2020–2049) under these scenarios were simulated by Integrated Catchment Model for Nitrogen (INCA–N). Results indicated that climate change will increase streamflows and decrease nitrate and ammonium concentrations in summer and autumn. Land use changes were found to have a little impact on streamflows but a significant impact on water quality, particularly under an urban development scenario. Under combined scenarios, larger seasonal changes in streamflows and mixed changes of nitrate and ammonium concentrations were predicted.

Submarine and intertidal groundwater discharge through a complex multi-level karst conduit aquifer

The quantification of submarine and intertidal groundwater discharge (SiGD) or purely submarine groundwater discharge (SGD) from coastal karst aquifers presents a major challenge, as neither is directly measurable. In addition, the expected heterogeneity and intrinsic structure of such karst aquifers must be considered when quantifying SGD or SiGD. This study applies a set of methods for the coastal karst aquifer of Bell Harbour in western Ireland, using long-term onshore and offshore time series from a high-resolution monitoring network, to link catchment groundwater flow dynamics to groundwater discharge as SiGD. The SiGD is estimated using the “pollution flushing model”, i.e. a mass-balance approach, while catchment dynamics are quantified using borehole hydrograph analysis, single-borehole dilution tests, a water balance calculation, and cross-correlation analysis. The results of these analyses are then synthesised, describing a multi-level conduit-dominated coastal aquifer with a highly fluctuating overflow regime draining as SiGD, which is in part highly correlated with the overall piezometric level in the aquifer. This concept was simulated using a hydraulic pipe network model built in InfoWorks ICM [Integrated Catchment Modeling]® version 7.0 software (Innovyze). The model is capable of representing the overall highly variable discharge dynamics, predicting SiGD from the catchment to range from almost 0 to 4.3 m3/s. The study emphasises the need for long-term monitoring as the basis for any discharge studies of coastal karst aquifers. It further highlights the fact that multiple discharge locations may drain the aquifer, and therefore must be taken into consideration in the assessment of coastal karst aquifers.

Modeling future flows of the Volta River system: Impacts of climate change and socio-economic changes

As the scientific consensus concerning global climate change has increased in recent decades, research on potential impacts of climate change on water resources has been given high importance. However in Sub-Saharan Africa, few studies have fully evaluated the potential implications of climate change to their water resource systems. The Volta River is one of the major rivers in Africa covering six riparian countries (mainly Ghana and Burkina Faso). It is a principal water source for approximately 24 million people in the region. The catchment is primarily agricultural providing food supplies to rural areas, demonstrating the classic water, food, energy nexus. In this study an Integrated Catchment Model (INCA) was applied to the whole Volta River system to simulate flow in the rivers and at the outlet of the artificial Lake Volta. High-resolution climate scenarios downscaled from three different Global Climate Models (CNRM-CM5, HadGEM2-ES and CanESM2), have been used to drive the INCA model and to assess changes in flow by 2050s and 2090s under the high climate forcing scenario RCP8.5. Results show that peak flows during the monsoon months could increase into the future. The duration of high flow could become longer compared to the recent condition. In addition, we considered three different socio-economic scenarios. As an example, under the combined impact from climate change from downscaling CNRM-CM5 and medium+ (high economic growth) socio-economic changes, the extreme high flows (Q5) of the Black Volta River are projected to increase 11% and 36% at 2050s and 2090s, respectively. Lake Volta outflow would increase +1% and +5% at 2050s and 2090s, respectively, under the same scenario. The effects of changing socio-economic conditions on flow are minor compared to the climate change impact. These results will provide valuable information assisting future water resource development and adaptive strategies in the Volta Basin.