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This study proposes a novel generalized storage function (GSF) model for water level estimation from the rating curve relationship by considering (i) the spatial distribution of rainfall over the basin and (ii) incorporating all the possible inflow and outflow components to reduce the uncertainties involved. The proposed GSF model, along with three other models, was then applied in two watersheds of Japan to examine its applicability in different types of watersheds with optimized parameters: (i) the Iga watershed, a semi-urban watershed and (ii) the Oto watershed, a rural watershed. Further, the proposed model’s effectiveness was identified based on hydrograph reproducibility, Akaike information criterion, and Akaike weight. The results showed that the GSF model performed well in both watersheds compared to the other models. Moreover, the Morris global sensitivity method has used to analyze the sensitivity of the GSF model parameters for the objective function of root mean square error.

Planning and prioritization in flood disaster risk reduction (FDRR) is critical and often tedious to both planners and decision‐makers. In Metro Manila, Philippines, flooding is a perennial problem that requires regular assessments and updating of its municipal‐based FDRR management systems. A simple, but practical approach may prove useful in the identification of priority schemes, especially when the need for improvement is urgent and resources are limited. This study provides a simple quantitative approach to gaps assessment for FDRR management systems using a fuzzy multiattribute decision‐making technique. This is demonstrated by utilizing the stakeholders’ perceptions and field information obtained during the aftermath of the tropical storm Ketsana in 2009. Study results show that the gaps can be quantified and ranked to establish the priority schemes for the improvement of the FDRR management systems in Metro Manila, focusing mainly on the following FDRR management systems: prevention, preparedness, response and disaster recovery.

Groundwater plays a key role in public water supplies around the world, and consideration of the social dimension is a key issue in sustainable groundwater management. In Hanoi, the capital of Vietnam, the situation of groundwater resources is disastrous because the quality has seriously degraded recently. Hence, in this study, a social sustainability assessment framework of groundwater resources with a focus on Hanoi is proposed for the first time. An analytical hierarchy process (AHP) approach was used to generate the main components (aspects and indicators) of this framework, which has been considered one of the most challenging tasks in AHP sustainability applications. To overcome these challenging tasks, we carefully reviewed and explored the current problems of Hanoi groundwater resources to propose 3 main aspects (quantity, quality, and management) and appropriately selected their 13 sustainability indicators for this target area. We introduce a sustainability index function (SIF) for indicators to clarify the relationship between each indicator value and its sustainability index. Furthermore, we consider both the conventional linear relationship, as it is usually developed in the literature, as well as a non-linear SIF to arrive at a reasonable sustainability assessment. For the Hanoi case study, the sustainability indices obtained using a combined linear and non-linear SIF method reflect the current problems well, that is, the social sustainability assessment is closer to reality. The sustainability indices of the quantity, quality, and management aspects of the groundwater were appropriately assessed as good, poor, and acceptable, respectively, resulting in Hanoi being rated at the acceptable level in the final social sustainability assessment. This result reveals that the population of Hanoi is satisfied with the quantity of water but dissatisfied with its current poor quality and its relatively high price.

Rapid urbanization is considered to be an important factor that contributes to flood risk. Therefore, flood prediction in urban watersheds using appropriate runoff models is essential to avoid the harmful effects of floods. There are various storage function (SF) models such as Kimura, Prasad, Hoshi, and urban storage function (USF) models that have been widely used in different parts of the world as rainfall-runoff models in which the USF model was recently developed in Japan for the specific application in urban watersheds. However, the identification of an appropriate model remains challenging in the field of hydrology. Therefore, this study aims to identify an effective SF model for an urban watershed in terms of hydrograph reproducibility and from an Akaike information criterion (AIC) perspective. The SCE-UA global optimization method was used for the parameter optimization of each model with root mean square error (RMSE) as the objective function. The reproducibility of the hydrograph was evaluated using the performance evaluation criteria of RMSE, Nash-Sutcliffe efficiency (NSE), and other error functions of peak, volume, time to peak, lag time, and runoff coefficient. The results revealed that the higher values of NSE coupled with the lower values of RMSE and other error functions indicated that the hydrograph reproducibility of USF is the highest among the SF models. Furthermore, AIC and Akaike weight (AW) were used to identify the most effective model among all those based on the information criteria perspective. The USF model received the lowest AIC score and the highest AW during most of the events, which indicates that it is the most parsimonious model compared to the other SF models. Moreover, uncertainty characterization of the SF model parameters was also conducted to analyze the effect of each parameter on model performance.

This study proposes an approach in conducting an overall performance evaluation of the integrated flood risk management (IFRM). The proposed approach is a monitoring & evaluation (M&E) framework for IFRM suitable in data-poor areas. The proposed framework has two main tasks: 1) to monitor the measures of the four IFRM strategies (prevention, preparedness, response, and recovery/rehabilitation) by asking experts for qualitative appraisals and 2) to evaluate the monitored measures using fuzzy based multi-criteria evaluation based on priority ranking methodology (FME-PRM). The M&E framework is applied for Metro Manila, Philippines, as a case study, where it enabled the quantification of qualitative data and provided a systematic solution for the weight assignment on the IFRM strategies and measures in Metro Manila. The results successfully show the IFRM performance level at the 13 cities and Metro Manila as a region. The results reveal that Metro Manila is at the “Good” performance level, which indicates that IFRM implementation had already progressed, but the achievements are not yet substantial.

The mining sector faces some of the most difficult sustainability challenges of any industrial sector. The mining sector is remarkably significant to the development of the Asia-Pacific Economic Cooperation (APEC) region, because the majority of global trade and investment in this region depends on this sector. Therefore, the assessment of mining sector sustainability at national and global scales in APEC economies is an important task. So far, however, mining sector sustainability assessment frameworks have only been developed at small scales, such as companies and cities. In this study, therefore, it is proposed an indicator-based sustainability assessment framework (iSAF) to assess mining sector sustainability at national and global scales. In this framework, fuzzy logic was utilized to adequately deal with the uncertainty and vagueness of human expressions. The conventional fuzzy scales were suitably modified in the proposed framework to facilitate confident decision-making by the relevant stakeholders. In order to avoid repeatedly conducting the judgment until the acceptable consistency was obtained, iSAF implemented an innovative theory to deal with unacceptable consistencies in judgment. The proposed iSAF was applied to the mining sector of APEC economies using data from the APEC 2010 Project. As for the results, three important criteria including economic, environmental, and social criteria and twenty significant indicators were appropriately selected to cover the actual situation in the sector. The results showed that iSAF was a suitable framework for preventing uncertainty and vagueness in decision-making. iSAF was found to provide crucial support to decision-makers, not only in identifying and structuring the main components contributing to sustainability, but also in pointing out the factors in which significant investment should be made to effectively improve sustainability.

In this study, the high-resolution polygonal land cover data of EEA Urban Atlas was applied for land-use characterization in the dynamic multi-basin hydrological model, HYPE. The objective of the study was to compare this dedicated urban land cover data in semi-distributed hydrological modelling with the widely used but less detailed EEA CORINE. The model was set up for a basin including a small town named Svedala in southern Sweden. In order to verify the ability of the HYPE model to reproduce the observed flow rate, the simulated flow rate was evaluated based on river flow time series, statistical indicators and flow duration curves. Flow rate simulated by the model based on Urban Atlas generally agreed better with observations of summer storm events than the CORINE-based model, especially when the daily rainfall amount was 10 mm/day or more, or the flow exceedance probability was 0.02 to 0.5. It suggests that the added value of the Urban Atlas model is higher for heavy-to-medium storm events dominated by direct runoff. To conclude, the effectiveness of the proposed approach, which aims at improving the accuracy of hydrological simulations in urbanized basins, was supported.

When applying a distributed hydrological model in urban watersheds, grid-based land-use classification data with 10 m resolution are typically used in Japan. For urban hydrological models, the estimation of the impervious area ratio (IAR) of each land-use classification is a crucial factor for accurate runoff analysis. In order to assess the IAR accurately, we created a set of vector-based “urban landscape GIS delineation” data for a typical urban watershed in Tokyo. By superimposing the vector-based delineation map on the grid-based map, the IAR of each grid-based land-use classification was estimated, after calculating the IARs of all grid cells in the entire urban watershed. As a result, we were able to calculate the frequency distribution of IAR for each land-use classification, as well as the spatial distribution of IARs for the urban watershed. It is evident from the results that the reference values of IAR for the land-use classifications were estimated very roughly and inherited errors of ...

Many countries encountered “barriers” or obstacles that hampered the process of adapting to the integrated flood risk management (IFRM) from the traditional hard structural solutions in managing urban flooding. One of the crucial tasks to overcome the barriers is to understand their interrelationships. However, analysis of the interrelationships between the barriers to IFRM adaptation has not been carried out yet. This study attempts to analyze the interrelationships between the barriers to IFRM adaptation using the Interpretive Structural Modeling (ISM) method. The barriers in Metro Manila, a megacity in a developing country, were identified first in this study. Then, the ISM method was slightly modified and applied to analyze the interrelationships of the identified barriers. As a result, we identified 12 barriers which are relatively numerous compared with the developed countries, and so we categorized them into the governance, social, and technological resources aspects. Through the application of the ISM method, the interrelationships of the barriers to IFRM adaptation were systematically analyzed for the first time while also showing their hierarchical diagram. The results of the ISM reveal that barriers in the governance aspect are the most influential in which the lack of a sole organizing body is the most influential barrier. The barriers in the technological resources aspect are the second most influential, while barriers in the social aspect are the least influential and most dependent barriers. The approach presented in this study can be useful for decision makers and practitioners in understanding the interrelationships between the barriers.

There is mounting concern about how to support decision-makers in driving sustainable water resources management; science needs to support the decision-making process to promote evidence-based decisions. To this end, sustainability assessment is considered a useful technique, which provides enough information to assist management. This study proposed a groundwater sustainability assessment framework, which is developed from a regular sustainability assessment approach and analytical hierarchy process (AHP). In the proposed framework, the three main pillars (environmental, social, and economic) of the concept of sustainability were considered the three important sustainability criteria. Hence, we demonstrated the proposed framework for a Hanoi case study with focus on the environmental sustainability criterion. The concept of AHP was used to create the main sustainability components (the three criteria, associated with their aspects and indicators) of a hierarchy, which appropriately cover environmental sustainability issues of groundwater resources in the target area. Based on the available reliable data of the current problems in Hanoi, we proposed three main sustainability aspects (quantity, quality, and management) and, accordingly, selected their twelve environmental sustainability indicators. To determine a reasonable sustainability assessment, we considered a conventional linear and non-linear relationship between the indicators and the corresponding sustainability indices. As for the results from the Hanoi case study, the environmental sustainability indices obtained from using a combined linear and non-linear relationship case appropriately reflect the current situation, that is, the environmental sustainability assessment is close to reality. The sustainability indices of the quantity, quality, and management aspects of groundwater were appropriately assessed at acceptable levels, resulting in Hanoi being rated at the acceptable level in the final environmental sustainability index. The variability of the environmental sustainability indices indicated that the current groundwater abstraction networks are heavily concentrated in a few specific areas in Hanoi, which is not optimal for utilizing the rich natural recharge resources of the area. Improvement of the current poor groundwater quality and strict enforcement of environmental regulations are essential to enhancing the environmental sustainability and, more importantly, to drive Hanoi towards sustainable groundwater resources.

In Tokyo metropolitan area, flood risk is increasing due to social and environmental conditions including concentration of population and industry etc. Small urban watersheds are at a high risk of inundation by river flooding and/or inner water induced by heavy rainfall in a short time. To estimate river water level accurately in urban small rivers, it is critically important to conduct precise runoff analysis by using spatiotemporally distributed rainfall data. In this study, a runoff analysis was conducted with spatiotemporally densely distributed X-band MP Radar (X-band multi-parameter radar) data as input for storm events occurred in upper Kanda River, a typical urban small river in Tokyo. Then, SCE-UA method, one of global optimization methodologies, was applied to identify the parameters of the storm runoff model. The results revealed that urban storm runoff was predicted accurately using X-band MP radar map supported by optimized runoff model.

Groundwater has been the primary source of daily water supplies for people living in the Red River Delta, the second largest delta in Vietnam. For this reason, identification of hydrogeochemical properties of the groundwater is indispensable for sustainable utilization of groundwater sources. In this study, the spatio-seasonal hydrogeochemical characteristics of groundwater in the unconfined aquifer of the Red River Delta have been investigated by systematically applying self-organizing maps (SOM) and Gibbs diagrams. The groundwater chemistry dataset used in the analysis is composed of eight major dissolved ions (i.e., Ca2+, Mg2+, Na+, K+, HCO 3 − , Cl−, SO 4 2 − , and CO 3 2 − ) and total dissolved solids that are collected from 47 groundwater monitoring wells within the study area during the dry and rainy seasons. The SOM application classified the hydrogeochemical data into five clusters, which revealed three basic representative water types: high salinity (one cluster), low salinity (two clusters), and freshwater (two clusters). The spatial distribution of clusters and water types were identified. In particular, the low-salinity type was found not only in the downstream area but also in the northeastern parts of the upstream and middle-stream areas, where the groundwater was mainly classified into one specific cluster, in which agricultural activities were considered to influence groundwater chemistry. Cluster changes from the dry to rainy seasons were detected in approximately one-fifth of the observations wells. Dilution by surface water may significantly affect the chemical characteristics of the unconfined aquifer during the rainy season. Based on Gibbs diagrams, rock weathering was found to be the main process in the evolution of chemical composition of freshwater type, whereas the chemical structure of the low- and high-salinity types was primarily controlled by saltwater intrusion or anthropogenic activities.

Summary The Red River Delta (RRD) is the second largest delta in Vietnam, and its local communities depend on groundwater sources for water supply. A clear understanding of the groundwater hydrogeochemical properties, particularly their changes from the dry to rainy seasons and spatial characteristics, is invaluable and indispensable for the management and protection of this important water resource. In this study, self-organizing maps was systematically applied for the first time to investigate the seasonal and spatial hydrogeochemical characteristics of groundwater in the Pleistocene confined aquifer of the RRD. The hydrogeochemical characteristics clustered by SOM were further examined using the Gibbs Diagrams. The groundwater chemistry dataset used in the analysis comprised eight major dissolved ions (i.e., Ca 2+ , Mg 2+ , Na + , K + , HCO 3 − , Cl − , SO 4 2− , and CO 3 2− ) and total dissolved solids that were collected from 52 groundwater monitoring wells within the study area during the dry and rainy seasons. Based on the results, the hydrogeochemical groundwater data of the confined aquifer monitoring wells for the delta were classified into 8 clusters, which revealed three basic representative water types: high salinity (2 clusters), low salinity (3 clusters), and freshwater (3 clusters). The high-salinity types were located in the middle-stream and coastal areas of the RRD, while the low-salinity types were observed near the western and northeastern boundaries of the delta. Cluster changes from the dry to rainy seasons were detected in approximately one-third of the observation wells. The increase in groundwater recharge during the rainy season is the main reason for these changes. Based on Gibbs diagrams, the source of soluble ions in the groundwater of the freshwater types was found to be the weathering of rock-forming minerals, while evaporation and marine activities (leaching from salty paleowater and salt water intrusion) were found to be the main factors affecting the chemistry of the groundwater characterized by the low- and high- salinity types, respectively.

In Hanoi, Vietnam, the people heavily depend on groundwater resources for both domestic and industrial uses due to the seriously polluted problems occurred in most of the river streams system. Considering the social dimension in the context of sustainable development is a key issue in groundwater resources management. The main object of this study is to assess the social sustainability of groundwater resources in Hanoi by applying a simple Analytical Hierarchy Process (AHP) approach. By applying the simple AHP, the most important task is to comprehensively study the current social situation and actual problems to define the appropriate foremost components contributing to the sustainability goal. In this study, we successfully not only select the appropriate list of three main social sustainability aspects including the quantity, quality and management aspects and the twelve core social sustainability indicators but also appropriately assessing the sustainability of the groundwater resources from the social point of view. By gathering the data from trusted sources, the groundwater quantity, quality, and management aspects are socially assessed at a good level of 0.65, a good level of 0.61 and a slightly acceptable level of 0.46, respectively. The composite social sustainability index, S, is assessed at a strongly acceptable level of 0.57, indicating that Hanoi’s groundwater resource is socially acceptable. The results of SSA are not only sensitive to data availability but also the definition of the indicators. The linear relationships do not reflect the actual situation well and the non-linear ones could be used to replace these sustainability scales of the actual values. The social sustainability indices are evaluated at the moderately high values, improbably reflecting the current problems in the target area. The study then points out the main research gaps and suggests the ways to improving social sustainability assessment for the better groundwater resource development.

In the Red River Delta, situated in the northern part of Vietnam, nearly its entire population depends solely on groundwater for daily water consumptions. For this reason, groundwater quality assessments must be carefully carried out using hydrogeochemical properties, to ensure effective groundwater resource planning for the Delta’s present and future groundwater use. In this study, the spatial and seasonal changes in the hydrogeochemical characteristics of groundwater in the two main aquifers of the RRD were investigated by analyzing the physicochemical data obtained in 2011 from 31 conjunctive wells in the Delta’s Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA) using the Piper diagram and the Gibbs diagram. Results of the data analysis show that the groundwater in both aquifers in the upstream area of the delta is dominated by the [Ca 2+ –HCO 3 − ] water-type, while the [Na + –Cl − ] dominates along the middle-stream and downstream areas. Seasonal changes in the hydrogeochemical facies in both aquifers, comparing the results for the dry and the rainy seasons, were detected in about one third of the sampling wells, which were mainly located at the upstream portion of the Delta. The hydrogeochemical facies of HUA were different from that of PCA by about 45% of the sampling wells in both the dry and the rainy seasons, which were found mostly in the upstream and middle-stream areas.

Groundwater from the Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA) is the major source of drinking and domestic water in Hanoi, Vietnam. A clear understanding of the groundwater hydrogeochemical properties, particularly their changes during the dry and rainy seasons, is invaluable for the management and protection of this important water resource. In this study, the changes in the hydrogeochemical properties of groundwater during the dry and rainy seasons were investigated by analyzing the major ions (Ca2+, Mg2+, Na+, K+, HCO3 −, SO4 2−, Cl−) that were recently obtained in 2011 from 13 conjunctive sampling wells for HUA and PCA in Hanoi. The hydrogeochemical assessment was carried out using the Piper and Gibbs diagrams. Based on the results, at least 30 % of the sampling wells in both aquifers exhibited changes in the hydrogeochemical facies during the dry and rainy seasons. Most of the changes occurred for the cation-type facies, while the anion type remained unchanged. Moreover, the hydrogeochemical facies of HUA was found to be different from that of PCA by approximately 50 % of the sampling wells for both the dry and rainy seasons. In addition, the Gibbs diagram showed apparent differences in the weight ratios Cl/(Cl + HCO3) between PCA and HUA. The results revealed that rock weathering is the main process involved in the evolution of chemical composition of groundwater, but agricultural activities and salty paleowater are the other important factors that affect the groundwater chemistry in some parts of the study area.

The predictions made using rainfall-runoff models are inherently uncertain and it is important to recognize and account for this uncertainty, especially in urban watersheds due to the high flood risk in these areas. Recent studies on hydrological model uncertainty mostly refer to the identification of model parameter uncertainty. However, such studies are somewhat limited using the bootstrap approach, a nonparametric method which makes less prior assumptions on the model structure and thus is more flexible. Hence, a residual-based bootstrap approach associated with the SCE-UA global optimization algorithm is demonstrated in this study for the analysis of calibrated parameter uncertainty and its subsequent effect on the model simulation of an urban-specific rainfall-runoff model, urban storage function (USF) model, under two different data scenarios of individual event-based and whole data-based scenarios. Initially, the parameter uncertainty was expressed by estimating the confidence interval (CI) of the USF model parameters obtained from bootstrapping and then the parameters from the highest to the lowest uncertainties were derived by utilizing two newly proposed parameter uncertainty indices which can make the best use of CI. Moreover, investigations on the effect of calibrated parameter uncertainty on model simulations revealed that the model was able to bracket most of the observations within the prediction range of considered scenarios. This further indicates that the residual-based bootstrap approach along with the SCE-UA method reasonably well predicted the uncertainty range of the USF model. For a better understanding of simulation uncertainty, we defined and demonstrated two model simulation uncertainty indices and these indices could be useful in future studies to analyze the simulation uncertainty of different rainfall-runoff models in the watersheds worldwide.

A groundwater-monitoring network has been in operation in the Red River Delta, Vietnam, since 1995. Trends in groundwater level (1995–2009) in 57 wells in the Holocene unconfined aquifer and 63 wells in the Pleistocene confined aquifer were determined by applying the non-parametric Mann-Kendall trend test and Sen’s slope estimator. At each well, 17 time series (e.g. annual, seasonal, monthly), computed from the original data, were analyzed. Analysis of the annual groundwater-level means revealed that 35 % of the wells in the unconfined aquifer showed downward trends, while about 21 % showed upward trends. On the other hand, confined-aquifer groundwater levels experienced downward trends in almost all locations. Spatial distributions of trends indicated that the strongly declining trends (>0.3 m/year) were mainly found in urban areas around Hanoi where there is intensive abstraction of groundwater. Although the trend results for most of the 17 time series at a given well were quite similar, different trend patterns were detected in several. The findings reflect unsustainable groundwater development and the importance of maintaining groundwater monitoring and a database in the Delta, particularly in urban areas.

Already today, the functionality of many sewer and storm water systems are not up to the required standards and consequently flooding problems are experienced in case of heavy storms. System upgrades are required, which are however complicated by the expected future increase in short-term rainfall intensities as a result of climate change. In this case study, focusing on the town of Arvika, Sweden, this issue is investigated in three main steps. In the first, extreme value analyses of 30-min rainfall from an ensemble of climate projections are carried out to estimate the future increase and generate a future design storm. In the second, the existing system’s response to both today’s and future design storms are simulated by a coarse sewer model setup (MOUSE) and a detailed coupled surface-sewer model setup (TSR). In the third and final step, system upgrades are designed and evaluated by both models. The results indicate an increase by 10–30 % of today’s short-term rainfall extremes by the end of the century. Upgrading the system to achieve a satisfactory performance for the future design storm would cost approximately twice as much as an upgrade based on today’s design storm.

The recent advances in GIS technology as well as data availability open up new possibilities concerning urban storm runoff modeling. In this paper, a vector-based distributed storm event runoff model – the Tokyo Storm Runoff (TSR) model – is developed and tested for urban runoff analysis using two historical storm events. The set-up of this model is based on urban landscape GIS delineation that faithfully describes the complicated urban land use features in detail. The flow between single spatial elements is based on established hydraulic and hydrological models with equations that describe all aspects of storm runoff generation in an urban environment. The model was set up and evaluated for the small urban lower Ekota catchment in Tokyo Metropolis, Japan. No calibration or tuning was performed, but the general model formulation was used with standard parameter values obtained from the literature. The runoff response to two storm events were simulated; one minor event resulting only in a small-scale flood wave and one major event which inundated parts of the catchment. For both events, the simulated water levels closely reproduced the observed ones. For the major event, also the reported inundation area was well described by the model. It was also demonstrated how the model can be used to evaluate the flow conditions in specific components of the urban hydrological system, which facilitates e.g. evaluation of flood-preventive measures.

Predictions in Ungauged Basins (PUB) mainly focus on surface water, but there are much higher prediction uncertainties inherent in groundwater. Hanoi depends entirely on groundwater for its domestic water supply. However, the characteristics of the entire Hanoi aquifer system remain poorly understood due to the lack of available data. Recently, we were nominated to construct a hydrogeological database. Using the valuable data contained in this database, this paper comprehensively analyzed the best number of 240 boreholes including well logs and their hydrogeological parameters obtained from pumping tests for the first time in order to identify the entire Hanoi aquifer system and characterize the hydrogeological conditions for potential groundwater resources. Great efforts have been made to establish and analyze the hydrogeological maps, cross sections and the isopach maps of main aquifers’ thickness and transmissibility. As for the results, we found that groundwater mainly exists in the topmost Holocene unconfined aquifer and the shallow Pleistocene confined aquifer (PCA), while cleft and karst water exists in the Neogene water bearing layer and the Mesozoic fractured zones. These aquifers are adequately, quantitatively characterized and evaluated from the viewpoint of potential groundwater resources. We found the PCA serving as the highest groundwater potential and the most important aquifer for the water supply. The findings are indispensable for further groundwater analyses contributing to ensuring the sustainable groundwater development not only in Hanoi but also in poorly gauged or ungauged neighboring basins. Copyright © 2012 John Wiley & Sons, Ltd.

The Red River Delta is one of two biggest deltas in Vietnam. People living in the delta depend entirely on groundwater for their domestic water. However, the aquifer system in the whole Red River Delta remains poorly understood due to the lack of available data. Recently, we were nominated to construct a hydrogeological database. Using these valuable data contained in this database, this paper comprehensively analyzed the best number of 778 boreholes including well logs and their hydrogeological parameters obtained from pumping tests for the first time in order to identify the entire aquifer system and characterize hydrogeological conditions in the whole delta for potential groundwater resources. Great efforts have been made to establish and analyze hydrogeological maps, cross sections, and contour maps of main aquifers’ thickness and transmissivity. As for the results, we found that groundwater mainly exists in Quaternary unconsolidated sediments as porous water forming the topmost Holocene unconfined aquifer (HUA) and the shallow Pleistocene confined aquifer (PCA) sandwiching the Holocene-Pleistocene aquitard (HPA), while cleft and karst water exist in consolidated Neogene formations and Mesozoic rocks constituting the Neogene water bearing layer (NWL) and Mesozoic fractured zones (MFZ), respectively. PCA is almost entirely distributed over the delta. It serves as the highest groundwater potential and the most important aquifer for water supply. HUA is also widely distributed about 88% over the delta and has a high groundwater potential. NWL and MFZ, placed below PCA but exposed on the surface outside the delta, are minor sources for local domestic water supply only. These findings are indispensable for further groundwater analyses needed to ensure the sustainable groundwater development for the high-security water requirements in the delta, but have never been completed sufficiently before due to the unavailability of large-scale basic data sets.

Small hillside reservoirs are fundamental for the sustainability of the water resources in the semi-arid region of Tunisia, where the government has constructed small dams since 1990. However, flash floods and severe erosion are jeopardizing the life of those small hydraulic structures prompting an assessment of the vulnerability of semi-arid catchments to erosion. In this study, we investigated the degree of erosion in 23 catchments by considering six variables related to erosion: the specific sediment yield, the hypsometric integral, the topographic index, the rainfall-related attribute as well as lithological and vegetation cover. More importance was assigned to the hypsometric integral and how it controls erosion vulnerability. The Self-Organizing Map of Kohonen, a robust clustering method, was implemented to analyze the patterns of the six variables. The results revealed four groups of catchments with different vulnerabilities to erosion. In addition, there is a global trend of increasing erosion risk from the Southwest to the Northeast of the semi-arid region of Tunisia.