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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.

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 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.

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.

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.

本論文では，近年頻発する都市型洪水被害低減を目的に，人工的に形成された非常に複雑な都市型洪水流出過程のモデル化として，既往の土地利用情報のモデル化とは異なり，個々の建物，駐車場，道路等の実際の不浸透域を抽出できる地物データGISを活用し，さらに街区，道路，雨水・下水道管路，河道の情報を付加することにより，雨水の物理的な流出経路を忠実に表現する都市型洪水流出モデルの提案を行っている．東京都内中小河川を対象流域とし，地物データGISを用いて具体的に流域のモデル化を行い，実降雨と仮想豪雨を用いて流出解析を行った．その結果，本モデルにより河川水位を精度良く再現し，また排水不良や河川水位上昇に伴う浸水現象などを含めた洪水流出過程を詳細に表現出来ることを確認した．

The objective of this study is to improve a distributed hydrologic model using SMPT (Soil Moisture Parameter Tank) model by applying kinematic wave model to river flow routing changing time step of day to an hour. The watershed basin is divided into a grid cell of 50m. This model is composed of three structure; surfaces division, river division, and groundwater division. In surface division, evapotranspiration, infiltration, percolation, interflow, and surface outflow were computed in each cell. Kinematic wave model was applied to river flow components. Groundwater component computes the groundwater levels and the flows in the saturated zone of an unconfined aquifer, stream interactions, and groundwater seepage at the ground water surface. The model is applied to simulate water cycle in the Azuma Upper Experimental basin (1.81km2) with a time step of an hour. The model parameter is calibrated through comparison of the simulated river discharge, groundwater levels with the observed value.

Understanding the interactions between surface water and groundwater is critical for effective water management and conjunctive water use planning as these are intimately linked in the hydrologic cycle. This study is the first attempt to determine the spatio-temporal patterns of the interactions between the surface water of the Red River in Hanoi, Vietnam and the groundwater of two main adjacent aquifers, the Holocene unconfined aquifer (HUA) and Pleistocene confined aquifer (PCA). In this study, an integrated surface-groundwater model was developed by coupling two commercial modeling packages: the river flow routing model (MIKE 11) and the ground flow model (MODFLOW). As for the results, this study revealed that there was very high correlation between the river water levels and HUA groundwater levels. The correlation was found decreasing not only with the distance from the river, but also from the upstream to downstream along the river. Upper parts of the river exhibited seasonal interactions of recharge and discharge between the river and aquifer, while the lower parts of the river recharged groundwater almost throughout the year.

This study investigates the water quality of the Pasig River in Metro Manila during the construction of river improvements through channel alteration. Statistical and trend analysis of surface water have been performed using the records (20082011) of 5 water quality parameters (pH, dissolved oxygen, biochemical oxygen demand, total suspended solids and EC) at 4 observation sites along the Pasig River. The trend analyses were performed using a moving average approach and nonparametric Spearman’s rho technique. The results indicate that most of the water quality parameters do not show significant trend; except for BOD and EC where these were found to significantly increasing in some of the observation sites. TSS was significantly decreasing in one site. Apart from these analyses, 14 other water quality parameters, collected annually, were assessed by comparing the values with the Philippine water quality standards. The findings of this study provide useful references for the monitoring of river water quality in Metro Manila.

Monitoring and interpreting changes in groundwater levels are essential for groundwater management. However, a fairly wide groundwater monitoring network over the Red River Delta, Vietnam was not set up until 1995. This paper investigated trends and their slopes in groundwater level series (19952009) in 63 observation wells for confined aquifer by the non-parametric Mann-Kendall trend test and Sen’s slope estimator. The analyses revealed that groundwater levels experienced significant downward trends almost all wells and time series. Spatial distribution of different trend slope was clarified over the delta in which central and coastal areas showed more serious downward trend slopes than other areas. Trend results for 18 different time series (e.g. monthly, seasonal, annual means and so on) were quite similar regardless to time series to be studied. While annual cycle in groundwater levels were strongly associated with those in rainfall and river water levels, long-term downward trends could result from increasing groundwater withdrawal.

Using the longest records (1995–2009) at a dense network of 21 observation wells available for Holocene unconfined aquifer (HUA) in Hanoi, this paper explored trends and their slopes in groundwater levels by utilizing the non-parametric Mann-Kendall trend test and Sen's slope estimator. At each well, 18 time series encompassing important groundwater level components (e.g. monthly, seasonal, annual means and so on) were analyzed to provide insights into the trends. This study highlighted that nonparametric approach is particularly suited to hydrological series in general and to groundwater level series in particular. Analyses for monthly data revealed that 12 out of 21 wells showed downward trends, while 4 wells showed upward trends. The spatial patterns of different trend slopes were also identified over HUA area. Although the trend results for other time series at a given well were quite similar, different trend patterns were detected in several time series. The findings provide useful references to sustainable groundwater development in Hanoi.

Environmental monitoring data for planning, implementing and evaluating the Total Maximum Daily Loads (TMDL) management system have been measured at about 8-day intervals in a number of rivers in Korea since 2004. In the present study, water quality parameters such as Suspended Solids (SS), Biochemical Oxygen Demand (BOD), Dissolved Oxygen (DO), Total Nitrogen (TN), and Total Phosphorus (TP) and the corresponding runoff were collected from six stations in the Yeongsan River basin for six years and transformed into monthly mean values. With the primary objective to understand spatiotemporal characteristics of the data, a methodologically systematic application of a Self-Organizing Map (SOM) was made. The SOM application classified the environmental monitoring data into nine clusters showing exclusively distinguishable patterns. Data frequency at each station on a monthly basis identified the spatiotemporal distribution for the first time in the study area. Consequently, the SOM application provided useful information that the sub-basin containing a metropolitan city is associated with deteriorating water quality and should be monitored and managed carefully during spring and summer for water quality improvement in the river basin.

Prediction of water level in small rivers is great interest for flood control in an urban area located in the river mouth. The tidal river water level is affected by not only flood discharge but also tide, atmospheric pressure, wind direction and speed. We propose a method of estimating river water level considering these factors using an artificial neural network model for the Kanda River located in the center of Tokyo. The effects by those factors are quantitatively investigated. As for the effects by the atmospheric pressure, river water level rises about 7cm per 5hPa increase of the pressure regardless of river discharge under the conditions of 1m/s wind speed and north wind direction. The accurate rating curve for the tidal river is finally obtained.