Kengo Sunada

The Governance of the Tonle Sap Lake, Cambodia: Integration of Local, National and International Levels

The Tonle Sap water-related crisis mainly concerns governance, and at both the local and cross-boundary levels the crisis requires a more integrated and comprehensive solution than is the case at present. This paper addresses the institutional challenges of this basin from three levels: international collaborative facilitation and resource mobilization toward sustainable development of the Mekong region; national and local institutional matters; and participatory issues. The results show that new governance principles such as a holistic institutional approach and upstream–downstream relationship, transparency and accountability, public participation and decentralization, gender and equity, and separation of incompatible administrative functions, etc., are much needed in the Mekong and Tonle Sap Basins. The governance should have a greater emphasis on broader policy and planning, and more strategic approaches and attention to equity, sustainability and poverty alleviation.

Population growth and natural-resources pressures in the Mekong River Basin.

Abstract The Mekong River Basin possesses the regions largest potential water source and related resources, which support ongoing economic development and basin community livelihoods. It is currently witnessing a major demographic transition that is creating both opportunities and challenges. An analysis of the complex relationship between demographic changes and impacts on the natural-resource base confirms that resource exploitation is occurring not only to meet growing domestic needs but also for other vested interests. Population, together with other major drivers, such as institutions, markets, and technology, will have a very strong bearing on the way in which the rich resources of the Mekong River Basin are developed and distributed in the present and future. The Mekong River Basins rich resources, and the benefits derived from them, are unevenly distributed both in time and geographically. Moreover, since the causes and impacts do not respect political boundaries, the Mekong countries need to jointly develop alternative management strategies to meet projected demands within the sustainable capacity of the Mekong River Basin natural-resource base.

Scenario-based Impact Assessment of Land Use/Cover and Climate Changes on Water Resources and Demand: A Case Study in the Srepok River Basin, Vietnam—Cambodia

This study investigates an interdisciplinary scenario analysis to assess the potential impacts of climate, land use/cover and population changes on future water availability and demand in the Srepok River basin, a trans-boundary basin. Based on the output from a high-resolution Regional Climate Model (ECHAM 4, Scenarios A2 and B2) developed by the Southeast Asia—System for Analysis, Research and Training (SEA-START) Regional Center, future rainfall was downscaled to the study area and bias correction was carried out to generate the daily rainfall series. Land use/cover change was quantified using a GIS-based logistic regression approach and future population was projected from the historical data. These changes, individually or in combination, were then input into the calibrated hydrological model (HEC-HMS) to project future hydrological variables. The results reveal that surface runoff will be increased with increased future rainfall. Land use/cover change is found to have the largest impact on increased water demand, and thus reduced future water availability. The combined scenario shows an increasing level of water stress at both the basin and sub-basin levels, especially in the dry season.

Evaluation of the state of water resources using Modified Water Poverty Index: a case study in the Srepok River basin, Vietnam – Cambodia

In order to evaluate clearly the state of water resources in the Srepok River basin – a typical rural area in South-East Asia, a Modified Water Poverty Index (MWPI) was developed. Indicators of five components of MWPI were evaluated using the benchmark approach. The cross-correlation among indicators of each component as well as among components were checked; and the high-correlated indicators were eliminated. The calculated MWPI and its components were then mapped and analysed to three different scales (basin, sub-basin and district). From the overall MWPI score, a general conclusion was drawn on the water poverty situation in the basin. The results reveal the variation of water poverty across the basin with the overall MWPI of 64.8, indicating that the basin is in a ‘medium-low’ water-poor situation. ‘Access’ and ‘Capacity’ components are observed to be the main causes of the water problem in the basin. There is a high disparity among the five components of MWPI when spatial and temporal variation of variables is taken into account. It is recommended that the state of water resources should be assessed based on the components rather than the composite index. The differences that scales make indicate the importance of selecting an appropriate scale for water resources assessment. By using the benchmark approach, the pertinence of MWPI results are improved and the potential for wider applicability can be extended. By examining the indicators in the five components, a policy for water development and management is proposed and specific interventions recommended. This result can provide useful information for decision-makers in prioritizing investments in the water sector.

A spatial impact assessment of human-induced intervention on hydrological regimes: a case study in the upper Srepok River basin, Central Highlands of Vietnam

The objective of this study is to assess the impact of human activity on hydrological regimes in the upper Srepok River basin, Central Highlands of Vietnam. For this purpose, specific flow and water demand for each sub-basin were first estimated and then input into the calibrated river basin management model (MIKE Basin) to generate flow data. Future land use/cover was predicted using a geographic information system (GIS)-based logistic regression approach and the population projected from historical data. The hydrologic impact of human intervention was evaluated using the indicators of hydrologic alterations method and the range of variability approach under various developed scenarios. The results show that the overall hydrologic alteration (HA) values are classified as being moderate at all reaches; they generally increase from the upstream to the downstream reaches. Flow regimes have been altered along the river under the accumulated impacts of the operations of cascade dams. However, the impacts of land-use/cover change and population growth have been found to be greater at most of the reaches. The combined scenario shows that the HA of the Srepok 3 dam downstream reach is highest (75.7%), followed by the downstream reaches of Srepok 4 (65.8%) and Buon Koup dams (43.7%). Low flow, extreme flow, and frequency and rate of change are found to be the most alterative indicators. When environmental flow is considered, the HA of all reaches are reduced, and low and extreme flows are the most reductive indicators. It has been suggested that the trade-off between instream and offstream objectives should be considered in water allocation. The results of this study would be greatly important for future understanding of the human impact on hydrological regimes.

Stock assessment and fishery management of Henicorhynchus spp., Cyclocheilichthys enoplos and Channa micropeltes in Tonle Sap Great Lake, Cambodia

ABSTRACT Tonle Sap Great Lake, in the lower Mekong River basin, contributes 60% of Cambodias inland fisheries catch. There are four types of fisheries, including the middle-scale fishery. The major species comprising the middle-scale fishery are Henicorhynchus spp. (16%), a small-bodied fish caught mainly with small-mesh nets, and Cyclocheilichthys enoplos (13%), and Channa micropeltes (7%) which are caught with a variety of gear. Here we apply the Schaefer surplus production model to the middle-scale fisheries using monitoring data collected between 1995 and 1999. Model simulations determined that the maximum sustainable yield (FMSY) for Henicorhynchus spp., was obtained with the use of 47,206 gillnets (mesh size <50 mm) and 4269 and 1605 fishing boats for C. enoplos and C. microplestes, respectively. Over 1995–1999, there was a strong trend of increase in fishing effort and decrease of catch-per-unit-effort in the waters of Pursat, Siem Riep and Kampong Chnnang provinces. These provinces have large population centres located close to the fishing grounds; fishing in these areas should be more strictly regulated.

Managing transboundary rivers: The case of the Mekong river basin

Abstract During the last decade, leaders of the Mekong Countries have found it mutually advantageous to open up the Mekong Sub‐Region (MR) for development and trade, which promises some degree of political stability and regional security. Within the present political, cultural, and economic dynamics, the Mekong River Basin (MRB) ‐ one of the major international river basins in MR ‐ is a powerful catalyst for regional cooperation that facilitates sustainable development and regional stability; if, that is, the effective management intervention is in place to make sure that the benefits and costs of river basin development are spread equitably and peacefully. Nonetheless, there are numerous stumbling blocks in achieving integrated and balanced MRB management, such as limited success in real basin wide planning, implementation and monitoring and a poor knowledge base for supporting informed decision making and, finally, political impediments. A workable and truly regional cooperative mechanism for integrated management of the MRB is yet to be developed, regardless of the existence of numerous regional institutions and organizations. The present paper proposes new schemes with (re)designing principles and performance determinants for a regional cooperative mechanism.

Trends of fish resources in the Tonle Sap basin ‐ their correlation with the hydrological conditions of the Mekong river

Abstract By using a simple ecosystem model, the study grasps the relationship between the change in inundated areas (water level and flood extends) and the level of fish production in the Tonle Sap Basin (TSB). The model produces the fish production trends that can reflect the changes in key parameters such as flood extent and relative fish area density. The results show the continued dominance of the opportunist/white migratory species in the TSBs fish composition. It reconfirms the hydrological and biological linkages between the TSB and the Mekong River that require a cross‐sectoral and cross‐boundary integrated planning and development.

Numerical Approach for the Effect of the Topography about Torrential Rain in the Tokai Aria, 2000

In this study, we investigate the effect of the topography about torrential rain in several areas. In this research, several numerical simulation was made by using Nonhydrostatic Model that Numerical Prediction Division and Meteorological Research Institute have developed. We chose three areas which are Tokai area, Kanto area and the area of north part of the Lake Biwa. Comparison among the effect of above mentioned three topographies on the atmospheric circumstance of torrential rain in the Tokai area was investigated by numerical simulation.

ANALYSIS ON THE PROCESS OF WASHLOAD TRANSPORT ON THE HINUMA RIVER

The authors conducted a set of survey on wash load transportation at the two sites in the Hinuma River, during a fl ood on June 19th, 1997, and found out a decrease in wash load concentration between the upper site (46.0km) and the lower site (28.1km). A numerical simulation was carried out to investigate causes of the decrease. CIP scheme was introduced to solve the unsteady advection-diffusion equation in the model of wash load transportation model. Results of the simulation show that the advection dominated and the diffusion did not in the process of the wash load transportation, and lateral outflow of wash load, which was caused by the trapping of vegetation, was one of the causes of the decrease in wash load concentration.