HYDROLOGICAL ALTERATIONS FROM WATER INFRASTRUCTURE DEVELOPMENT IN THE MEKONG FLOODPLAINS Thanh Duc Dang1, Thomas A. Cochrane1*, Mauricio E. Arias2, Pham Dang Tri Van3, Tonny de Vries1 1
Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch, New Zealand
2
Sustainability Science Program, Harvard University, Cambridge, USA
3
Department of Water Resources, College of Environment and Natural Resources, Can Tho University, Can Tho, Vietnam
*
Corresponding author:
[email protected]
Abstract The Mekong floodplains, which encompasses the region from Kratie Township in Central Cambodia to the Vietnamese East Sea, is a region of globally renown agricultural productivity and biodiversity. The construction of 135 dams across the Mekong basin and the development of delta-based flood prevention systems have caused public concern given possible threats on the stability of agricultural and ecological systems in the floodplains. Mekong dams store water upstream and regulate flow seasonality, while in situ flood prevention systems re-distribute water retention capacity in the floodplains. The main aim of this paper is to evaluate possible impacts of the recent development of both hydropower dams and flood prevention systems on hydrological regimes in the Mekong floodplains. An analysis of measured daily and hourly water level data for key stations in the Mekong floodplains from Kratie to the river mouth in Vietnam was conducted. Hydropower dam information was obtained from the hydropower database managed by the Mekong River Commission, and the MODIS satellite imagery was used to detect changes in flooding extent related to the operation of flood prevention systems in the Vietnam Mekong Delta. Results indicate that the upper part of the floodplains, the Cambodian floodplains, may buffer upstream dam impacts to the Vietnam Mekong Delta. Flood prevention up to date has had the greatest effect on the natural hydrological regime of the Mekong floodplains, evidenced by a significant increase of water level rise and fall rates in the upper delta and causing water This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/hyp.10894 This article is protected by copyright. All rights reserved.
levels in the middle delta to increase. The development of flood prevention systems has also effected spatial distribution of flooding as indicated via a time series analysis of satellite imagery. While this development leads to increase localized agricultural productivity, our historical data analysis indicates that development of one region detrimentally affects other regions within the delta, which could increase the risk of future conflicts among r, economic sectors, and the ecological value of these important floodplains.
Key words: Mekong River, floodplains, indicators of hydrological alterations, hydropower dams, flood prevention systems.
1.
Introduction
Hydrological alterations have been broadly defined as changes in the magnitude, frequency, duration and predictability of river flows caused by human activities (Poff et al., 1997; Rosenberg et al., 2000). These alternations can have subsequent impacts on riverine and floodplain systems, including changes to local agricultural productivity and fisheries. Hydrological alterations may also result in the instability of aquatic biota and riverine ecology (Townsend & Hildrew, 1994; Stanford et al., 1996; Poff et al., 1997). For example, temporal reductions in flows can influence drought stress on aquatic vegetation, invertebrates and fish (Bunn & Arthington, 2002). Additionally, flow modifications may alter the nutrient entrapment capacity of waterways, impact exotic species migration, and change the interaction between water and river banks causing geomorphologic changes (Poff et al., 1997; Bunn & Arthington, 2002). The operation of water infrastructure may disrupt the natural movement of water and may change important hydrological indicators such as water level rise and fall rates, flooding extent, and extreme (annual, seasonal and monthly) water levels. Water level rise and fall
This article is protected by copyright. All rights reserved.
