E-Flows in the Nam Songkhram River Basin

This report details an interdisciplinary Environmental Flows (E-Flows) assessment of the Nam Songkhram River Basin in Northeast Thailand. The study examines the critical relationship between the Mekong River mainstream and the Nam Songkhram floodplain, emphasizing how the annual 'flood pulse' sustains high aquatic biodiversity and local livelihoods. The findings highlight a transition from natural wetland habitats to simplified ecosystems dominated by agricultural land and industrial tree plantations, specifically eucalyptus. The report argues that upstream flood control infrastructure is largely futile due to the dominance of the Mekong's hydrology and recommends a holistic, multi-stakeholder approach to basin management to prevent further ecological collapse.

• The lower reaches of the Nam Songkhram River function as a productive floodplain system characterized by high aquatic biodiversity and a wide range of habitats. However, moving up the river system, annual flooding periods decrease and human disturbances increase, leading to a corresponding decline in aquatic productivity and biodiversity.
• The hydrology of the Lower Nam Songkhram River Basin (LSRB) is primarily controlled by the Mekong mainstream. This relationship is characterized by a pronounced backwater effect and occasional reverse flows, where Mekong waters flow upstream into the Nam Songkhram for 70 to 100 kilometers, typically lasting 4 to 9 days and occurring most commonly in July.
• Because the Mekong mainstream dominates the timing, duration, and extent of flooding in the LSRB, building flow control infrastructure on the Lower Nam Songkhram River or its main tributaries, such as the Nam Oon, is likely to be futile and counterproductive. Simulation models indicate that a total absence of discharge from the Nam Songkhram tributaries would only decrease the flood peak by 0.1 meters.
• The LSRB is undergoing an ecological transformation from diverse wetland habitats to a simplified ecosystem. This is driven by the wholesale removal of natural forests and their conversion into agricultural land, specifically paddy fields and industrial monocrops such as rubber and eucalyptus. Forest cover in the entire LSRB is estimated to be no more than 10-12%, and the area of seasonally flooded forest declined from 91.58 km2 in 2001 to 69.24 km2 in 2005.
• The basin supports a highly biodiverse capture fishery, with at least 188 fish species identified. The productivity of this fishery depends on the 'flood pulse' and connectivity with the Mekong, which allows for bi-directional migration. However, instream obstacles like the Nong Gaa Weir act as total physical barriers to upstream migration except during flood conditions.
• Local livelihoods are shifting from subsistence-based economies and the harvesting of non-timber forest products (NTFP) toward commercially-oriented agriculture and off-farm income. In some LSRB villages, approximately 61% of households derive their main income from off-farm sources, with remittances often being nearly three times greater than local agricultural earnings.
• The rapid expansion of eucalyptus plantations is driven by the pulp and paper industry and the tree's tolerance for flooding and fire. This expansion has led to the loss of seasonally flooded forests and created conflicts between livestock raisers and crop growers as common grazing lands are privatized and fenced off.
• The Giant Mekong Catfish (Pangasianodon gigas) utilizes specific 'din euad' (salty soil) areas in the floodplain for feeding during the rainy season. Laboratory analysis shows these areas have very high potassium and high phosphorous levels, with an Electrical Conductivity (EC) of 7.58 dS/m compared to 0.22 dS/m in nearby soils. The construction of small dams, such as the one on Huay Sing, has blocked access to these feeding grounds, causing the local fishery to virtually disappear.

APA

Blake, D. J. (n.d.). E-Flows in the Nam Songkhram River Basin. Stockholm Environment Institute. https://www.sei.org/mediamanager/documents/Publications/SEI-ResearchReport-Osbeck-EFlowsInTheNamSongkhramRiverBasin-IUCN-2011.pdf

Chicago

Blake, David J.H. E-Flows in the Nam Songkhram River Basin. Stockholm Environment Institute, n.d. https://www.sei.org/mediamanager/documents/Publications/SEI-ResearchReport-Osbeck-EFlowsInTheNamSongkhramRiverBasin-IUCN-2011.pdf.

Wikipedia

{{cite report |last1=Blake |first1=David J.H. |title=E-Flows in the Nam Songkhram River Basin |publisher=Stockholm Environment Institute |url=https://www.sei.org/mediamanager/documents/Publications/SEI-ResearchReport-Osbeck-EFlowsInTheNamSongkhramRiverBasin-IUCN-2011.pdf |access-date=17 August 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{blakendeflows, author = {Blake, David J.H.}, title = {{E-Flows in the Nam Songkhram River Basin}}, institution = {Stockholm Environment Institute}, url = {https://www.sei.org/mediamanager/documents/Publications/SEI-ResearchReport-Osbeck-EFlowsInTheNamSongkhramRiverBasin-IUCN-2011.pdf}, urldate = {2026-08-17}, note = {Indexed by Climate Insights Directory} }