Socio - technical assessment of sediment management options in tidal basins in Southwestern Bangladesh

Abstract

Uniformly raising the land inside a beel and maintaining proper drainage capacity of the river are the two mam objectives of TRM, However, it is observed that sedimentation inside the beel is nol uniform in Beel Kedana and East Beel Khuksia due to the lack of social and technical limitations in TRM operation The present practice of TRM operation is to construct a link canal to connect the beel with the river. This results in sediment deposition at the mouth of the link canal, preventing further sedimentation inside the beel Tnthis study sediment management options for uniform silt depOSItion in tidal basins have been alentified in a participatol)' approach, Three options for sediment management inside the tidal basins have been identified through FGDs and consultation with the local stakeholders, In Option-l, each beel is divided into 1hree compartments by constructing embankment around the compartment and allowing sedimentation in the compartments one after another. In Option-2, embankments are constructed along both banks of the main khals through the beel and cutting the embankment part by part gradually from upstream to downstream. TnOption-3, all existing khals are connected with the river at the same time by constructing link canals, i.e, allowing sedimentation in the whole basin al the same time, Technical feasibility of these options has been assessed by a cohesive sediment transport model using MIKE21 FM modeling system, Net deposition in East Beel Khuksia and Beel Kapalia for the three options IS evaluated. The net deposItion volume after 4years in the OptlOn-l, Option-2 and Option-3 are 3,58, 4.51 and 2.6] mlilion m' respectively in East Beel Khuksia, and 3.40, 3.43 and 2.45 million m' respectively in Beel KapaJia. Maximum deposition was observed for Option-2. The net s<"hment deposition and areal extent of deposition increase after dredging of kbals So, for uniform sediment deposition inside the tidal basin, dredging of khals Inside the heel under TRM operation is required within three to four months. It is also seen that the maximum and minimum net deposition occur for Option"2 and Option-3 respectively in both beels, Besides, net deposllion volume is higher in Easl Beel Khuksia than Beel Kapalia because EastBeeJ Khuksia is located at the downstream of the Han river, • The total costs of opemtion for TRM In East Beel Khuksia and Beel Kapalia have been estimated. The minimum cost is required for Option.2 in both beels. Stakeholder consultation VIlIS carried out to finalize the acceptable option(s) fur sediment management inside -thetidal basin. After detailed discussions and consideration of different aspects of sediment management, it is appears that Option-2 is preferred by most stakeholders in the area.