Erosion and sedimentation at Putrajaya wetland

Abu Bakar, Ahmad Farid (2009) Erosion and sedimentation at Putrajaya wetland. Masters thesis, University of Malaya.

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Erosion and sedimentation process study was carried out at Putrajaya wetland area. The sheet and rill erosion was estimated using USLE approach while the observed bank erosion throughout study area was documented entirely. The sedimentation process (in term of sediment yield) was estimated and compared using USLE-SDR approach, TSS rating curve technique (for suspended sediment yield) and wetland cell reservoir sediment yield (from wetland sedimentation survey). The USLE gross erosion and specific erosion value show a relatively high variability in term of spatial and temporal characteristic together with the effect of using different grid cell size. Sensitivity analysis was performed in GIS environment using grid regression analysis extension show that for almost all analysis year, the LS factor is the most sensitive parameter in comparison to the other factors by using 20m, 30m and 40m grid cell size. Throughout 2003 to 2004, moderate to major bank erosion had been observed and documented around Putrajaya wetland area. Bank scour and mass failure had also been observed respectively. The catchment TSS yield (suspended sediment yield) using TSS rating curve show a variability of TSS yield with 2004 value recorded higher average TSS yields in comparison to 2003. The USLE-SDR catchment sediment yield estimation using Vanoni (1975) SDR equation show a slightly lower USLE sediment yield in comparison with USLE sediment yield result using USDA-SCS (1972) SDR equation. The highest average annual reservoir sediment yield was estimated at UE1 wetland cell (536 t/ha/yr) while the lowest at UW7 (9.75 t/ha/yr). Comparative analysis between three catchment sediment yield estimation method show that the catchment sediment yields estimation using both USLE-SDR (Vanoni, 1975) and USLE-SDR (USDA-SCS, 1972) approach had overestimate and underestimate the specific TSS yield and wetland reservoir sediment yield value showing that USLE-SDR Vanoni (1975) and USDA-SCS (1972) is consider a fair to poor sediment yield estimator. The linkages between wetland TSS yield, wetland reservoir sediment yield and USLE total gross erosion could be analyzed in term of sediment delivery ratio (SDR). The increasing (UW, UN, UE and UB wetland subcatchment area) and reduction (LE wetland subcatchment area) trends of SDR value toward downstream stations was observed from the result, indicate that there was an increasing amount of sediment transported (increasing transport capacity) from upstream to downstream wetland at UW, UN, UE and UB wetland subcatchment area while declining trend of SDR values in LE wetland subcatchment area implied the effectiveness of wetland filtration processes within LE’s wetland cells. In term of sediment mitigation measure, the management should consider culvert redesigned using permanent bank reinforced structure or heavy stone to provide armor protection together with effective culvert enlargement for critical and major bank erosion inlet. Wetland geotechnical monitoring or wetland slope and embankment monitoring are also needed. Rehabilitation on wetland storage capacity is needed by using the siphon dredging technique while replanting and desilting exercise for wetland cells with dead storage (almost zero storage capacity).

Item Type: Thesis (Masters)
Subjects: Q Science > Q Science (General)
Date Deposited: 31 Jul 2013 03:12
Last Modified: 31 Jul 2013 03:12

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