Siltation

About: Siltation is a research topic. Over the lifetime, 1420 publications have been published within this topic receiving 20983 citations.

Influence of land use changes on spatial erosion pattern, a time series analysis using RUSLE and GIS: the cases of Ambuliyar sub-basin, India

Abstract: Soil erosion and its impact on the land and surface water resources are posing both ecological and socioeconomic threats around the world. In South India, tank systems are quite ancient, supporting rural livelihood including their agricultural needs. But, in recent decades they have lost their significance. The aggravated catchment erosion and resultant siltation have significantly reduced their storage capacity and thereby their functionality. Ambuliyar sub-basin, encompassing 809 irrigation tanks, has once satisfied multifunctional needs of people but now becomes degraded due to siltation. Though desilting of tanks and feeder channels is practiced, the tanks often get silted owing to aggravate soil erosion. Hence, to sustain their life span, it is essential to minimize the erosion in the catchment. Thus, the present study intends to estimate the rate of erosion, analyze their spatial variation through a time series analysis, and ascertain the causative factor. Accordingly, the annual soil loss estimated using Revised Universal Soil Loss Equation method has shown an increase in the rate of erosion from 4084.40 (1996) to 4922.47 t ha−1 y−1 (2016). However, spatially, a non-uniform pattern is inferred, and hence based on the variations, the sub-basin is divided into five zones. In zones I, II, and V, there is an increase in erosion, and in zones III and IV, a decrease is witnessed. Variations studied in conjunction with RUSLE parameters reveal that the improper land use practice has modified the erosion rate and pattern. Further, it is presumed that the silted watercourses might have increased the overland flow, which in turn increased the erosion. Remedial measures such as afforestation, promotion of coconut plantation, and reduction in overland flow by desilting tanks are suggested; thereby, the surface and groundwater resources will be enhanced and in turn the agricultural productivity.

Relative Sea Level Changes and Worsening Floods in the Western Pampanga Delta: Causes and Some Possible Mitigation Measures

Abstract: Despite declining rainfall, flooding continues to worsen around the northern end of Manila Bay. In Pampanga, flooding is enhanced by siltation of streams by sediments from the 1991 Mt. Pinatubo eruption, but the entire region has always been flood-prone, and Bulacan and Metro Manila, far from Pinatubo, also suffer worsening floods. Urbanization and deforestation are blamed, but have less impact than local sea level rise. Global warming causes the ocean surface to rise only 2 mm/yr; localized subsidence of the region from both natural and anthropogenic causes is an order of magnitude faster. Movements associated with faulting and the Pinatubo and Taal volcanoes probably are less important than the compaction of deltaic sediments under their own accumulating weights. All natural causes of subsidence are dwarfed by the contribution from excessive groundwater withdrawal, which greatly facilitates natural sediment dewatering and compaction. Several centimeters per year of documented subsidence at well sites have been corroborated by recent resurveys of elevation benchmarks established in the 1950s. In the short-term, flooding can be ameliorated by restoring original channel widths and by modifying current aquaculture practices. In the longer term, reforestation should also help by increasing infiltration and decreasing erosion and siltation. Flooding will inexorably continue in the coming century, however, both from natural compaction of delta sediments and from global sea level rise. Subsidence will continue to accelerate if the use of groundwater by the growing population is not regulated and reduced.

River sediment supply, sedimentation and transport of the highly turbid sediment plume in Malindi Bay, Kenya

Abstract: The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast. The current velocities, tidal elevation, salinity and suspended sediment concentrations (TSSC) were measured in stations located within the bay using Aanderaa Recording Current Meter (RCM-9), Turbidity Sensor mounted on RCM-9, Divers Gauges and Aanderaa Temperature-Salinity Meter. The study established that Malindi Bay receives a high terrigenous sediment load amounting to 5.7 × 106 ton·yr−1. The river freshwater supply into the bay is highly variable ranging from 7 to 680 m3·s−1. The high flows that are > 150 m3·s−1 occurred in May during the South East Monsoon (SEM). Relatively low peak flows occurred in November during the North East Monsoon (NEM) but these were usually <70 m3·s−1. The discharge of highly turbidity river water into the bay in April and May occurs in a period of high intensity SEM winds that generate strong north flowing current that transports the river sediment plume northward. However, during the NEM, the river supply of turbid water is relatively low occurring in a period of relatively low intensity NEM winds that result in relatively weaker south flowing current that transports the sediment plume southward. The mechanism of advection of the sediment plume north or south of the estuary is mainly thought to be due to the Ekman transport generated by the onshore monsoon winds. Limited movement of the river sediment plume southward towards Ras Vasco Da Gama during NEM has ensured that the coral reef ecosystem in the northern parts of Malindi Marine National Park has not been completely destroyed by the influx of terrigenous sediments. However, to the north there is no coral reef ecosystem. The high sediment discharge into Malindi Bay can be attributed to land use change in the Athi-Sabaki River Basin in addition to rapid population increase which has led to clearance of forests to open land for agriculture, livestock grazing and settlement. The problems of heavy siltation in the bay can be addressed by implementing effective soil conservation programmes in the Athi-Sabaki Basin. However, the soil conservation programmes in the basin are yet to succeed due to widespread poverty among the inhabitants and the complications brought about by climate change.

Assessment of soil erosion rate and hotspot areas using RUSLE and multi-criteria evaluation technique at Jedeb watershed, Upper Blue Nile, Amhara Region, Ethiopia

Abstract: Soil erosion is a difficult forceful practice by which useful surface soil is removed, conveyed, and stored at a detached place causing the exposure of subsurface soil and siltation in reservoirs and natural streams. It also degraded different agricultural areas at different rates and different locations as well as created gulleys, but these degraded areas, degradation rates, and gulley locations were not well identified and quantified. Therefore; the core objective of this study is to evaluate soil erosion rate and to identify soil erosion hotspot areas as well as to identify gulley locations using Revised Universal Soil Loss Equation (RUSLE), Multi-criteria Evaluation Analysis Techniques, and Geographic Information System (GIS). Land Use/Land Cover (LU/LC) map, slope map, rainfall map, and Digital Elevation Model (DEM) were the necessary inputs used for this study. The results of this study indicated that the potential annual soil loss of the watershed ranged from 0.0 to 706.7 tons per hectare per year with an average annual soil loss rate of 27.7 tons per hectare per year. From the total area of the watershed (859.2 km2), the potential area for gully expansion is 63km2. The overall analysis indicated that 4.8% of the total watershed is highly sensitive; 54.24% is moderately sensitive; 17.69% is marginally sensitive while, 23.28% is currently not sensitive and the remaining 0.06% is a /constraint to erosion. Hence, the Areas which were categorized under highly and moderately sensitive classes needed direct mediation for better conservation planning. It is concluded that Gulley, LU/LC, Topographical wetness index, and soil types are factors that enable soil erosion from high to low, respectively. It is recommended that the concerned bodies should have to take care of the area from further soil erosion through creating awareness among the society about the sustainable use of natural resources and conservation methods.