High-Precision Measurements of Wetland Sediment Elevation: I. Recent Improvements to the Sedimentation-Erosion Table
Donald R. CahoonJames C. LynchPhilippe HenselRoelof BoumansBrian C. PerezBiología Aplicada del SeguraJohn W. Day
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ABSTRACT The sedimentation-erosion table (SET) developed by Boumans and Day (1993) is herein renamed the surface elevation table (SET) to better reflect the conceptual view of the processes being measured. The SET was designed for making high-resolution measurements of small-scale changes in elevation of loose, unconsolidated sediments in shallow water and mudflat habitats. The SET has undergone three major improvements to increase precision and so that it can be used to measure sediment elevation in vegetated wetlands as well as shallow water habitats. The remote-release sliding mechanism has been replaced with a single plate, collars (first 2.5 cm then 7.5 cm in length) have been attached to the plate to reduce play in the placement of the measuring pins, and the brass measuring pins have been replaced with fiberglass pins to reduce bending and consequent loss of precision. Under ideal laboratory conditions, the 95% confidence limit for individual pin measurements averaged about ± 1.4 mm (range ± 0.7 to ± 1.9 mm). These modifications have resulted in a reduction of error by about 50%.Keywords:
Sedimentation
Elevation (ballistics)
Table (database)
Abstract The Cengklik Reservoir is operated for irrigation of rice fields in 3 sub-districts in Boyolali Regency, namely Sambi, Ngemplak, and Nogosari. At the present time, the volume of the Cengklik Reservoir has decreased and resulted in dryness during the dry season. One of the main causes is due to the high sedimentation rate. This research was conducted to evaluate changes in land use that resulted in sedimentation in the Cengklik Reservoir. Erosion prediction in this study uses USLE (Universal Soil Loss Equation) analysis. The amount of sediment obtained uses the standard erosion data from USLE calculations, namely by multiplying the amount of erosion by the SDR and the area of River Basin. The potential for erosion and sedimentation used land use data for 10 years, from 2009 to 2019. Based on the research, the amount of erosion and sedimentation in the Cengklik Reservoir was fluctuated with the highest amount occurring in 2016, with erosion of 9,292 tones/ha/year and sedimentation of 4304,154 tons/year. In general, erosion and sedimentation have increased from 2009 to 2019. The classification of erosion in the Cengklik Reservoir according to this study was categorized as light erosion. The trap efficiency used in this study was calculated using formulae based on the research of Heinemann (1981) using the Brune method for small reservoirs with an area of less than 0.5 km2. In general, based on this study, the Trap Efficiency in Cengklik Reservoir was 95.254%.
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More than 10,000 reservoirs have been constructed in agricultural watersheds in the United States since the 1940s to control floods and sediments. Reservoir sedimentation records provide a unique opportunity to retrospectively study the effects of land use changes and climate variations on sediment production if the sediment chronology could be properly determined. The objectives of this study were to: (i) evaluate the applicability of four unsupported 210 Pb ( 210 Pb ex ) models for dating deposited sediments in fast‐sedimentation environments; (ii) estimate the sedimentation rates; and (iii) relate the sedimentation rates to changes in soil conservation measures, land use, and climate. Three sediment profiles were sampled at 5‐cm intervals in a flood control reservoir in the Fort Cobb Reservoir Experimental Watershed in southwestern Oklahoma. Radioactivity was measured with a γ spectrometer for radioisotopes 137 Cs and 210 Pb. Four 210 Pb ex dating models were tested. Three models (constant flux–constant sedimentation [CFCS], constant initial concentration [CIC], and constant rate of supply [CRS]), which are widely used in the lacustrine and marine environments under slow‐sedimentation conditions, were not applicable to fast‐sedimentation conditions because of considerable 210 Pb ex input with the sediment, which is assumed negligible in the models. A modified CRS model that uses 137 Cs age markers as references improved determination of the sediment chronology. The average sedimentation rates were three to five times higher during the 1957 to 1963 time period than during the 1964 to 2011 period. The significant sediment reductions coincided with the implementation of numerous conservation measures in the watershed, including check dams, terraces, changing cropping patterns, and progressive adoption of no‐till and conservation tillage systems.
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Based on the multi-sensors remote sensing data of Landsat TM acquired in 1986 and 1994, Landsat ETM+ acquired in 2000, CBERS-02 CCD acquired in 2005, and ALOS AVNIR-2 acquired in 2009, the wetlands in Fuzhou coastal zone were classified using stratified decision rules. The coastal wetlands were divided into two categories: natural wetlands and artificial wetlands, from which the natural wetlands include five classes, while the artificial wetlands include three classes. The spatial patterns and dynamic changes of coastal wetlands from1986 to 2009 were analyzed. The main changes of coastal wetlands happened during 1994 to 2005, and there were only a few changes before 1994 and after 2005. From 1986 to 2009, the total area of wetlands had decreased. The area of natural wetlands had decreased during the whole period, and was mainly transformed into aquacultures and non-wetlands area such as construction lands. The area of artificial wetlands had decreased before 2000 and increased after 2000, in which the area of aquacultures had increased very rapidly, and were mainly transformed from non- wetlands area, paddy fields and natural wetlands. The spatial pattern and dynamic change of coastal zone was jointly affected by local policies adjustment, the driving of economic interests and population increase. The temporal wetlands changes were closely related to the local policies.
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Potential erosion and sedimentation for three small stream basins near Dodoma, Tan-zania are simulated using SOILCART, a computer program recently developed to assist in the investi-gation of soil erosion problems. Using only widely available generalized data, the predicted values of soil erosion and sedimentation derived from SOILCART compare favorably to measured values which required a 2-year field investigation. Potential areas of high erosion are identified that could be amelio-rated with proper management. The potential use of SOILCART in preliminary evaluation of erosion and sedimentation problems promises useful results, especially in areas where small dams are proposed.
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Through comparative analysis of the erosion-deposition variation in the Yellow River estuary under the natural and flow/sediment regulation condition,the paper explored the influence mechanism of the Xiaolangdi project on the erosion-deposition variation.The results showed that there was a significant positive relationship between land-forming area and the flow and sediment in the Yellow River.The Xiaolangdi project regulation improved the flow and sediment condition in the Yellow River,which rapidly changed the Yellow River estuary state from erosion to deposition and the spit extended at the rate of 0.9km/a,resulting in a land-forming rate 1.34times from 2003to 2006which was higher than that under the natural flow/ sediment condition from 1977to 1989and an extending length per 0.1billion of spit 2.9times.The Xiaolangdi project should regulate the flow/sediment about 0.02t/m3 and the incoming sediment coefficient to 0.01～0.015(kg·s)/m6 in Lijin station,which was at least about 2×1010 m3 of flow,(3～4)×108 t of transported sediment and 6.34～9.52kg/m3 of sediment concentration,to drive the Yellow River estuary development in the positive direction.
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The regulation mechanism of coarse and fine sediment in Sanmenxia confluence region and in the lower Yellow River is studied as the key issue on the basis of recorded data and combining with mathematical model. The analysis and calculation show that detention of coarse sediment will result in the ratio of 0.5 to the sedimentation reduction respectively for the confluence region and the lower Yellow River, therefore, the main effect of sedimentation reduction is in the lower Yellow River. If coarse sediment concentration of entering to the lower Yellow River had been controlled between 15?% to 20?% from 1974 to 1990, there would have been the ration of sedimentation reduction of 0.65 to 0.80 and with mainly decreased coarse sediment in the lower Yellow River.
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Radiometric dating
Sedimentation
Optical dating
Varve
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This paper introduced the sediment concentration control and measurement system for sedimentation model test,which was successfully used important scientific research project in our country.This system can be used in controlling and measuring the sediment concentration and grain size analyzing,automatic measuring and alarm the water level in reservoir etc.
Sedimentation
Sediment control
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