Distribution Of Sediment Deposits Research Articles

Application of mathematical model on deposition study of pumped-storage power reservoir

Sediment deposition can cause a reduction in reservoir capacity and hydro-mechanical abrasion of pumped-storage power stations (PSPSs). To increase the operating efficiency and service life of PSPSs, sediment deposition in the process of reservoir water transfer needs to be addressed. Combined with hydrodynamics, reservoir sedimentation theory and a numerical model, a two-dimensional sediment model of the lower reservoir of Tianchi PSPS was established. Considering the characteristics of the upper and lower reservoirs of this PSPS, water and sediment exchange between the reservoirs was realised by setting source and sink terms. The process and distribution of sediment deposition were analysed over 50 years. Sediment deposition in the lower reservoir of the PSPS was found to be 0.5–1.8 km in front of the dam and triangular. The main stream of sediment-carrying flow could be moved from the right-hand channel to the sediment discharge tunnel and spillway by setting up a sediment discharge trench. The average sedimentation thickness of the reservoir during 10 years of operation was about 0.8 m with a sediment intercept weir (SIW) established, while it was more than 4.2 m in the main stream area outside the SIW. For operation of 50 years, these values were 3 m and 10 m, respectively. The SIW effectively reduced deposition near the inlet (outlet) of the PSPS, the amount of sediment passing the machine and deposition to the dam front. The results provide a reference for simulations and preventive measures of sediment deposition in PSPSs.

Phosphorus Sequestration in Sediments Along the Salinity Gradients of Chesapeake Bay Subestuaries

We used a sequential extraction technique to compare the forms and amounts of particulate phosphorus (PP) deposited in the top meter of sediment spanning salinities from 0 to 10 in three Chesapeake Bay subestuaries: the Potomac, Choptank, and Bush Rivers. Fe-bound P (i.e., citrate-bicarbonate-dithionite (CDB)-extractable P) was the most dynamic fraction of PP, dominating oligohaline (salinity <3) sediments, but declining to near zero with depth in the most saline sediments of all three subestuaries. In contrast, we previously found Fe-P dominating the sediment PP at salinities ranging 0–11 in the Patuxent subestuary. Particulate organic P was relatively constant with depth and salinity and became the dominant form of PP in the most saline sediments. Fe-P was not replaced with diagenetic authigenic carbonate fluorapatite. In all the subestuaries, Fe-P generally persisted in the oligohaline sediments to 1 m depth, where sediment ages ranged from 60 to 200 years, based on 210Pb dating. At one site, PP burial reflected changing P loads from a nearby wastewater treatment plant. About 67% of the PP discharged from the Potomac watershed at the head of tide was buried in the sediments in the upper reaches of that subestuary. The form and amount of PP buried depended on the amount of CDB-extractable Fe in the sediments and on the distribution of sediment deposition along the salinity gradient. Even though CDB targets iron oxides, the predominant form of Fe in the sediments was ferrous iron suggesting that the predominant form of PP in oligohaline sediments may be ferrous phosphate.

Numerical modeling of long term reservoir sedimentation in semi-two dimensional manner

Reservoir sedimentation reduces the benefits from the storage of fresh water. The volume and distribution of sediment deposition must be predicted for a long term reservoir operation plan. Either or both experimental and numerical modeling can be applicable for an evaluation of reservoir sedimentation. Because sedimentation occurs along entire reservoirs and throughout the reservoir life span, a one-dimensional numerical sediment transport model, GSTARS, was considered in this study. Even though the model is not a truly two or three dimensional one, the model has capability of simulating channel geometric change in a semi-two dimensional manner using the stream tube concept. In this study, the effect of the number of stream tubes on the performance of the numerical simulation was analyzed using 14 years of real reservoir sedimentation data, and reasonable results were produced with three stream tubes. The densities of the deposited sediment depend on the reservoir operation scheme, especially for clay and silt. It was found that the predicted results vary with the density, and the prediction with various density with respect to location is required for a study reach where reservoir and river regions exit together.

Evaluation of an Empirical Reservoir Shape Function to Define Sediment Distributions in Small Reservoirs

Understanding and defining the spatial distribution of sediment deposited in reservoirs is essential not only at the design stage but also during the operation. The majority of research concerns the distribution of sediment deposition in medium and large water reservoirs. Most empirical methods do not provide satisfactory results when applied to the determination of sediment deposition in small reservoirs. Small reservoir’s volumes do not exceed 5 × 106 m3 and their capacity-inflow ratio is less than 10%. Long-term silting measurements of three small reservoirs were used to evaluate the method described by Rahmanian and Banihashemi for predicting sediment distributions in small reservoirs. Rahmanian and Banihashemi stated that their model of distribution of sediment deposition in water reservoir works well for a long duration operation. In the presented study, the silting rate was used in order to determine the long duration operation. Silting rate is a quotient of volume of the sediment deposited in the reservoir and its original volume. It was stated that when the silting rate had reached 50%, the sediment deposition in the reservoir may be described by an empirical reservoir depth shape function (RDSF).

Distribution of Sediment Deposits in Small Reservoirs

ABSTRACT SEDIMENT data from 12 small agricultural reservoirs were collected for periods ranging from 6 to 16 yr. Ex-cept for one small pond-type structure, sediment trap ef-ficiencies of the reservoirs ranged from 80 to 95 percent. Sediment particle size had a predominant influence on the location of sediment deposits within the structures. Coarse sediments were concentrated at the upstream end of the reservoirs near the permanent pool elevations. Fine sediments, generally less than 8 microns, were more evenly distributed throughout the impoundments. Flow detention time was sufficiently long in all of the reser-voirs to trap all but the fine sediment particles.