Dredging

About: Dredging is a research topic. Over the lifetime, 3300 publications have been published within this topic receiving 28325 citations.

Transport of Dredged Sediments After Disposal Operational in Lake Erie

Abstract: A dredged material disposal operation was monitored on a location in Lake Erie 8 km offshore Ashtabula, Ohio, June to November, 1975. Some 200 sediment cores were collected in the periods before and after dredging and analyzed for the grain-size distribution of the sediments. Two current meters and a wave sensor moored nearby monitored the movement of the water masses. The sediments were dredged in the Ashtabula River and Harbor and discharged at a pre-designated location by a hopper dredge. A control site was established nearby. These sediments proved to be very similar to the ones from the lake bottom at the disposal site and the control site. Because of this similarity, it was extremely difficult to distinguish between the dredged material and the lake sediments without tagging the dredged material. Plotting the percentage of sand, silt and clay in several replicates collected at one site before and after disposal of dredged material allowed distinction between local and dredged sediments. Sediment transport could approximately be determined by the use of a modified computer program (SEDMOT), which calculates and plots progressive vector diagrams based on pre-assigned critical erosion and deposition velocities for specific grain sizes. The results showed that silt-sized sediments could have been transported over distances as large as 20 km. The main direction of transport was northeast and southwest, following the bottom topography. OHIO J. SCI. 81(1): 2, 1981 A dredged material disposal operation was monitored on a location 8 km offshore Ashtabula, Ohio, in Lake Erie. One of the objectives of the program was to study the movement of dredged sediments. In order to achieve this objective, the grain size population of the sediments from the Ashtabula Harbor and River, which was to be dredged, and of the lake bottom at the disposal site was analyzed. After dredged material was disposed, we again collected lake bottom sediments at the disposal site. With the aide of current meters and a wave sensor, we attempted to interpret the resulting differences in sediment distribution and to determine possible directions and distance of transportation. Many attempts have been made to determine the amount and direction of sediment transport in water environments similar to that in Lake Erie. Manuscript received 10 March 1980 and in revised form 24 July 1980 (#80-9). Three basic methods are generally used to estimate the sediment transport: 1. analyzing sediment grain-size distributions by use of moment statistics over several time intervals and estimating the direction of transport by comparing changes in the geographic distribution patterns (Pezetta 1975) 2. estimating the direction of transport by using measured water current values (McClennen and Kramer

Blocking and dredging structure for debris flow prevention

Abstract: The utility model discloses a blocking and dredging structure for debris flow prevention in the field of water conservancy and hydropower engineering. The blocking and dredging structure mainly comprises porous dams and a comb dam in a riverway. The porous dams are provided with through holes and are arranged in a classified mode, and sizes of the through holes in the porous dams gradually decrease from the upstream to the downstream. The comb dam is located at the downstream of the porous dams, and a high-position water inlet tower is arranged at an opening of a water drainage hole. The blocking and dredging structure has the advantages that as the multiple porous dams in which the through holes gradually decrease, object sources are blocked in a classified mode and are convenient to clear, the comb dam can dredge river and take away the object sources in water, and finally influences of debris flow on the water drainage hole can be further prevented. The prevention method combining blocking and dredging is adopted in the whole blocking and dredging structure, and therefore the problems that the object sources are difficult to dredge in valleys due to the object sources are abundant in the valleys, influences are severe and other problems are effectively solved; the blocking and dredging structure has the advantage that silt can stay in the valleys and other advantages.

Nitrogen fate in drainage ditches of the coastal plain after dredging.

Abstract: Drainage ditches are a key conduit of nitrogen (N) from agricultural fields to surface water. The effect of ditch dredging, a common practice to improve drainage, on the fate of N in ditch effluent is not well understood. This study evaluated the effect of dredging on N transport in drainage ditches of the Delmarva Peninsula. Sediments from two ditches draining a single field were collected (0—5 cm) to represent conditions before and after dredging. Sediments were packed in 10-m-long recirculating flumes and subjected to a three-phase experiment to assess the sediment's role as a sink or source of ammonium (NH 4 ) and nitrate (NO 3 ). Under conditions of low initial NH 4 -N and NO 3 -N concentrations in flume water, sediment from the undredged ditch released 113 times more NO 3 -N to water than did sediment from the dredged ditch. When flume water was spiked with NH 4 -N and NO 3 -N to simulate increases in N concentrations from drainage and runoff from adjacent fields, NO 3 -N in flume water increased during 48 h compared with the initial spiked concentration, while NH 4 -N decreased. These simultaneous changes were attributed to nitrification, with 23% more NO 3 -N observed in flume water with undredged ditch sediment compared with dredged ditch sediment. Replacing the N-spiked water with deionized water resulted in two times more NO 3 -N released from the undredged ditch sediment than the dredged ditch sediment. These results suggest that ditch sediments could represent significant stores ofN and that dredging could greatly affect the ditch sediment's ability to temporarily assimilate N input from field drainage.

Bottom Sediments from a Dam Reservoir as a Core in Embankments—Filtration and Stability: A Case Study

Abstract: A possibility of using bottom sediments from dam reservoirs in earth structures was considered. Sediments from the Rzeszow reservoir (Poland) were used as research material, which, according to geotechnical standards, were classified as low permeable silt with high organic content. As fine, cohesive soil with a low coefficient of permeability, the sediments can be used in sealing elements of hydraulic engineering embankments. In order to verify the suitability of the sediments, stability and filtration calculations were carried out for embankments with a sealing in the form of a core made of the sediments. It was stated that by using a core made of sediments, the volume of seepage on the downstream side during continuous or variable backwater was significantly lower in relation to an embankment without a core, and the phreatic line did not extend to the downstream slope. It is estimated that, in the case of a planned dredging in Rzeszow Reservoir, the amount of dredged sediment would exceed 1.5 million m3, and therefore, the possibility of their economic use is essential. The search for materials that could replace natural soil in earthen structures is an important issue from both the ecological and economic points of view.