Siltation

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

Morphodynamic response to human activities in the bay of ca´diz (2012-2015)

Abstract: The morphology of the Bay of C\'adiz in the southwestern Spain has been changing for the past 25 years in response to the human interventions. Since 2012, new interventions, for example the new terminal and the new navigation channel, have been planned to carry out inside the Bay. As a result of these interventions, there has been a decrease in tidal amplitudes, tidal volumes, and average flow velocities, and there is hardly any sediment transport along the bay. Recent human activities are addressed in the Bay of Cadiz, an estuary located in the south--west of Spain. The Bay of Cadiz is a highly altered embayment in which socio-economical developments and ecological interests conflict. This work studies both through observations and numerical simulations the impact of some of these modifications on the morpho--hydrodynamics of the Bay of Cadiz. The capability of the bay to transport sediment between the inner and outer bay deteriorates after the deepening of the navigation channel and the construction of the new port terminal and the new bridge. This may have an impact on the ecological status of the bay. The influence of the dredging and the new terminal are concentrated at the entrance to the central sector of the bay and close to the channel. The dredging would increase siltation in the shallower areas close to the new channel, which subsequently reduce the amount of sediment input into the basins. The bridge mostly affect the Puntales Channel and the inner bay. The most changes in the erosion/deposition patterns are found in the area with strong bottom frictions and tidal asymmetries.

Minimizing Harbor Siltation (MHS)

Abstract: This paper presents methods for minimizing harbour siltation (MHS) which comprises the contents of chapter 4 of a forthcoming PIANC WG 43 report with the above title. The methods include 3 strategies: (1) KSO: Keep the sediment out, (2) KSM: Keep the sediment moving or, (3) KSN: Keep sediment navigable. 1.0 Introduction. Maintenance dredging can be minimized by locating harbors in naturally deep water or by implementing MHS measures. MHS technologies are designed to keep sediment in its natural system (KSIS). Consistent with KSIS, Krone (1987) emphasized two basic approaches to siltation minimization: (1) KSO: Keep the sediment out of a harbor, or (2) KSM: Keep the sediment moving through the harbor. A third strategy is considered here, namely: (3) KSN: Keep harbor sediment navigable. KSO strategies focus on minimizing the flow of sediment laden waters that enter harbor basins and/or navigation channels. The KSM strategies center on maximizing harbor flow velocities to prevent sediment from settling. KSN strategies are a derivative of the navigable depth concept and play on the ability of a vessel to sail through a low density fluid mud. A distinction is made between passive, i.e., those that do not require energy nor moving parts (submerged sills, flow training structures, etc.) and active measures (movable gates, locks, flow augmentation, etc.). KSO strategies are generally best suited to relatively quiescent basins where KSM is not feasible. Conversely, KSM strategies are best suited to berths located within or along relatively swiftly flowing waters, where a small increase in flow velocity will induce a significant decrease in siltation.

The scope for a system-based approach to determine fine sediment targets for chalk streams

Abstract: Fine sediment has a critical role in river ecosystems and is essential for habitat heterogeneity, ecosystem structure and function. Expansion and intensification of specific land uses, including agriculture, have increased fine sediment inputs into river networks. The detrimental impacts of excessive fine sediment on river ecosystems have been well documented and numerous sediment targets have been proposed or adopted to assess the gap between target and current levels of fine sediment. Where sediment targets exist, these are often over-simplified and applied across a wide range of river environments irrespective of the processes of fine sediment deposition and the tolerance or sensitivity of river biota to fine sediment. Thus, targets often fail to provide a reliable basis for identifying the need for management interventions to restore ecosystem health. This review adopts a system-based approach to the impacts of fine sediment after reviewing the suitability of existing targets for guiding management in chalk stream catchments specifically. Chalk streams are groundwater-dominated systems characterised by stable hydrological, ecological and thermal regimes and thus respond differently to excessive fine sediment compared with other fluvial systems. Chalk streams are often subject to high levels of sedimentation and siltation despite their low suspended sediment loads. In this paper, we review the characteristic processes and dynamics of chalk streams and how these influence fine sediment accumulation. The impacts of excessive fine sediment on chalk stream habitats and biota and the role ecosystem engineers play in the processes of fine sediment dynamics are discussed. Finally, we discuss the application of fine sediment targets for chalk streams in relation to the implementation of both source and process-based techniques for meeting the requirement for improved ecosystem management.

Predicting of Soil Loss in Tisovec Catchment, Slovakia

Abstract: Soil erosion is a major form of land degradation and has been recognized as a severe environmental problem since late 18 th century. In Europe soil erosion affects large areas and it is estimated that about 17 % of the total land area is affected. Sediments, originated by erosion, cause silting of water basins and they also affect water quality in reservoirs because they play an important role by being the ultimate sink of pollutants. Nowadays, it should be rather a preference to predict the erosion and its control. There are a lot of mathematical models for predicting of reservoir sedimentation. The most widely accepted and utilized empirical model for prediction of water erosion hazards throughout the world is Universal soil loss equation (USLE), developed by Wischmeier and Smith, which computes the average annual soil loss as the product of six major factors whose most likely values at a particular location can be expressed numerically. This paper is focused on the soil loss calculation using the USLE in the Tisovec catchment situated in the east of Slovakia, with emphasis on the suggestion of the crop/vegetation and management factor (the C factor) calculation, which is related to the land-use and represents the ratio of soil loss from a given vegetal cover. The determination of the average annual C factor is divided into five periods for each of the main periods of the cropping cycle. In accordance with the suggested calculation the total average annual soil loss from the arable land and also soil loss from the whole watershed of the Tisovec river is determined.