Erodibility Potential of a Sand Dredging Site in Rivers State, Nigeria

Abstract

Dredging operations entail the removal of bed materials and associated vegetation from a river channel. It is an underwater excavation to re-establish a channel so as to improve navigation or for commercial activities [1]. The dredged materials may be deposited in uniform layers over wet land vegetation or open bay bottom [2]. In Nigeria, manual dredging by natives has been in operation since the early part of the 19th century. This according to Aroh [3] was to get sharp sand (for construction purposes) and prevent sinking of boats. Sand erosion is a gradual change that is difficult to determine from environmental agents e.g. rainfall, runoff, streams and wind solely but coupled with dredging activity, sand erosion is determinable. Sand erosion is generally a three-step process of sand particles detachment, particles transportation or particles displacement and finally deposition at a different or new location [4]. Sand itself is a material with lesser degree of cohesion and therefore is vulnerable. The susceptibility of sand surface to the vagaries of erosion defines sand erodibility.Sand physical properties, namely particle size distribution (soil texture), structure, organic matter content and permeability govern erodibility [5]. Texture is the mix proportion of sand, silt and clay.Erodibility is high for sandy soil. Sandy soils with small amounts of fine, medium or coarse particles (2.00mm and 0.02mm) are found to have high erodibility. Sand structure is the aggregation of identifiable shape and bad aggregation which enables the sand to be eroded by the detachment force of a dredger. Also, sand organic matter (SOM) being highly discouraged due to heat in sand does not bind sand particles together into sticker aggregates, thereby offering no resistance to erosion. Permeability is the measure of the rate at which water percolates through sand under a head of water and is a function of sand structure, texture and bulk density, hence a function of sand particles [4]. Because of the high percolation feature of a sandy soil, erodibility is high hence erodibility can be defined by soil partcles size distribution. Particles size distribution is very important in soil conservation, engineering and management