Sediment budget and source in the catchment of the River Rother, West Sussex

Abstract

The purpose of the study was to undertake a quantitative assessment of the proportions of river sediment derived from the various rock types within the catchment.b) to determine the rate of removal of sediment from the catchment.The former purpose involved the determination of the mineralogy of source rocks, soils, alluvium and sediment by X.R.D. and heavy mineral analysis. The data indicate that each source rock has a characteristic mineralogy, but that this is not sufficiently variable for a quantitative assessment of proportions of sediment from each source rock to be determined. Certain conclusions, however, are drawn from the data, including a tentative formation, by sorting on a basis of specific gravity, of heavy mineral assemblage zones in channel sediment, that are probably indicative of areas of aggradation and degradation.To determine the rate of sediment loss from the catchment, the dissolved load, the suspended load and thebed load were investigated. The dissolved load includes Ca2+ and HCO3 formed from the solution of Chalk, anderosion rates of CaCO3 have been estimated at approximately 39.8 tonnes/km. 2/year.Suspended sediment concentrations were determined for samples collected from a variety of stations during a variety of flow conditions. An estimated 2,182 tonnes of suspended sediment was lost from the catchment in 1972 , of which 1,720 tonnes was non-organic. The data indicate that the frequency and duration of storm events is a major controlling factor for suspended sediment concentration. Pates of bed load movement were determined using fluorescent sand tracers for two stretches of the Pother and a relationship between grain size, river discharge and sediment loss is presented for each. Modifications of techniques and methodology for use of fluorescent tracers are suggested and the data indicate the probability of aggradation of sizes of medium sand and larger between the two experimental stretches.