SOME ASPECTS OF THE HYDROLOGY OF THE THAMES BASIN.

Abstract

The Paper is introduced by a brief history of the earliest records of the flow of the Thames, and of the first systematic recording of the daily discharge at Teddington Weir. The surface catchment area is discussed, and reference is made to the changes that have been taking place in its character, caused by housing and other forms of development. The hydro-geology of the basin is briefly described, and an estimate is made of the true area believed to be contributing to river discharge. The methods of obtaining rainfall statistics are discussed, and the sites of the recording stations are shown on a map. Distribution of rainfall on the catchment area is shown on a map from which mean annual rainfall on the principal geological formations within each tributary was obtained and tabulated. The sites of observation wells are shown, in which the rest-water level in the chalk and oolites is regularly observed. Groundwater is defined and methods of estimating monthly and annual average discharges are described and the results are shown in a number of tables. Direct or storm run-off in relation to rainfall is examined from the data of a large number of floods and lower discharges, with special referentcoe a ntecedent rainfall conditions. The unit hydrograph is discussed and comparison is made between unit hydrographs for Teddington resulting from rainfall of various durations. Long-term averagesa re compared with thosefr om a large numbero f rivers in Great Britain, enabling mean annual losses to be deduced from a table and a graph. Floods on the Thames and tributaries, their history and frequency are referred to, and flood frequencies are shown graphically. Some high flood discharges of a number of tributaries are tabulated, the run-off per unit area given, and comparison made with run-ofaf t Teddington. Dry weather flows are discussed and their frequency for the Thames at Teddington is shown graphically. Comparison is made between dry weather discharges of the principal tributaries and of the Thames.