ABSTRACT
I will start by explaining briefly the difference between a weir and a dam. A weir raises the water level in a stream or river to a more or less fixed level. On the Thames, for example, there are several weirs including the one at Teddington. In the old days weirs were frequently built to divert water to a water mill or for fish breeding purposes. Very often a weir served both purposes and depending on whether the stream was navigable or not, it may or may not have had lock gates in it. A structure may also be built across a stream for the purpose of storing water. It has to be designed so as to allow a large variation in water level, the larger the variation the greater the amount of water stored. These structures are referred to as dams, the lakes so formed reservoirs.
