ustry. Estuaries provide us with a whole suite of resources, benefits, and services. Some of these can be measured in dollars and cents, others can not. Estuaries are an irreplaceable natural resource that must be managed carefully for the mutual benefit of all who enjoy and depend on them.Oceanographyically an estuary is "a semi enclosed coastal body of water having a free connection to the open sea and within which the sea water is measurably diluted with fresh water derviving from land drainage."1 The rive water which enters the estuary mixes to some extent with the salt water thereing and eventually flows out to the open sea in the upper layer. A corresponding in flow of sea water takes place below the upper layer. The inflow and the outflow are dynamically associated so that while an increase in river flow tends to reduce the salinity of the estuary water it also causes an increased inflow of sea water which tends to increase it, thus an approximate steady state prevails.Estuaries are classified into four types.(1) Vertically mixed (TYPE A)This happens in generally shallow waters where the mixture is homogeneous from the surface to the bottom at any particular place along the estuary. The salinity increases as the distance from the head to mouth increases.(2) Slightly Stratified (TYPE B)This is similar to Type A in that it too has shallow water and the salinity increases with the distance from the head to the mouth. The water is in essentially two layers with the upper layer having an outward flow and is a little less saline then the deeper inward flow layer. At each position there is a mixing layer between them.(3) Highly Stratified (TYPE C)The upper layer increases in salinity from near zero in the river at the head to a value close to that of the outside sea at the mouth. Depp water however is almost of uniform salinity from head to mouth. Again there is a net out flow in the upper layer and inflow in the deepwater. ...
