3.1.1. Nature of Inland water environment

Unit 3- Nature of Inland water environment
3.1.1. Nature of Inland water environment
Nature of lake environment
Lake basins with steep incline of bottom at the shore regions have margins which are less subject to changes. In lakes with bordering low-lying swamp, bog or marsh areas, the margin shifts with elevation.
High and low water marks
The high water marks can usually be identified by ridges of debris and of certain bottom materials. Low water marks are easily recognized from the positions of the more prominent animal an plant zones of shallow waters.
Shore dynamics
Water is restless and during calm period some form of motion varies from relatively gentle to violent. The inland lakes the principal form of water movement produces shore changes. In lakes, particularly those of glacial origin, the shore line is much regular and simplified. The modification of original shore line has been accompanied by two main processes viz, shore cutting and shore building.
The shore cutting take place by the force of waves when the crest of oncoming wave is more or less to the shore line and the final plunge of a wave lashes against the opposing land loosening a certain amount of it. If the shore is composed of glacial drift or of soft materials, it will yield to continuously bombarding of waves. However, in regions of rocky areas the shore cutting is slowed down but the erosion is facilitated by rock fragments which are picked by the waves.
On the other hand the shore building results from several processes producing additions to the original lake margins. Exposed sandy beaches form a beach building during summer by way of waves coming on to the gently sloping where depth is less than the wave depth and thereby pushing and carrying ahead some of the sand. Under favorable conditions, the end result is substantially increased breadth of beach (above water level).
Morphometry
It can be defined as the study that deals with measurement of significant morphological features of the basin of a body of water and its included water mass is known as morphometry. Many fundamental ecological relations are directly dependent upon structural relations of water it is necessary to make measurements of various morphological features. Following general and morphometric information should be generated before studying structural and functional attributes of the system.

Before taking up the morphological studies of a lake, general information regarding type, historical background, location and general physiography should be collected.

Type : The type of body of water viz, lake, pond, marsh, swamp, well, spring, stream, river, estuary, should be noted.
Location : The locality, latitude, longitude and altitude at which the study area is situated should be noted from authentic maps.
Historical background : Collect the information pertaining to geological history of the basin and surroundings of natural waters. For artificial bodies the construction or excavation details are of importance.
General physiography : Salient physiographical features related to basin, bank and catchment area of the body of water should be noted. This includes the features of bed-rock, coarse gravel, fine gravel, debris, mud, marl, peat, sand, silt, clay, marshy, swampy etc.
The following morphometric parameters are of great importance.
1. Area: The surface area of water-spread can be calculated from a shore – line map of the body of water.
2. Bathymetry: A bathymetric or contour map is one which denotes the depth at different points in the body of water.
3. Maximum length: It is the length of line connecting two most remote extremities of the body of the water.
4. Maximum effective length: It is the length of line connecting two most remote extremities of the body of water along which wind and wave actions occur without any kind of interruption. Maximum length and maximum effective length may be the same in most cases.
5. Maximum width: It is the length of straight line connecting most remote transverse extremities of a body of water.
6. Maximum effective width: It is the length of straight line connecting more remote transverse extremities of a body of water along which wind and wave actions occur without any kind of land interruption.
7. Mean width or Mean breadth ( b ) : It is equal to the area divided by maximum length ( b ) = a/l
8. Depth: It is the vertical distance between the surface and the underlying bottom.
9. Maximum depth: It is the depth measured at the deepest point.
10. Mean depth: It is calculated by dividing the volume of the body of water by its surface area
( z ) = v/a = Volume / area.
11. Outline map: Representing the outline structure of a lake in a plane surface is called outline map.
12. Topographical map: Representing various layers of lake basin on a flat surface is called topographical map.
13. Bathymetric map: Map representing the structure and lake basin is called bathymetric map. This can be derived from outline map and topographical map.
14. Relative depth (Zr): It is the ratio of maximum depth in meters to the square root of area in hectares. Zr = dm / a2 in ha
15. Shore line: Shore line may be measured on a map by using an instrument called rotometer.
Area of the surface and each depth contour is measured by a digitizer or a polar planimeter.

Last modified: Thursday, 5 January 2012, 9:20 AM