Lake Morphology and Morphometry

The origin of a lake reflects some basic conditions of lake morphology and morphometry. These conditions change over time due to numerous factors, especially human activities and other events in the catchment area. Such interactions with lakes and reservoirs are very important because of the relationship between the area of the lake or basin, the size of the basin and the water-holding time. It is necessary to know at this time to replace all the water in the lake. In this case, limnology of any lake plays an important role. 

All kinds of human activities in the drainage basin affect the lake system. When the drainage network branches are connected, there is a deep connection between the different river channels. As a result, knowledge about water retention time is essential for pollution control and monitoring and determining the balance of nutrients. The retention period has crucial biological significance and effects on the eutrophication process.

To understand the origin and structure of lakes, it is first necessary to determine their bathymetry and different depths. Bathymetry is currently performed using echo-sounding equipment with GPS (Geographic Positioning Method) to determine the exact position of each edge.

The indicators mentioned in the chart below are used to express major measurements and morphological features:

Parameters	Symbolic Signs
Area	A
Volume	V
Maximum length	Lmax
Maximum width	Lamax
Maximum depth	Zmax
Average depth	Z
Relative depth	Zr
Perimeter	M
Index of development of margin or shoreline	DL
Development of volume	DV
Average slope	α

Bathymetry plays a major role in identifying these factors and measuring the morphometry and morphology of the lake.

Area of lake or Reservoir

There is usually a difference between the total area which includes the islands and its waters. This area can be calculated on the basis of maps or planimeters, aerial photography or global positioning satellite imagery.

Volume

The area is determined by measuring each boundary of each area. Adding these volumes by determining the area between the lands one after the other gives the lake`s volume.

Maximum length-L_max and Maximum width- La_max

The maximum length of a lake is measured using a map or aerial photograph or satellite image. The distance between two distant points of a lake along a straight line is called the maximum length. The full effective length is vital in the application of hydrographic and limnological applications. The distance between these two points is called Fetch (Von Sperling, 1999). If there is a longer Fetch, the effect of air on the surface of the lake or reservoir is useful. The maximum width refers to the maximum distance between the arrow at right angles and the full length.

Maximum Depth- Z_max

The maximum depth can be determined directly from the Bathymetric map. Maximum depth plays an important role in the calculation or future measurement of vertical circulation of lakes and reservoirs.

Average depth-Z

The average depth is obtained by measuring the depth from different places of the lake or reservoir through sampling and dividing by the number of sampling. According to Raushan (1955) the biological productivity of a lake is related to the average depth.

Relative depth-Z_r

Relative depth is expressed as a percentage. The ratio of maximum depth to average diameter of a lake is called relative depth. The higher the depth of the lake, the more stable the thermal stratification.

Perimeter-M

The term perimeter is used to measure the contour of a lake. It is determined by maps or aerial photographs and measurements. The value of the perimeter is expressed in meters.

Index of development of margin or shoreline-D_L

The level of shoreline measurement is the shoreline development index. This is the relationship between the length of the shoreline of a lake and the length of the circumference of a circle in an area equal to the lake. It measures the deviation of the size of the lake from the circular pattern.The shoreline development index is given below:

In the case of a typical circular lake, the deviation of the lake from a circle is 1.5 to 2.5 as opposed to D_L = 1.0. In case of very irregularly branched lakes, its value is 3.0 to 5.0.

Development of Volume-D_V

This indicator is used to express the type of lake basin. It indicates the ratio of the lake`s  size with an angle equal to the maximum depth of the lake and the area of the lake. The Volume Development Index (DV) is usually about three times the Z: Zmax ratio.

Average Slope- α

The average slope of the lake can be calculated by the following formula:

Timms (1993) presented the following formula for measuring the average slope-

Hutchinson (1956) described the anatomy of different types of lakes as follows:

• Circular: Volcanic lakes, especially the ancient volcanic lakes.
• Elliptical: Such lakes are formed due to the flow of air and the transfer of various elements to the round lakes. Such as glacial lakes.
• Oval: Arctic lakes are an example of such lakes.
• Long sub-rectangular: The lakes formed from glaciers in the Glacier Curve Valley. They are roughly rectangular in shape.
• Branched lakes: Such lakes are formed by siltation in submerged areas. The lake has many branches.
• Triangular lakes: The size of such lakes is very triangular.
• Irregular lakes: Such lakes are found in all the basins of the region which have formed irregular lakes.

Lake Morphology; A Showing lake and B Shoing Artificial Reservior

Shallow Lake

Shallow lake is very important limnologically and ecologically. Loffler (1982) limnologically separated shallow lakes with a small amount of sediment and shallow water lakes with a large amount of sediment or sediment due to sedimentation. Horizontal slopes of salinity are observed in many shallow saltwater lakes. The main feature of these lakes is that their vertical structure always affects the upper part of the mass of the whole body of water which is affected by wind and waves. The average depth of these lakes is 10 m or less and the bottom is flat or slightly concave.

The following common features of shallow lakes can be seen:

1. Irregular sediment storage is sometimes hampered by erosion;
2.  Horizontal zonation of different biotic and abiotic parameters is always greater than vertical zonation.
3. Absence of effective vertical and horizontal circulation and long term stratification period. Lakes are usually of the polymic type.
4. The effect of eutrophication is more in such lakes.
5. Lack of internal current rises above the submerged area as the levels decrease.
6. Significant numbers of aquatic birds are seen due to eutrophication and increased influences on bio-geochemical cycles.

Ancient deep lakes are turned into shallow lakes due to sedimentation. Such lakes are found in highlands, such as South America, Mexico, and Asia. Such a lake is also called a second stage shallow lake.

Name of Lake	Area(km2)	Average Depth(meter)	Secchi Reading (meter)	Lake Type	Chemical Characteristics	Area covered with Floating Aquatic Plants(%)
Lake George(Africa)	250	–	–	Secondary shallow lake	Freshwater	10
Lake Balaton (Hungery)	600	3.3	0.20-4.00	Secondary shallow lake	Freshwater/Alkaline	10
Lake Niriz(Iran)	1240	0.5	1.0		–	10
Lake Chand(Africa)	20900	3.4	0.08-0.8		Freshwater/Alkaline	10

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