Table 2 Description of the geomorphic unit

1

Duricrust

Denudational

Constitute gravel, silt & clay of varying lithology; silt dominates.

Poor drainage facility. Induced evaporation and percolation cause thin salt incrustation. Very fine silty clay. Groundwater potential is very poor. Runoff zone.

2

Moderately Weathered Pediplain

Denudational

Moderately thick over burden of weathered material of varying lithology

The pediplain is moderately weathered and buried due to linear erosion by strong winds. The weathered thickness is approximately between 9 and 12 m. It’s the final result of the process of erosion; Floods during rainfall as the rate of flow of water is less.

3

Pediment

Denudational

Varying lithology, Rugged surfaces with thin veneer of soil cover and rocky surfaces exposed.

It covers an area of about 97 Sq.Km in western part of the study area; Mainly surrounds the hills of various types. Poor infiltration; Runoff zone

4

Buried Pediment Shallow

Denudational

Shallow over burden of weathered material of varying lithology

Weathered thickness between 6.0–9.0 m occur in the north western part of Poondi block.

5

Structural Hills

Denudational

Coarse Texture with Varying lithology

Linear to arc shaped hills showing definite trend lines and low elevated hills; Runoff zone.

6

Residual Hill

Denudational

Linear to arc shaped hills showing definite trend lines and ridges; Runoff zone.

7

Denudational Hills

Denudational

Linear to arc shaped hills showing definite trend lines and highly elevated hills; Runoff zone.

8

Ridge/ Dyke

Denudational

Fine to medium texture with Varying lithology

Intrusion of dolerite dyke as linear features (having vary length and narrow width) called dyke ridge. Act as subsurface dam to store water.

9

Inselberg

Denudational

Coarse testure with varying lithology

An Isolated hill composed of sedimentary rocks stands above the surrounding area by surviving erosion; Caused mainly due to wind abrasion and weathering. Runoff Zone

10

Channel Bar

Fluvial

Primarily comprises of unconsolidated materials of fluvial sediments such as gravel, sand and silt and of varying grain size and varying lithology.

An elevated region of sediment that has been deposited by the flow of water. When the river level rises, the landmass disappears. Sediment supply rate is more towards Poondi reservoir. Seasonal flood zone.

11

Paleao Deltaic Plain

Fluvial

Primarily comprises of unconsolidated materials of fluvial sediments such as gravels, sand, silt and clay

A fan shaped flat surfaces and many branches of streams are seen. Finally, confluences with Bay of Bengal which normally subject to periodic flooding by present river. Recharge zone

12

Shallow Alluvial Plain

Fluvial

Constitute gravel, sand, silt & clay of varying lithology of recent formation.

Formed by extensive deposition of alluvium by major river systems. This unit is normally flat/gently undulating surface. Very good recharge zone.

13

Shallow Flood Plain / Flood Plain

Fluvial

Primarily comprises of unconsolidated materials like gravels, sand and silt

This unit is mainly found along the Kosathalaiyar and its tributaries (Nagariyar and Nandhiyar) and broadly covering the middle east part of the study area. Seasonal flood zone.

14

Valley Fill

Fluvial

Unconsolidated sediments – boulders, pebbles, gravels, sand and silt

Valley fill sediments are observed in Poondi block of about 10 Sq.Km.