The above phase of the run-off cycle pinpoints the inflow components for the surface-as well as for the ground-water resources. It has to be appreciated that there is always a balance between the inflow factors making up water resources of a region, whether surface or ground, & the outflow components.The surface water resource of a given basin in excess of the withdrawal use is accounted for on the outflow side by one or more of the following factors:
(i)Stream outflow from the basin;
(ii)loss through evaporation;and
(iii)the influent recharge to the ground water.
Similarly, the unutilised ground-water resource of a basin is accounted for by the following outflow factors:
(i)Evapo-transpiration from the ground-water-table;
(ii)outflow to the neighbouring ground-water basin;
(iii)the effluent discharge to the streams;and
(iv)the addition to the ground-water storage.
The interrelationship between the surface-water & the ground-water resources is evident from the above analysis.The surface-water resources contribute to the ground-water recharge in various ways:
(i)by influent recharge from the streams;
(ii)by seepage from natural lakes,ponds,etc;
(iii)seepage from artificial storage reservoirs,canal systems,etc, &
(iv)return flow from irrigation. These factors presently contribute to about 25 percent of the country’s total ground-water resources.
On the other hand, the bulk of the base-flow in the rivers, which represents the sustained fair-weatherrun-off is contributed by the ground-water resources. This contribution,presently, is roughly assessed at about 25 percent of the total surface-water resources of the country.
FACTORS AFFECTING WATER RESOURCES
The water resources of a region,conceived as a dynamic phase of the hydrologic cycle, are influenced by the following three major groups of factors:
- 1.CLIMATIC FACTORS
- Rainfall : its intensity,duration & distribution.
- 2.PHYSIOGRAPHIC FACTORS
- Basic characteristics.
- Channel characteristics : carrying capacity & storage capacity.
- 3.GEOLOGICAL FACTORS
- Lithologic including composition, texture, sequenceof rock types & the thickness of rock formations.
- Structural, including chief faults & folds that interrupt the uniformity of occurence of rock types or sequence of rock types also beds, joints, fissures, cracks,etc.
- Hydrologic characteristics of the aquifers permeability, porosity, transmissivity, storability,etc
The physiographic features (including geological factors) not only influence the occurence & distribution of water resources within a region but these, particularly the orography, play a significant role in influencing rainfall & other climatic factors, such as temperature, humidity & wind. However, within a geographical location & physiographic framework, it is primarily the rainfall (its intensity, duration & distribution) & the climatic factors affecting evapo-transpiration that determine the totality of water resources in the region.