JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III WATER RESOURCES ENGINEERING Previous Question Paper (August - 2022 - R16)

Infiltration is the process by which water on the ground surface enters the soil. It is the downward movement of water through the soil profile, replenishing soil moisture and contributing to groundwater recharge. The rate at which water enters the soil is known as the infiltration capacity.

Factors affecting infiltration include:

• Characteristics of the soil: Soil texture (sand vs. clay), structure, and porosity determine the size and connectivity of voids. Sandy soils have higher infiltration rates than clayey soils.
• Initial moisture content: Drier soils exhibit higher initial infiltration rates due to higher suction gradients, whereas saturated soils have minimal infiltration capacity.
• Vegetative cover: Vegetation intercepts rainfall, reduces surface runoff velocity, and improves soil structure through root systems, thereby increasing infiltration.
• Surface conditions: Compaction, crusting, or the presence of impervious surfaces (like pavement) significantly reduce infiltration.
• Rainfall intensity: If rainfall intensity exceeds the infiltration capacity, surface ponding and runoff occur.
• Temperature and fluid properties: Higher water temperatures decrease viscosity, facilitating faster movement through soil pores.

Methods for estimating evaporation from water bodies include the use of evaporation pans (e.g., Class A pan), the water budget method, the energy budget method, and the mass transfer method (aerodynamic method).

The Evaporation Pan Method is the most common empirical approach. A standard pan, such as the Class A pan, is filled with water, and the drop in water level is measured over time. The evaporation from the lake or reservoir is estimated by applying a pan coefficient:

Where E_l is the lake evaporation, E_p is the pan evaporation, and C_p is the pan coefficient (typically around 0.7 for a Class A pan). This method is simple but requires careful maintenance to account for precipitation, wind effects, and the difference in heat storage between the shallow pan and the deep water body.