Jawaharlal Nehru Technological University Hyderabad B.Tech II HYDROLOGY Previous Question Paper (July/August - 2021 - R13)

The Mass Curve method, also known as the Rippl's diagram, is a graphical technique used to determine the required storage capacity of a reservoir to meet a specific demand pattern from a given streamflow record.

The procedure involves the following steps:

1. Plot the Mass Curve of Inflow, which is a cumulative plot of the total volume of water flowing into the reservoir against time (usually months or years).
2. Plot the Mass Curve of Demand on the same graph. If the demand is constant, this is a straight line with a slope equal to the rate of demand. If the demand is variable, it is a cumulative plot of the required withdrawal over time.
3. Identify the periods where the inflow mass curve falls below the demand line. These represent periods of water deficit.
4. At the beginning of a deficit period, draw a line parallel to the demand line that is tangent to the highest point on the preceding inflow mass curve.
5. The maximum vertical intercept between this tangent line and the inflow mass curve represents the required storage capacity for that specific drought period.
6. Repeat this process for all deficit periods identified. The maximum value obtained from all these intercepts is the minimum storage capacity required to ensure the demand is met throughout the entire period of record.

The storage capacity

The hydrological cycle is the continuous movement of water on, above, and below the surface of the Earth. It is a closed system driven primarily by solar energy and gravity, involving the constant circulation of water between the atmosphere, land, and oceans.

The process consists of several key components:

• Evaporation and Transpiration: Solar radiation heats water bodies, causing evaporation. Plants contribute to this through transpiration, where water is released from leaves into the atmosphere. Together, these are termed evapotranspiration.
• Condensation: As water vapor rises, it cools and condenses into clouds, forming droplets or ice crystals.
• Precipitation: When cloud particles become heavy, they fall to the Earth as rain, snow, sleet, or hail.
• Interception: Vegetation intercepts a portion of precipitation before it reaches the ground, which may then evaporate.
• Infiltration and Percolation: Water that reaches the soil surface infiltrates into the ground. Percolation refers to the downward movement of this water through soil and rock layers to replenish groundwater aquifers.
• Surface Runoff: Excess water that cannot infiltrate flows over the land surface into streams, rivers, and eventually back to the oceans.
• Storage: Water is stored temporarily in oceans, lakes, glaciers, ice caps, and soil moisture, maintaining the balance of the cycle.

A schematic representation of the cycle depicts the sun as the energy source, with arrows showing the upward movement of vapor from oceans and land, the formation of clouds, the downward movement of precipitation, and the subsequent path of runoff and infiltration returning water to the oceans, completing the cycle.