• First requirement – Q (discharge)
• Hydrology deals with occurrence and distribution of water over and under earth’s surface.
– Surface Water Hydrology
– Ground Water Hydrology
• Watershed, catchment area or drainage area: length of the river, size and shape of the area it affects, tributaries, lakes, reservoirs etc.
• Investigation of run-off for past few years is required for power potential studies of a HPP.
Objectives of Hydrology
• To obtain data regarding the stream flow of water that would be available,
• To predict the yearly possible flow
• To calculate the mean annual rainfall in the area under consideration from a record of the annual rainfall for a number of years, say 25 to 30
• To note the frequency of dry years
• To find maximum rainfall and flood frequency Various terms related to Hydrology
• Rainfall is also known as precipitation and can be measured by rain gauges.
• Some part of precipitation is lost due to evaporation, interception and transpiration.
• Transpiration: Plants absorbing moisture and giving it off to the atmosphere
• Stream flow = precipitation – losses
• Stream flow = surface flow + percolation to ground
• Surface flow is also known as run-off.
– shows the variation of stream flow in m3/s with time for a particular river site. The time may be hour, week, month or a year.
– The area under hydrograph gives the total volume of flow
• Flow duration curve
– shows the percentage of time during the period when the flow was equal to greater than the given flow.
– The area under FDC gives the total quantity of run-off during a period
• Mass curve
– indicates the total volume of run-off in cubic meters up to a certain time.
– the slope of the curve at any point shows the rate of flow at that time
– Used for estimating the capacity of storage reservoir
– to ensure water availability during deficient flow and thus increasing the firm capacity
– Storage also results in more energy production
– Storing water in small ponds near the power plant as the storage reservoir is away from plant
– To meet the power demand fluctuations over a short period of time e.g. 24 hours
• Primary Power: power that will be available 90 % of the time
• Secondary Power: power that will be available 75 % of the time
• Dump Power: power that will be available 50 % of the time.
• Maximum flow estimation: gives estimation of floods and helps in design of dam and spillway.
Site Selection for Hydropower Plants
• Availability of Water: Run-off data for many years available
• Water Storage: for water availability throughout the year
• Head of Water: most economic head, possibility of constructing a dam to get required head
• Geological Investigations: strong foundation, earthquake frequency is less
• Water Pollution: excessive corrosion and damage to metallic structures
• Sedimentation: capacity reduces due to gradual deposition of silt
• Social and Environmental Effects: submergence of areas, effect on biodiversity (e.g. western ghat), cultural and historic aspects
• Access to Site: for transportation of construction material and heavy machinery new railway lines or roads may be needed
• Multipurpose: power generation, irrigation, flood control, navigation, recreation; because initial cost of power plant is high because of civil engineering construction work