Flood is a natural even which has always been an integral part of geological history of earth. It occurs along rivers, streams and lacks.
- Most of the hydraulic are designed on flood record.
- Small hydraulic structures are based on a minimum of 25 years flood records e.g all structure constructed in the canal, soil conservation practices etc.
- Medium type structures are mainly based on 50 years flood records e.g culverts, drainage structures and waterway structures.
- Large irrigation projects are based on 100 years of flood record e.g Dams, reservoirs, headwork’s, barrages.
Intensive rainfall and high melting of snow are two main causes of flood.
- These factors are given as fallows
- Main made activity:
- Aforestation and deforestation
- Intensive rainfall:
- High flood occurs due to intensive rainfall.
- Slop of Catchment.
- Magnitude of Catchment
- Soil type.
- Catchment shape.
- Improve drainage system/poor drainage system.
- Climatic changes.
- Form of precipitation.
- Water logging
- Check on deforestation and well planed watershed management project
- Check dams and reservoirs
- Distribution of water at various streams
- Empowering drainage system
- Decrease water logging
- Construction of levees and improvement of steams
- No method is available for knowing the exact amount and intensity of rainfall by which flood can be determined
- Similarly rainfall and flood prediction cannot be performed but with certain precision
- The expected flood and its consequent damage can only be judged and appointed and hence while designing flood protection and judgment of design engineer is of utmost importance
- Various methods have been used for flood estimation
- Some methods are based on basic characteristics and others are based on the theory of probability by using previous flood data and some others are based on the study of rainfall and runoff data
- From marks of height flood on rivers bank, the area of flow the Wetted parameter and slope can be found
Peak discharge can be calculated from Mannig eq. Q = 1/n R2/3 S ½ A