Administrative/ non structural measures ( 08-05-2011 L: 4)

The main idea is to keep the general civil & industrial activities undiminished during flood which can be ensured by

# Flood forecasting wearing systems, flood regulation through zoning, emergency plans, modifying building codes, flood proofing, disaster preparedness and existence.

# Automatic ranging stations provide reliable picture of the rainfall events of the basin, Radar data provide details with regard to movement and dynamic characteristics of storms at a large scale.

# a useful input to the forecast is the meteorological satellite data. Relative forecast are issued now a days in many countries for important rivers. The rainfall details, catchment details, river geometry, discharge, water level etc.

Design flood: It is adopted for the design of a structure. The term design flood is frequently used to denote the maximum discharge that can be passed in a hydraulic structure without any damage to the stability of the structure. Information of flood magnitudes and their frequencies is needed for the design of hydraulic structures such as dams, spillways, road and railway bridges, culverts, urban drainage system etc.

a)   Ordinary flood: It is likely to be equaled in magnitude once or more times in the estimated life of the project.

b)   Standard project flood: The flood that would result from a severe combination of meteorological and hydrological factors that are reasonably applicable to the region. Extremely rare combinations of factors are excluded.

c)   Parabolic maximum flood: The extreme flood that is physically possible in a region as a result of seven most combinations, including rare combinations of meteorological & hydrological factors.

Methods for estimating floods:

a)   Rational method

b)   Empirical method

c)   US- soil conservations service curve number method

d)   Flood frequencies studies

Rational Method: Considering a rainfall of uniform intensity and long duration occurring over a basin,

      

                      Q_p = CIA     for  t ≥ t_c

Here,

         Q_p  =  Peak runoff

         C   =  Coefficient of runoff

          I   =   Intensity of rainfall

         A   =   area of catchment

         t_c   =   The time taken for a drop of water from the farthest part of  

                    the catchment in outlet.