Solution by Trial and Error Method

Make a table as shown in Table0.0 Choose time interval of 4 hours and enter these values in column(1) of this table.

  • In column (2) enter reservoir levels at start of each time interval.
  • Calculate inflow of flood and enter its values in column 3 for each time interval.
  • Now using discharge-elevation curve of Fig. 9.13 find out the discharge over spillway at the start of each time interval corresponding to level of water in column (2) and enter them in column 4.
  • Assume trial elevations, and enter them into column (5).
  • For these trial elevations, calculate spillway discharge and enter them in column (6).
  • Determine the mean outflow rate by taking mean of column (4) and column (6).
  • Enter mean values in column (7).
  • Convert the values of column (7) into outflow volume in m3 and enter in column(8).
  • The volume of outflow will be less than inflow volume so long as the peak of flood has not been routed.
  • Once the peak of the flood has been routed, the volume of outflow exceeds the inflow volume.
  • At this Lillie it is considered that maximum flood conditions have occurred.
  • find the storage capacity between the reservoir elevation at the beginning and end of the period.
  • Enter all such values in column (9) Add columns (8) and (9) and enter in column (10).
  • Figures in column (10) show the sum of outflow volume and storage capacity.
  • Find out the difference between corresponding figures of column (3) and column (10) and enter in column (11).
  • This difference between figures of column (3) and (20) should be negligible. Any remark may be written in column (12).
  • The trial and error method in Tables 9.3 and 9.4 can be replaced.