Not an expert on this, but you are on the right track.

thank u Mr.  Emmanuel

but after them by water balance equation we calculate ground water recharge ?!

  (P) = (Q + ET ± ∆GW ± ∆SM) .

Where:

P = Precipitation rate in (mm).

Q = Stream flow (mm/sec).

ET = Evapotranspiration rate (mm).

∆GW = Ground water storage changes in (mm).

∆SM = Change in soil moisture content (mm).

 Dear Sarbast: Thanks for the detailed listing of specifics in your question. Your water balance equations look fine. In implementing these, there are lots of assumptions you might be making about the watershed. With the use of one pan coefficient, you are assuming one type of land use. Another one is the last equation. Does your stream flow: it has base and storm flows. Thus a change in GW can be correlated with baseflows. You might need to check that. Given that your are using single sets of these balance equations, I am guessing you are lumping information for all watershed area. I recommend using a simulation model that is spatially explicit and use your streamflow and soil moisture observations to calibrate it. Best wishes on your work. 

thank u Mr. Timothy O Randhir  Good luck

Dear Friend,

Are we not taking in to consideration of the infiltration and percolation from the Tanks, lakes, canals and other water bodies existing within the catchment? Also field irrigation aspect followed by in fluent seepage of the rivers also matters towards the potential Evapo-transpiration and derivation of water balance?

The intricacy of the calculation of the water balance tends to increase with increase in area of the watershed or catchment. This is basically due to a related increase in the technical difficulty towards accurately computing the numerous important water balance components.

Considering the various inflow and outflow components in a given study area, the simplest groundwater balance equation can be written as:

                Rr  + Rc  + Ri  + Rt  +  Si  + Ig   =  E t  + T p  + S e  + O g  + ϪS                                                              

where,

                Rr   =       Recharge from rainfall;

               Rc    =      Recharge from canal seepage;

               Ri    =       Recharge from field irrigation;

               Rt    =       Recharge from tanks;

               Si    =       Influent seepage from rivers; 

              Ig    =        Inflow from other basins;

                                             =

               Et    =       Evapotranspiration from groundwater;

               Tp    =      draft from groundwater;

               Se    =      effluent seepage to rivers;

               Og   =      outflow to other basins; and

               ϪS  =        change in groundwater storage.

 Thanks,

Murali. K.

thank u  dear friends 

Murali k.

Dear friend

Are you using simulation model? I think that all the contribution made here are fine but try to use HEC-HMS to see the final result and compare.

Using the water balance (or budget) approach to build conceptual models is very common in hydrology.

However, I would recommend that you consider the 'linked linear reservoirs' method to write down the model algorithm. For your example, a three reservoir approach - upper, middle and lower reservoir will be appropriate. Starting with the upper reservoir, consider all inputs, outputs and storage change for it. Next, the output from the upper reservoir becomes input to the middle reservoir and will have its own outputs and storage changes. This process may be continued for any number of cascading reservoirs and the model algorithm may be written down. This approach will eliminate the possibility of double accounting for inputs and outputs.

For instance, I believe in your algorithm, precipitation input is appearing in both the soil zone as well as the groundwater zone which is incorrect.

Hope this helps. Good Luck!