Following formulae are used to calculate the rainfall-runoff relationship. The Rational equation is the simplest method to determine peak discharge from drainage basin runoff. 4) Inglis’sformula : developed for western India. INGLIS AND DE SOUZA'S, LACEY'S, PARKER'S BRITISH AND USA, AND TAPI BASIN Formula use for corelationship. R= 0.85 P - 30.5 Where in, R= Runoff (in mm) P= Precipitation (in mm) 2) Khosla’s Formula: best estimates, followed by the Khosla`s formula, the rational method was the last. empirical runoff estimation method including Dredge & Burge, Bourges, Inglis, Faning, Hyderabad, Burkli Ziegler, Cramar and Possenti were calculated in Bakhtegan watershed which is located in Fars province. Some of the leading empirical formulae for estimating the storm water (or rain water) flow or runoff are given below: Inglis formula was derived by using the data of catchment areas or drainage areas of Maharashtra where it is commonly used. From rainfall records 2. Runoff or streamflow comprises the gravity movement of water in Rational Equation: Q=ciA The Rational equation requires the following units: Ali Nawab Jang Bahadur formula: ( 0.993Q= CA - 1/14 log A) Where, Q= Discharge in Cumec A=area of catchment insq .km 1) Sir Inglis Formula: Ghats fed Catchment (i.e. Inglish formula is derived by using the data of rivers of Mahashtra, where it is commonly used. For Ghat regions of western India, R = 0.85 P – 30.5 2. Inglis formula: • Q= 124 A = 124 A ½ √A + 10.4 Where Q= discharge in cumec A= area of catchment in Sq.. Km. Inglis formula (1930) Where Q p = maximum flood discharge (m 3 /s) A = catchment area (km 2) 4. Inglis and Disooza (1929) [6] developed regional formula between annual runoff (R) in cm and annual rainfall (P) in cm for different regions of India, given as: 1. Khosla’srelationship for runoff estimation is given by Rm = Pm –Lm Lm = 0.48 Tm ( Tm > 4.5OC ) Rm = monthly runoff in cm Pm = monthly rainfall in cm Lm = monthly losses in cm Tm = … Empirical formulae a) Khosla’s formula R-Annual run-off in mm. It is not as sophisticated as the SCS TR-55 method, but is the most common method used for sizing sewer systems. 10 124 A A Q P Contd… Originally developed for the catchments in Western Ghats in Maharashtra At present this is used all over in Maharashtra with a modification in the numerator (the value of 124) b) Inglis formula for areas of Maharashtra For ghat region, For plain region, R = 0.88 P – 304.8 R = (P-177.8) x P / 2540 R = P - 4.811 T Run-off over the catchment = rainfall x coefficient 10. T-mean temperature in ˚C. the western slopes of western Ghats receiving heavy rain from the south west monsoon winds). To Calculate Runoff for Morbe Dam Project, The INGLIS Method is used. Qe= 0.7356 P- 12 Where, Qe= Estimated runoff in cms P= Rainfall in inch The results obtained from the above empirical formula are shown in Appendix: 3, In which it is shown that there is a huge difference between estimated and observed runoff, So INGLIS After studying empirical methods for annual flood flow rate estimation and comparing the 5) Khosla’sformula: developed for time period of the month. P-Annual rainfall in mm.