Question

Summarize the advantages and disadvantages of the Ø-index approach over the Green Ampt method for estimating infiltration losses for a storm. (clear writing or typing)

Answer 1

• D Ans: Green- Ampt method for Computing Infiltration Rate and Quantity of Infiltration, suggested an analyliftical solution to the problem of Ground Infiltration. This method now a days used for preparing computer models for computing the infriltration rate and total infiltration resulting from a rainfall. d -index - for large dramag basins, the rain intensily cannot be considered uniform Over the entive area, and non-off does not respond auickly to the rain full pattern. Therefore, Green - Ampt method described to determine infiltration Capacity curve for small basin is not applicable to larger basin... That Therefore, Horton has develop a method of determining of infiltration capacity of lage dramage basins. It is not possible to determine Infiltration Capacity Curve for lage basin. Only the owerage. values can be detenine for their infiltratation capacity. The finder during or storm for a given catchment generally depends upon the type of catchment soil, vegetative cover, initial mostime content, storm duration, and at its intensity :

A complete detailed information on somang variables for a pesticuler catchment is generally very relaz diff difficult and an expensive exercice s Hence, for practical purpose, certain simplification are made for estimation of flood magnitude of due to critical storms, by making certain tolerable assumptions and not Since, the maximum floods peases are invariably produced byd long duration storms and usally in the weet season, the initial losses are assumed to be negligibly small. More over only to two factors, ie. (i) the soil type and in rainfall are found to be critial in the estimation of 8- index. for maxium flood producing storm. Advantages of p-index over Green Ampt &- indy Green - Ampt. most common method to Time based model, and a predict run-off & docsult can simulate impacts of consider rainfall intensitt rainfall intensition & duration and duration, only and infiltration process. total rainfall volume. 1 very simple model. u very complex molt and required help of computer molt to computer TPg - 2/4

0 index Green - Ampt. . Actual data from an Assumption taxen from as • type of soil and volume soil profile is Homogeneous & • of rainfall is consided Uniformly antecedent moisture 3 to compete 8-inden. distributed in the catchment area and the soil above the wething front is considered to se completely satinated. 2 Only Rainfall amount (1) Rainfall intencity & Rainfall in voln & soil type distribution model for prepared is considend – hence for compution of Infiltration Rate 3 very simple model. & Guantity. Hence-very complos model • Simple approach on Complex approach considered antecedent moistine antecedent soil - water storage Condition of hydrologic (volume) by soil layer or soil 2 soil group. depth. Soil-water properties ie. butk density, saturated Conductivity and water entry or bubbling pressue. 5 w simple approach on complex approach on total 3 assumption of initial infiltration prior to surface ponding abstraction assumed as infiluenced by topography, land un and ground cover. An

Disadvantage of p_index over Green- Ampt. ② As expected the Green - Ampt simutation presented an overall better performance compared to as the l-index simulations, @ Green - Ampt can better represent the stom events of a tropical climate. (11) for dry and oth wet period the Green-Ampt a presented a slightly advantage to the 8. index method and for the average periode the diners present a better result but methods failed to represent the rainfall events of 1 The main cause for the superior performances of the Green - Ampt method is because it is a plugesically - based infiltrationt excess, rainfall - non off modet, and is therefore not suitable for regions where the rainfall & rate seldom exceeds the satmated conductivity of the soil, which is not the case in Brazil. 1 - End T Pg 4/4