Calculation of Abstractions Using GIS Gaurav Garg CVEN 689 Dept Of Civil Engg

Presentation Objectives Definition of Abstractions. Methodology –Data Gathering –Data Processing using GIS –Analysis using MS-Excel –Interpretation with GIS Results

Abstractions The part of the precipitation that does not contribute to the runoff. It includes- Infiltration Depression Storage Interception Evapo-Transpiration

Infiltration Techniques Richard’s Equation Horton’s Method Green and Ampt Method SCS Curve Number Method Initial loss plus Constant loss Method

Data Collection DEM for delineating watersheds STATSGO – Soils Data Polygons NWS – Weather Stations Points Green-Ampt parameters ( Clapp and Hornberger 1978) Assumed Uniform Precipitation

Delineating Watersheds Using CRWR-Prepro Main steps involved: - Flow Direction Flow Accumulation Stream Network Delineate Watersheds

Intersection Guadalupe Watershed Texas STATSGO

Watershed-STATSGO Soils Intersection

Procedure of Calculating Infiltration Green-Ampt Model Assumptions: 1)Soil is homogeneous with depth. 2)Infiltration wetting front is perfectly sharp and is same everywhere in horizontal. For this project a constant precipitation of 6cms for 2 hrs has been assumed.

Green-Ampt Equation f(t) = K h [1+( |Ψ f |*(Φ-θ 0 )] F(t) f(t) = infiltration at time t F(t) = cumulative infiltration K h = Hydraulic conductivity |Ψ f |= Suction Head (Φ-θ 0 )= Change in moisture content

Infiltration Results

Movement of Wetting Front

Questions