Rainfall Rnoff Model Lab Report

RAINFALL RUNOFF MODELING

INTRODUCTION

A Mathematical model is a description of a system using mathematical concepts and the process of making mathematical model is called mathematical modeling. It is usually composed of relationship between mathematical operators and system variables.

Rainfall runoff modeling: A Rainfall- Runoff model is a mathematical model describes the relation between rainfall and the runoff of the catchment or watershed. It gives the output runoff hydrograph for a given input rainfall hydrograph. Whenever the surface runoff estimates are reliable then only the policy makers make optimized decision on water resources planning and management. Runoff of the catchment is basically depends on rainfall characteristics (duration,

are the model parameters

Simple process equation (tanh equation):

R=P-a-b tanh {(P-a)/b}

This equation provides physical process in the catchment. Here a and b are model parameters. And a represents maximum rainfall below that runoff will not occur. (Includes interception and soil storage), b represents the factors controlling additional rainfall losses. This equation is also a different form of US Soil Conservation curve number.

Simple time series equation (Tsykin equation):

This equation relates runoff to the rainfall in current and previous periods.

R=a + b〖〖 P〗_i〗^c . 〖P_i〗^d. 〖P_i〗^e......... a, b, c, d, e are model parameters. This equation gives better results than the time series equation.

Complex daily time series model: (IHACRES)

This model uses more empirical equations.

〖EX〗_i =z P_i S_i

Here, EX is rainfall excess, z is a factor relates the equivalence in rainfall excess and total runoff recorded in a same time and S is the storage in i th period.

Si=P_i+ (1-〖τ_i〗^(-1))Si-1 τ_i is catchment wetness index depends on temperature and storage on previous day τ_i= τ exp f (20-Ti) exp (-pSi-1) here, T is the temperature and τ , f, p are model