1. Distributed Overland Flow Modeling ABE 527 Rabi H. Mohtar Associate Professor Reference: Applied Hydrology, Chow (Maidment/Mays McGraw-Hill, 1988)

2. Types of Overland Flow (1) Hortonian Overland Flow “Neglecting interception by vegetation, surface runoff is that part of the rainfall which is not absorbed by the soil by infiltration” Horton, 1933 It is also called “rainfall excess” = (r-i)

3. Types of Overland Flow (2) Saturation Overland Flow When subsurface flow saturates the soil near the bottom of a slope and overland flow occurs as rain falls onto saturated flow. Occurs at bottom of hills and near stream banks. Also on vegetated areas in humid regions.

4. Deterministic Hydrologic Models A. Lumped Steady: SCS Curve Number B. Lumped Unsteady: Unit hydrograph or Linear System Theory C. Distributed Steady: Channel flow with no lateral inflow D. Distributed Unsteady: Channel flow with lateral inflow, Overland flow.

5. Flow Routing Definition To determine the time and magnitude of flow (hydrograph) at a point on a watercourse from known or assumed hydrographs at one or more points upstream. Can be lumped or distributed.

6. Lumped Flow Routing Routing through one point such as the outlet. Continuity equation: S is Storage, I is the inflow and O is the outflow

7. Lumped Flow Routing Level Pool method (flow through reservoir): S=f(O) Muskingham method: S is linearly related to I and O Linear Reservoir method: S is a linear function of O and its time derivatives.

8. Distributed Overland Flow Routing de Saint Venant Equations: Continuity: Inflow: Outflow: Q=flow entering the control volume of the overland flow section q=lateral inflow entering the control volume

9. Distributed Overland Flow Routing Continuity: Storage: Conservation form

10. Distributed Overland Flow Routing Continuity: For a unit width: Q=Vh and A=h Nonconservation form

11. Distributed Overland Flow Routing Momentum: Forces: Gravitational Force: Friction Force: Pressure Force:

12. Distributed Overland Flow Routing Momentum:

13. Distributed Overland Flow Routing Momentum: Momentum Inflow: Momentum Outflow: Stored Momentum: