1. Runoff in MIKE-SWMM
Melissa Figurski

2. Subroutine Schematic
OVRLND subroutine does runoff.

3. Surface Flow Routing Elements
Subcatchment (overland flow)
Channel (trapezoidal/parabolic channel flow)
Pipe (circular channel flow)
Control Structures (weirs and orifices)

4. Discretization
“Mathematical abstraction of the physical drainage system”
Turn basin into rectangles
Fine vs. Coarse Discretization
How the computer sees your basin. More on pg. 80

5. Discretization

6. Subcatchment Overview
Discretize basin into subcatchments
Calculate runoff from each subcatchment
Combine outflow from each subcatchment for total runoff
Total runoff is computed through a

7. Subcatchment Subareas
Three subareas in each subcatchment represent impervious w/ storage, impervious w/o storage, and previous w/ storage. Actually, subcatchment can consist entirely of one or more types of subareas.
Width of impervious area is ratio of impervious area to total impervious area.

8. Non-linear Reservoir d2 – d1 = i* + WCON [d1 + 0.5(d2 – d1) – dp]/5/3
Manning’s equation for flow. W is width of subcatchment. Non-linear eqn. from combination of Maning’s and continuity equation. Eqn. for time step – solve for d2 with Newton-Raphson method. Plug d2 into Manning’s equation for outflow in that period. i* = rainfall excess
d2 – d1
= i* + WCON [d (d2 – d1) – dp]/5/3 Dt
1.49 W S1/2
WCON = –
A n

9. Reference Storm Water Management Model: Version 4, User’s Manual.
Section 4: Runoff Block,
Appendix VI