Surface water + flooding

Main 3 ways rain disperses

• surface runoff

• infiltration

• evapotranspiration

main things that impact rain dispersal

• vegetation type

• land slope

• soil type

what determines the drainage basins boundaries

upstream topography

outline the bucket model

in = rain

out = infiltration and Q

volume = SA

Q = λV

ds/dt = R - I - λS

flow speed for 1D model

ro*g*sinθ*(k/µ)

Q for flow in river

A(h) * u(h)

how to find Q*

Q* = Q(h*)

controls to reduce floods in rivers (ranked)

1. widen river

2. raise levees

3. deepen river

what is h*

height where river overflows

where resevoirs are usually built

upstream

u for Q_o of resevoir

√(2gh)

Q_o for resevoirs

uA₀

dv/dt for resevoir

Q_in - Q_o

h_eq = (at steady state)

Q_in² / A₀² * 1/(2g)

sediment problems

• no sediment downstream

  • can lead to net erosion of the banks

  • less nutrients so lowers soil quality

• builds up in resevoir

  • can break hydroelectric turbines and generators

how to remove sediment

resuspend it

Shields criterion

Fs > 0.06(ro_s - ro_w)*g*d_s

Shear force for sediment resuspension

Fs = ƒ*ro_w*u²

added force on car when flood occurs (buoyancy)

ro_w*g*h*A

Force on car from flood

F = C_D*ro* u²*A