Flooding and Flood Risk

Storm Hydrograph (Flood hydrograph)

A graph that plots the increase of a river's discharge during and following a storm or precipitation event.

Lag time (hydrograph)

Time between peak rainfall and peak discharge

Rising Limb (Hydrograph)

The increase in river discharge as rainwater flows into the river

falling limb/recession

The decrease in river discharge over time after the precipitation event

levee

a wall of earth or concrete built up on either side of a river to prevent it from flooding its banks (a hard engineering technique)

Channelization

Anengineering technique to straighten, widen, deepen, or otherwise modify a natural stream channel.

deforestation

the action of clearing a wide area of trees - increases flood risk

Afforestation

This is a type of soft engineering technique. Trees are planted in the catchment area to increase interception. This is a cheap method of reducing flooding but can increase fire risk

dam

a hard engineering technique - a barrier that runs across a river or stream to control the flow of water

bioretention basins

gravel and/or sand filtration layers beneath reed beds and other wetland habitats to collect, store and filter dirty water

bioretention swales

same as bioretention basin but designed to filter and move water (usually at side of a street); filters out coarser particles and then finer particles get filter in the basin

Dam and Reservoir

A barrier(made on earth, concrete or stone) built across a valley to interrupt river flow and create a man‐made lake(reservoir) which stores water and controls the discharge of the river - a hard engineering technique

Lag time increases

in a rural drainage basin

Lag time decreases

in an urbanized drainage basin area

impermeable surfaces

pavement or buildings that do not allow water penetration

High portions of impermeable surfaces will

increase overland flow / surface run-off and increase flood risk

ABCs of water

Singapore's model of water and flood control - it should be active, beautiful, and clean

Green roofs

covering buildings with plants/grass - reduced stormwater runoff and has thermal benefits (keeps places cool and improves air quality)