Understanding Flooding and River Dynamics

What is a flood?

The flow of water outside the normal course of a stream or river, usually due to too much water trying to flow through the system at one time.

How do rivers form?

Water flows downhill, carving channels through erosion, which become deeper and capture more water, leading to a drainage network.

What is a drainage network?

Consists of small streams flowing into bigger streams, which flow into rivers and eventually into the ocean.

What happens to water flow as a river curves?

Water moves at different speeds; it slows down on the inside of the bend and speeds up on the outside, causing erosion on the outside and deposition on the inside.

What is a meander in a river?

A curve in a river that moves outward by cutting into the outside bank, causing the river to wander across the valley.

What is a floodplain?

A wide flat valley floor created by sediment deposited on the inside of meanders.

What is discharge in the context of rivers?

A measure of river flow, defined as the amount of water flowing through the river, calculated using the formula Q = Area x speed.

What factors influence the flow speed of a river?

Gravity, slope, and the amount of water in the river.

What is equilibrium in river systems?

When upstream discharge equals downstream discharge, maintaining a balance in the river flow.

How do natural levees form?

Form during floods when sediment is deposited along the banks, building them up over time.

What effect do levees have on river profiles?

Making it steeper and deeper, which can protect nearby land but may lead to land subsidence without regular flooding.

What is runoff?

Water that flows downhill after rain, calculated as Runoff = Rainfall - Evaporation - Infiltration - Interception.

What factors affect infiltration?

Affected by ground type, soil moisture, and vegetation; frozen or compacted soil has low infiltration capacity.

What is interception in hydrology?

The temporary storage of water on its way downhill, occurring on surfaces like leaves or in ponds.

What are flash floods?

Occur when there is little or no infiltration capacity, causing all rain to become runoff quickly, often in steep areas.

What is channelization?

The alteration of a river's profile to make it steeper and more canyon-like, often through dredging or building levees.

How do dams help with flood control?

Create lakes that store water, increasing interception and allowing for controlled downstream discharge.

What are retention ponds?

Temporarily store water, increasing interception and slowing runoff to reduce peak discharge.

What is the purpose of floodways?

Undeveloped sections of floodplains that allow rivers to overflow safely during high flow.

What are zoning laws in flood mitigation?

Regulate the types of buildings that can be constructed in flood-prone areas to reduce flood risk.

How do insurance companies influence flood risk?

Insurance companies charge higher premiums for flood insurance in flood zones and may require coverage for mortgages.

What is the average annual cost of flood damage in the US?

The US spends more than 8 billion dollars per year on flood damage.

How many people die each year due to floods in the US?

Almost 100 people die each year as a result of flooding.