- wide and low-lying plain found on both sides of a river
- covered with alluvium deposited by the river

Levees:
- natural embankments found along the banks of a river
- made up of coarser alluvial deposits than the flood plain 

When a drainage basin has little or no vegetation to intercept the rain, a greater volume of water in the surface runoff quickly adds to the volume of water in the river. 

2. Heavy rain - river overflows its banks and floods surrounding areas. Extensive flat lowlands --> larger wetted perimeter --> Water encounters friction --> increased friction reduces speed of water --> deposition of materials on both sides of river

3. coarser heavier materials are deposited first, hence nearest the banks and finer lighter materials are deposited further away from the banks

4. repeated flooding will cause the alluvial deposits to accumulate
the coarser material at the river banks form raised embankments called levees
the finer materials forms the floodplain
although floodplains and levees are more common at the lower course, they can also develop between the middle and lower course

The torrential rain brought about by tropical cyclones causes river levels in the affected areas to rise significantly in places like bangladesh. The amount of water in rivers in equatorial areas increases whenever heavy rain falls in the afternoon. 

When the temperatures experienced in a region are very low and much water is held in the form of ice and snow, the water level in rivers is low. When the temperature rises, the volume of water in rivers increase as water from the melting snow and ice flows into them.

Permeable rocks like sandstone, chalk and limestone which have coarse grain size and large pore spaces allow water to infiltrate easily. 

Impermeable rocks like shale, clay and granite which have tightly packed small grains go not allow water to pass through. 

When water flows through an area of permeable rock, more water infiltrates the ground. As a result, there is low surface runoff and this leads to a lower volume of flow. 

When water flows through an area of impermeable rocks, there will be little water infiltrated into the ground and thus leads to high surface runoff and volume of flow is higher. 

Vertical erosion: Occurs when rocks and other materials on the river bed are removed, causing the channel to become deeper 

Horizontal/Lateral erosion: Occurs when rocks and other materials along the sides of the channel are worn away. This causes the river channel to become wider. 

 

4 types of processes involved in erosion: 

-Hydraulic action 

-Corrasion 

-Attrition 

-Solution 

The wetted perimeter refers to the total length of the river sides and bed.

The greater the wetted perimeter, the greater the friction between the water and the banks and the bed of the channel, and the slower the flow of the river. 

If both rivers have the same cross-sectional areas, the one with the larger wetted perimeter flows slower than that of a small wetted perimeter because of more friction. 

Erosive agent: Rock fragments 

Erosive agent: Carbonic acid in water