Factors Affecting River Discharge and Flooding

Factors Affecting River Discharge and Flooding

• Deforestation: Removal of trees reduces water absorption by roots, increasing surface runoff and river discharge, potentially leading to flooding.

• Urbanisation: Increased impermeable surfaces (tarmac, concrete) result in more rapid surface runoff, faster flow into rivers, and a greater flood risk.

• Agriculture (Farming): Arable farming (crop growing) practices with ploughing create furrows that increase water velocity and river discharge, contributing to flooding.

• Relief (Land Shape): Steep slopes lead to faster surface runoff, higher river discharge, and increased flood risk.

• Precipitation: Rainfall, snowmelt, and other forms of precipitation directly increase river discharge and water table levels; prolonged rainfall can saturate soils and contribute to flooding.

• Geology: Permeable rocks allow water to soak into the ground, reducing surface runoff. Impermeable rocks lead to more surface runoff and increase flood risk.

River Features and Processes

• Floodplain: A wide, flat area on either side of a river, characteristically lower river course, formed by deposition during floods. Floodplains are composed of alluvium (sediments).

• Floodplain Formation: Formed by deposition of sediment during floods or lateral erosion by meandering rivers that erode valley sides.

• Waterfall Formation: Forms where hard rock overlies soft rock; hydraulic action and abrasion erode soft rock, undercutting the hard rock that collapses into a plunge pool, with ongoing erosion moving the waterfall upstream.

• Meander Formation: A bend or loop in a river; deposit building on the inside of the bend, erosion and loss on the outside of the bend.

• Watershed: The land area that feeds water into a particular river system. A river begins at a source, flows to a confluence (where two rivers meet), and ends at a mouth (where it meets the sea). Tributaries are smaller rivers or streams that join a larger river.

The Hydrologic Cycle

• Solar Energy Drives the Cycle: Sun heats Earth's surface, leading to evaporation from water bodies and vegetation.

• Evaporation, Condensation, Precipitation: Warm air rises (with water vapor), vapor turns to liquid water droplets during condensation, producing clouds. Heavy clouds result in precipitation (rain, snow, sleet, hail).

• Water Distribution Post Precipitation: Precipitation that reaches the land can run directly into rivers/oceans, be absorbed by soil and vegetation (infiltration), evaporate from leaves, or become overland flow back to rivers/oceans.