flood risk and management

Answer: Urbanisation increases flood risk because impermeable surfaces like tarmac and concrete prevent rainwater from infiltrating into the soil (1 mark), causing up to 95% of rainfall to become surface runoff compared to 10% in natural areas (1 mark). Storm drains and culverts carry this runoff rapidly into rivers, shortening lag time (1 mark). This creates a flashy hydrograph with rapid rise and high peak discharge, increasing the likelihood of the river exceeding channel capacity and flooding (1 mark).

Answer: Urbanisation increases flood risk because impermeable surfaces like tarmac and concrete prevent rainwater from infiltrating into the soil (1 mark), causing up to 95% of rainfall to become surface runoff compared to 10% in natural areas (1 mark). Storm drains and culverts carry this runoff rapidly into rivers, shortening lag time (1 mark). This creates a flashy hydrograph with rapid rise and high peak discharge, increasing the likelihood of the river exceeding channel capacity and flooding (1 mark).

Answer: A flashy hydrograph has a steep rising limb showing that discharge increases rapidly after rainfall begins (1 mark). The peak discharge is high, meaning the river reaches a large volume of flow (1 mark). The lag time between peak rainfall and peak discharge is short, typically just a few hours (1 mark). The falling limb is also steep, showing that discharge decreases quickly once rainfall stops (1 mark). This type of hydrograph is typical of steep, impermeable or urbanised drainage basins.

Answer: Hard engineering uses artificial structures like dams and flood walls to control water and protect property (1 mark). Dams are very effective at regulating flow but are expensive (£20M+) and flood valleys upstream (1 mark). Soft engineering works with natural processes like flood warnings, flood plain zoning and afforestation (1 mark). Flood warnings save lives cheaply but don't prevent damage (1 mark). Hard engineering is more immediately effective but can create problems downstream and is costly to maintain (1 mark). Soft engineering is more sustainable and environmentally friendly but may be insufficient in extreme events like Storm Desmond (1 mark). A combination of both approaches is most effective.

Answer: Cockermouth in Cumbria has experienced repeated flooding, most severely in 2009 and 2015. After the 2009 flood, a £4.4 million hard engineering scheme was built in 2013, including a 250-metre flood wall and embankments designed for a 1-in-100 year event (1 mark). This was initially effective for moderate floods but was overtopped by Storm Desmond in 2015, which brought 405 mm of rain in 48 hours, flooding over 500 properties (1 mark). This shows that hard engineering has limits when extreme events exceed design capacity (1 mark). Following 2015, a revised approach was adopted combining enhanced hard defences (higher walls) with soft engineering including improved flood warnings, upstream water storage and flood resilience measures for properties (1 mark). Keswick's £7.1 million scheme (2017) combined embankments with a pumping station (1 mark). The effectiveness of management in Cockermouth is mixed - defences reduce the impact of moderate floods but cannot eliminate risk from extreme events (1 mark). Climate change is increasing the frequency of severe rainfall, making 1-in-100 year events more common (1 mark). The most effective long-term approach is an integrated strategy combining hard defences where needed, soft engineering to slow runoff, flood warnings to protect life, and planning to restrict development on flood plains (1 mark). However, complete protection is impossible, and communities must also build resilience to accept and recover from flooding (1 mark).