With reference to a river catchment that you have studied, assess the potential impact of human activity upon the drainage basin

As cities expand through increasing urbanisation, the impacts of human activity on the drainage basin and, subsequently, flood risk are becoming clearer. From clearance of forest to covering of land with impermeable materials, on a growing scale these activities impact the cycle of water through a catchment e.g. slowing it down, speeding it up or reducing the space for it to flow. These changes can disrupt the hydrology of a drainage basin and affect flood risk e.g. by increasing flood magnitudes or concentrating them in built up areas. This highlights the importance of studying and understanding the impacts of human activity on a drainage basin.One of the earliest phases of human activity impacting drainage basins was the clearance of vegetation to make space for early settlements on flood plains; attractive for their flat land, access to drinking water and fertile soils. This reduces the amount of water absorbed by trees from the ground or intercepted as precipitation meaning more water reaches the channel as surface run-off. This effect is increased in built-up environments like Carlisle, which was subjected to extensive flooding in 2007. Cleared of vegetation, vast amounts of the area have gradually become covered with impervious surfaces, like concrete and tarmac, that stop water infiltrating and direct it to the river instead, further increasing the volume of water during a storm event. Traditional flood defences, like the flood embankment along the River Eden, Carlisle thought to be effective in reducing flood risk, reduced the space for the river and its increased flood waters. Combined, this activity has the potential to amplify the magnitude of flooding. The consequences of these floods are made worse by human development on flood plains, which is an example of humans putting themselves in harm’s way for economic benefits like farming. This is the case in Bangladesh where people are attracted to the River Brahmaputra for multiple reasons, increasing the human cost of flooding when it happens. The impacts on drainage basins are multi-layered and combined can have a devastating effect on floods that might, in a basins natural state, be more widely distributed and be associated with the delivery of life-supporting nutrients. The recognition of the impacts human activity is having has led to a more holistic approach to catchment management, involving making space for water e.g. flood embankments in Carlisle set back further from the river giving it more space to flood. This involves natural flood management methods like increasing vegetation across catchments and focussing on alleviation strategies that spread the distribution of flood waters and aim to reverse the effects of previous activity that may have concentrated flood waters in one “weak point” of the river.