Man-made drainage could raise risk of flooding

June 13, 2014 by Alex Peel, PlanetEarth Online
Man-made drainage could raise risk of flooding

Installing drainage systems in developing towns and cities can cause water to reach rivers more quickly, potentially raising the risk of flooding, say scientists.

New research, published in the Journal of Hydrology, says storm can result in higher peak flows that rise and recede more quickly.

It suggests that, in some cases, storm drains may do more to increase the risk of flooding than changes in the .

Its authors hope their research will help to guide future planning decisions, particularly in areas where the city meets the countryside.

'When we're thinking about urban developments, we need to start thinking about the land use in terms of its hydrological impacts,' says James Miller, of NERC's Centre for Ecology & Hydrology, who led the study.

'It's not just the changes at the surface that matter – what goes on beneath with drainage and the retention of water is just as important.'

'New tends to be really dense, and requires a lot of engineering. Allowing for some space and design would be really beneficial in some places, but the planning issues are very entangled.'

The team measured rainfall, runoff and evaporation in two adjacent river catchments in Swindon, UK, over 2011 and 2012. One was heavily urbanised, while the other was relatively new fringe development on previously rural land, which scientists call 'peri-urban'.

The peri-urban catchment contained two distinct drainage systems – one with a mixture of natural and man-made drainage, the other dominated by a storm drainage system.

Analysis showed that influenced the speed at which water reached the river more than either impermeable land cover or the type of development.

The team also used historical maps to simulate the hydrological effects of urban from the 1960s to the 2010s.

They found that, following the introduction of a large-scale storm drainage system to the peri-urban area in 2010, floods lasted half as long on average, but peak river flows increased by over 400 per cent compared with the 1960s.

The team are now monitoring rainfall and runoff across a number of urban catchments throughout the UK.

A recent study by the Met Office and Newcastle University predicted that global warming could cause extreme summer downpours to become several times more frequent in the UK by 2100, potentially leading to more flash flooding.

'Storm drainage is needed to quickly remove water from impermeable land in towns and cities,' says Miller. 'But future developments will need to consider how they will mitigate the combined effects of this and the possibility of more frequent intense storms.'

Explore further: Tracking urban change and flood risk with Landsat satellite

More information: James D. Miller, Hyeonjun Kim, Thomas R. Kjeldsen, John Packman, Stephen Grebby, Rachel Dearden, "Assessing the impact of urbanization on storm runoff in a peri-urban catchment using historical change in impervious cover," Journal of Hydrology, Volume 515, 16 July 2014, Pages 59-70, ISSN 0022-1694, DOI: 10.1016/j.jhydrol.2014.04.011.

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5 / 5 (3) Jun 13, 2014
Drainage systems which dump water into streams and rivers are the exact opposite of what is needed in a climate of extreme rain and drought. What is needed, instead, are berms and flood plains, and percolation ponds to catch large surges of rain and then letting this water slowly percolate into the water table, thus replenishing the water table for times of drought.
5 / 5 (1) Jun 13, 2014
I understand that pre-Columbian Americans built levees to *retain* water, mitigating flooding, slowing river flow, and replenishing the soil of the bottom land. They also built their homes on high ground or atop the levees.
Uncle Ira
4 / 5 (4) Jun 13, 2014
Flood plains on the rivers is just as important as the wetlands on the coast. That is because they act like a shock absorber for the big water him. The more water you dump fast into the river, the more flood plain you need. Building the levee bigger just make the problem more bad for somebody else somewhere else. If you pave over the flood plain and also dump that water too in the river even faster, it only make the flooding worster for the everyone except the one who happen to have the biggest levee. And maybe also the man who lives sometimes on the flatbottom houseboat.

Is the same on the wetlands, if you drain them out, the big storm will hit you harder him. And if you dig the canals in through them, the salty water will kill off the marsh and the wetland will recede inland then there will be nothing left to shock absorb the big storms. You don't got to be the smart scientist-Skippy to know about this, all you got to do live near the water all along for your life.
Jun 14, 2014
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