PO9 - Take adequate and co-ordinated measures to reduce flood risks

Rainwater harvesting involves the collection and storage of rainwater at source for later use, for example, using water butts or larger storage tanks. Water butts are the most widely used and simplest rainwater harvesting technique, collecting rainwater runoff from roofs via a connection to the roof down-pipe. They are...

A floodplain is the area bordering a river that naturally provides space for the retention of flood and rainwater.  Because of regular flooding, floodplain soils are generally very fertile and they have often been dried-out to be used as agricultural land. Floodplains in many places have also been separated from the river by dikes, berms or other structures designed to control the flow of the...

Rain gardens are defined as small-scale vegetated gardens used for storage and infiltration. The term ‘rain garden’ is often used interchangeably with ‘bioretention area’ (although the latter could also be applied more loosely to other measures such as filter strips or swales). 

Permeable paving is designed to allow rainwater to infiltrate through the surface, either into underlying layers (soils and aquifers), or be stored below ground and released at a controlled rate to surface water. Permeable paving is used as a general term, but two types can be distinguished:

-       Porous pavements, where water is infiltrated across the entire surface (e.g. reinforced grass or gravel, or...

Channels and rills are shallow open surface water channels incorporated in to the start of a SuDS train. They collect water, slow it down and provide storage for silt deposited from runoff. They can have a variety of cross-sections to suit the urban landscape, and can include the use of planting to provide both enhanced visual appeal and water treatment. 

The main role of channels and rills are to collect runoff at the start of a...

Filter strips are uniformly graded, gently sloping, vegetated strips of land that provide opportunities for slow conveyance and (commonly) infiltration. They are designed to accept runoff as overland sheet flow from upstream development and often lie between a hard-surfaced area and a receiving stream, surface water collection, treatment or disposal system. 

Filter strips are generally planted with grass or other dense vegetation...

Infiltration trenches are defined as shallow excavations filled with rubble or stone. Their function is to facilitate the natural process of infiltration into the surrounding soils from the bottom and sides of the trench, thereby enhancing the soil's inherent capacity for drainage. Ideally, they should receive lateral inflow...

Dams and other transversal barriers are obstacles crossing the river section and causing discontinuities for sediment and fauna. Removing them consists in destroying all the obstacles, restoring the slope and the longitudinal profile of the river, therefore allowing re-establishment of fluvial dynamics, as well as sedimentary and ecological...

Soakaways are buried chambers that store surface water and allow it to percolate into the ground. They are typically square or circular excavations either filled with rubble or lined with brickwork, pre-cast concrete or polyethylene rings/perforated storage structures surrounded by granular backfill. The supporting structure and backfill...

Swales are broad, shallow, linear vegetated channels which can store or convey surface water (reducing the rate and volume of runoff) and remove pollutants. They can be used as conveyance features to pass the runoff to the next stage of the SuDS treatment train and can be designed to promote infiltration where soil and groundwater conditions...