This NBS focuses on the delivery additional ecological components withina hard/built engineered approach to water management. They aid thereduction in pluvial flood risk in urban areas and improve the quality ofwater within sewerage systems. The main approaches and benefits of harddrainage flood prevention are:

• Hard drainage flood prevention includes river engineering and damconstruction to control the amount of discharged.
• Dams can be built to hold water back and release it in a controlled way. Water is held in a reservoir behind the dam, and can provide an additionaluse, such as hydroelectric power or recreation.
• The river channel may be widened or deepened allowing it to carry morewater. A river channel may be straightened so that water can travel fasteralong the course. The channel course of the river can also be altered,diverting floodwaters away from settlements.

Considerations in designing hard drainage flood prevention: The dam specifications need to consider sediment trapping behind the dam wall,which can lead to erosion downstream. In addition, altering the riverchannel may lead to a greater risk of flooding downstream, as the water iscarried there faster.