Residential and commercial development projects in natural floodplains remove or reduce water storage capacity, and often cause flooding both up and downstream. Artificially controlling stormwater, in an effort to keep it out of the floodplain, causes the water to overflow riverbanks in other locations. This often creates floods of greater magnitude and danger. Building on floodplains increases the risk of property damage and life-threatening conditions. Diverting stormwater into channels forces the water to flow faster, and this both erodes topsoil and destroys habitats.
In addition to building construction, several other activities contribute to an increase in flooding.
- Removal of stabilizing vegetation along stream and river banks
- Structures that deflect or inhibit the flow of floodwaters
- Structures (e.g. bridges, culverts) that encroach on the floodplain and reduce water storage
- Drainage systems that conduct stormwater too quickly into receiving rivers and lakes
- Backfilling and dumping debris that interfere with the movement of floodwater
- Impervious surfaces (pavements) that prevent the soaking, seepage, and storage of rainfall.