Different types of wetlands play important flood control roles in different situations. In the upper reaches of some river basins, for example, peatlands and wet grassland can act like sponges (saturated peat is typically up to 98% water by mass), absorbing rainfall and allowing it to percolate more slowly into the soil, thereby reducing the speed and volume of runoff entering streams and rivers. This means that water levels in larger channels, further downstream, also rise more slowly and human lives and livelihoods are less likely to be affected by destructive flash flooding.
In 1982, an earth dam within the US Rocky Mountain National Park collapsed, resulting in the sudden release of nearly one million cubic metres of water. A wall of water up to 10 metres in height swept downstream, entering Fall River at Horseshoe Park. Fortunately, in this area, wetlands adjacent to the river – including meadows with dense stands of reed and willow – slowed the flood wave, which spread out across the wide floodplain. The surge, reduced to a 3-metre wave, was finally contained by another dam downstream. The disaster claimed four lives and resulted in over US$30 million in damage (1982 prices). However, without the Horseshoe Park wetlands the catastrophe would have been even worse.