Since the mid-20th century, intensive water consumption has dewatered the lower 100 miles (161 km) of the river such that it no longer reaches the sea except in years of heavy runoff.

The failure of the dam, combined with heavy runoff from the storm, turned the usually small creek into a massive torrent that washed through central Rapid City.

The pool also had frequent boiling eruptions on August 15, 1991, doming the water to 3 feet and causing heavy runoff.

The airport caused heavy runoff into the Little Savannah, Long Branch, and Pumpkintown communities.

A cloudburst 15 miles away sent heavy runoff down a normally dry wash in Antelope Canyon toward the unsuspecting sightseers.

The average flow of the river is very low, only a few cubic metres per second, but much higher flows are possible during periods of heavy runoff.

The upper reaches of the Leon do not facilitate recreational use since the river only has sufficient water during periods of heavy runoff.

However heavy agricultural runoffs as well as municipal sewage have created severe pollution problems in the river.

Dog Canyon was carved into the basin fill materials of sand, silt and clay by heavy runoffs of earth and water from the surrounding mountains.

The 1983 flood was caused by an El Niño event causing heavy runoff from the overdeveloped watershed.