Here’s is a look at the Colorado River drainage basin. And here is the Great Basin, next door to the north and west of the Colorado. As mentioned, water that falls as rain in the Colorado river drainage has the chance to end-up back in the ocean, but almost all (if not all) fresh water falling within that basin ends up getting transported and used by humans, or lost to evaporation. If a downpour occurs anywhere upriver from Hoover Dam, then that is a bonus run-off that likely gets captured in Lake Mead. Monsoons in central AZ around Phoenix and Tucson end-up in the Gila River, which feeds the Colorado, but downstream from Hoover Dam, so does not get captured for human use so much.
Within the Great Basin, which contains Death Valley and other sub-basins as mentioned, any rainfall will never run to the ocean, but instead gets used by humans, evaporates, or just soaks into the ground locally. There are a number of dry lake beds around the Great Basin where they may fill by a few inches during a storm or over a wet season, only to dry-up later, leaving increasingly dense deposits of minerals and salts. These salt flats end-up as good places for testing jet cars, aircraft, or storing UFOs.
Several years ago, when Texas had some terrible flooding, I inquired here about whether the water could possibly drain into old oil wells, and in time replenish the aquifer. People here who know their stuff said that wells are almost always capped, and for the ones that aren’t, the water would be too polluted to use anyway, so in short, most of it would sink into the ground.
Rainwater allowed to “sink into the ground” is the ideal situation. Water is naturally filtered when it passes through soil, and then it replenishes the ground water to be used by other municipalities.
Many storm drain systems include large retention basins which allow runoff to collect and sink into the ground.
The problems arise when there is simply too great a volume. The ground reaches a saturation point where it will hold no more water. This is the type of flooding we are seeing in the Eastern states.
Perhaps all of the Plains states can be utilized as a gigantic wind farm. The energy from this will collect the excess water of the East and pump it to the drought-plagued West!
This natural filtering works well for removing particulate matter from the water. But I’m not so sure how that works for removing dissolved minerals or contaminants or other liquids (like oil) that may be mixed with the water.
Contaminates are handled at the well. Some contaminates cannot be removed, and the well will be decommissioned.
A retention basin constructed to hold storm runoff isn’t intended to do anything other than holding the water and allowing it to percolate down to replenish the ground water.
As more and more construction occurs, the retention basins are almost the only opportunity to keep rainwater as a freshwater source.
Back in the 1980s, William Marshall wrote a remarkable series of police procedurals set in what was then still-British-controlled Hong Kong. At the start of each, he reminded readers that the Chinese owned the water sources and could turn them off at any moment.
Actually, desert areas can absorb quite a bit of water from rainstorms. Even the considerable runoff is not wasted.
“The rain that does reach the desert floor in a summer thunderstorm typically does so with great vigor. Although the dry desert can absorb substantial amounts of water, much of the rain rolls off the hard-baked ground. Sheets of water wash across the land, filling arroyos and riverbeds in minutes, the flow carrying along sand, rocks, and plants, carving new stream channels and eroding stream banks. This runoff is a critical resource for desert life, whether it is providing a temporary pool for a desert spadefoot (Scaphiopus spp.), a cool spell and source of groundwater recharge for urban desert dwellers, or irrigation for a Tohono O’odham squash field.”
