What I saw was an immense rainwater harvesting system! The catchment area supporting the Colorado River includes seven states and collects the rain and snow melt in its watershed. A roof is a catchment area and can be viewed as the watershed for your rainwater harvesting system. A roof has slopes and valleys and sheds water into gutters and downspouts. The Colorado River Watershed therefore catches rain and snow fall and then focuses the runoff down the slopes and canyons to the river. The river, like a gutter, moves the water to the collection system. The Hoover Dam created Lake Mead or the reservoir that collects and stores the water. In a rainwater harvesting system the reservoir is created by an above or below ground tank. One of the issues with all dam projects is the problem of silt. The river carries silt which is deposited behind the dam and builds up over time. Silt will reduce the storage capacity of the dam and limit its life. A rainwater harvesting system can also capture organic solids that flow off your roof, but because the size and scale is so much smaller, excellent ways of filtering debris have been created to reduce or eliminate the debris from entering the rainwater harvesting tank. It is very important to screen the debris from entering the tank for several reasons. Organic material in a closed container can breakdown and significantly reduce the water quality over time. Typically, when you want to use the water to irrigate your property, debris in the system may clog or ruin a pump or clog emitters in a drip line and therefore reduce irrigation performance. In the case of dam projects there is no simple way to screen out silt or debris as there is in rainwater harvesting projects. Another aspect of the Hoover Dam are the overflow spillways on each side that protect the reservoir from overflowing the dam itself. When the water in Lake Mead rises to a certain level it begins to overflow and is released downstream. Similarly in a rainwater harvesting system the tank fills and also flows through an overflow when it reaches its maximum capacity. The overflow water can be sent into the yard and passively used in bioswales to infiltrate into the soil and improve its moisture content. The Hoover Dam also uses four intake towers to direct water to the turbines at the bottom of the dam to generate power. The water is then released back into the Colorado River and flows downstream. A rainwater harvesting system also has one or more methods of distribution on the tank. A spigot can be installed to allow the water to flow via gravity based on the pressure built up by the height of the water in the tank. Or a pump can be installed to receive the water and pressurize it for a larger irrigation system or whole house water system. Once the water is used either for non-potable or potable uses it can then be sent on passively into the soil or as gray water or black water and processed appropriately.
So, as I was standing on the new interstate bypass bridge being buffeted by 50 mph winds and taking pictures it also gave me pause to recognize the immensity of this project, what an engineering and construction marvel it is, and allowed me to compare how this project was similar in many ways to a rainwater harvesting system. If you ever have the chance to visit the Hoover Dam, do it! And if you have the chance to build a rainwater harvesting system I would be glad to help you design and install it!