It's Not Just the Rain!
According to the United States Geological Survey, groundwater provides about 40% of our public water supply and an additional 40 million people get their drinking water from wells.
Groundwater is not only an important source of drinking water in every state - groundwater levels are important to people who rely on surface water, too. This is because, on average, about half of the flow in a river comes from underground sources. With precipitation and river levels below average across much of the country, it's worth considering why the amount of water bubbling up into our rivers, lakes, and reservoirs may be dropping, too.
"Impervious Surfaces" and Groundwater Recharge
"Impervious surfaces" such as roads, parking lots, and roofs associated with sprawling urban development significantly change natural river flow patterns and the recharge of underground water supplies.
Rainfall cannot soak into the ground through these surfaces and thus does not replenish groundwater supplies. Impervious surfaces also increase the amount and speed of water entering rivers and other water bodies.
The result is an increase in the severity and frequency of floods, the displacement and destruction of habitat for fish and other water dependent species, and a decrease in base flows in our streams and water in our aquifers.
How Sprawl Affects Our Water Resources
Loss of Natural Areas
Loss of wetlands, forests and meadows has many negative impacts, among them, the loss of the enormous water storage capacity of natural areas.
A one-acre parking lot will cause the runoff of 16 times more rainfall than an acre of undeveloped meadow, whereas an acre of wetlands can store 1-1.5 million gallons of water
Small streams are the capillaries of our freshwater systems. They collect rainwater, and slow its movement downstream to larger streams. When the water table is low, they actually recharge groundwater as well.
But sprawling development fills or buries as many as 1/3 of our small streams in underground pipes to make way for buildings, roads, and parking lots. Much of the rain that used to be caught and held by these small streams now runs off and is lost to rivers and lakes in urbanized areas.
Sprawling low-density development is a leading cause of imperviousness, with automobile-related surfaces such as roads and parking lots accounting for 50 to 66% of the total imperious surface in cities! Much of the impervious surface is in excess to actual need -- commercial parking lots have vacancy rates that are frequently as high as 60-70%. One study from Iowa City, Iowa found that even the highest occupancy rate, which was in the 10 days before Christmas, was only 74%, and it averaged only 36% other times
Sprawl means more than roads and parking lots, it also means larger and larger lots planted with turf grass -- which are often nearly as impervious as concrete and asphalt Suburban "estate" properties consume as much as 16 times more water than homes in the urban core on smaller lots. On average, a full 58% of our residential water use is for outdoor purposes such as landscaping, and per capita use is about 50% higher in the arid West than the East.
Water infrastructure associated with sprawl development -- such as storm drains and culverts -- treats precipitation as something to dispose of rather than something to protect. This infrastructure channels rainfall and snowmelt into storm drains and pipes, and dumps it into receiving waters, often far from its place of origin. The consequences are the loss of groundwater recharge, reduced base flows in streams, increased flooding, and lower water quality.
What Can Be Done?
- The most important thing local governments can do is to promote cluster development to leave large areas of native vegetation and small streams intact.
- Residents and businesses can replace lawns with native vegetation, and collect rainwater from roofs to store for irrigation or discharge downspouts into local infiltration fields, not storm sewers.
- Local governments can limit impervious surfaces - limiting roads and parking lots and requiring construction using permeable surfaces where appropriate.
- Local government can reconfigure traditional stormwater infrastructure to increase infiltration. Seattle, WA, reduced runoff by 97% the year after converting an open ditch stormwater drain to an attractive roadside swale garden, decreasing the width of the adjacent street and planting native vegetation.
- Oregon's Museum of Science and Industry re-designed its parking lots to minimize stormwater runoff and maximize local infiltration of rainwater. OMSI's parking lot now has capacity to infiltrate almost .5 inches of rainfall every time it rains, and construction costs fell $78,000!