As meteorologists monitor the El Nino condition currently gaining strength in the Pacific Ocean, Californians look with hope to the much-needed rain and snow it could yield. But if we're going to make the most of the precipitation, we need to put a LID on it. LIDs, or low-impact development technologies, mimic pre-urban stream functions. Examples are green roofs that absorb and evapotranspire rainfall; rainwater tanks attached to homes and other buildings; and permeable pavement for roads, driveways and parking lots. Rainwater could even be used in the home for toilet flushing and laundry. Managing stormwater runoff in urban environments is a challenge for engineers and water officials. During pre-industrial times, rainwater gradually seeped into the ground and, from there, into rivers, lakes and oceans. Humans, however, have replaced forests and grasslands with a lot of impermeable surfaces that send runoff in a torrent directly to the closest waterways. Symptoms include erosion, flooding and rising stream temperatures; an imbalance in nutrients, carbon and oxygen in the water; and an increase in unwanted sediments, chemical pollutants and human pathogens.
