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While watering our gardens and lawns during the past summer's drought, our main focus was to keep the plants alive in the blazing heat. But after water-use restrictions were put in place throughout the Delaware Valley, our thoughts also turned to the water systems beyond the end of the hose. Some of us looked no further than the nearest well or reservoir, but these are just the man-made "taps" into larger natural systems of water storage and recharge, called watersheds.
The History of Philadelphia's Watersheds and Sewers
Compiled by Adam Levine
Philadelphia Water Department
All of us live in one watershed or another, determined by the stream into which the stormwater from our property drains. Even an urban rowhouse dweller far from any above-ground stream lives in a watershed; chances are, in Philadelphia, at least, that the nearest creek runs underneath the street, now captured in a sewer pipe. A watershed for a small tributary creek can cover just a few acres, whereas the Delaware River watershed, encompassing hundreds of smaller watersheds, covers more than 12,000 square miles.
The State of Our Watersheds
Healthy watersheds replenish and purify our water supply and provide a home for many plants and animals. Unfortunately, most of the watersheds in the Delaware Valley have been badly compromised over the years. Rapid and poorly planned development, the increasing acreage of water-resistant lawns and pavement, pollution from various sources, and many other human activities all have taken their cumulative toll on water quality and quantity, as well as wildlife diversity.
"In the last century we have disrupted--more than probably any other natural system--the patterns of water to which plant and animal communities have adapted over millennia," writes Leslie Jones Sauer in The Once and Future Forest. "A discontinuous patchwork of deteriorating pipes, ditches, channels, impoundments, and wells has replaced and significantly dismantled the natural infrastructure of streams, wetlands and aquifers, which have been filled, drained, diverted, channeled, pumped, and dammed."
The good news is that just as human activities have degraded our watersheds, a different set of activities can help to restore them. Since most watersheds include a number of municipalities, regional planning that goes beyond a piecemeal approach is a crucial part of this recovery process. Instead of an ill-conceived patchwork of town-by-town plans, broadening the planning process to include a survey of water resources before going ahead with development will help protect critical areas such as wetlands and flood plains, allocate water resources according to various needs, and limit development to a level that the watershed can reasonably sustain.
On a smaller scale, individuals can also play a crucial role in watershed preservation. "Even if there is no stream in sight, your land is a piece of a watershed's puzzle," states a brochure on watershed stewardship published by the Chester County (PA) Water Resources Authority. We can get involved in the local planning process, and help local watershed groups with their stream cleanup and restoration projects. Most important, we can learn more about our own little pieces of the "puzzle," and how what we do in our gardens can have effects far beyond our property lines, for better or worse.
In an undisturbed watershed, the groundwater level and stream flow--while fluctuating according to the season and amount of rainfall--maintain themselves within a normal range. Because the stream bank and channel change over time, streams end up following the familiar meandering pattern that flowing water establishes even in the tiniest rivulets. The flood plain and wetlands along the stream corridor absorb the occasional high waters and support a variety of wildlife unique to such an area.
Few watersheds today are undisturbed. In general, the higher the population density, the greater the disturbance. Many areas, built up beyond the capacity of their water resources, pump more water out of underground storage reservoirs, or aquifers, than is flowing into them. In some places groundwater levels are so low that, instead of feeding streams as they normally do, they now suck water out of them. During dry spells in the summer, the flow of water in many streams, including the Wissahickon Creek in Philadelphia and Montgomery counties, consists mostly of the discharge from upstream sewage treatment plants.
Large areas of a watershed, including flood plains and wetlands, may also be "impervious," covered by surfaces through which water cannot penetrate: paved streets and parking lots, house and building roofs, and, surprisingly, lawns. A slightly sloping area of mown grass will deflect almost as much stormwater as pavement. Where 80% of the water in an undisturbed watershed infiltrates into the groundwater, in many developed areas the same amount runs off on the surface, thereby decreasing the recharge of groundwater supplies. This means that more stormwater now reaches streams more quickly, and in greater quantity. More runoff makes a stream more prone to flash flooding even in relatively minor storms. Filling and building on flood plains and wetlands, as well as creating embankments to channel the stream and keep it from spilling out over its banks, only serve to increase flooding downstream of these "improvements."
Higher storm flows can have many effects. They erode stream banks more quickly and deeply, disturbing native plant populations and creating openings for invasive exotic plants, such as Japanese knotweed. Erosion increases the amount of sediment in the stream, eventually eliminating the gravely areas in which a number of desirable fish, such as brook trout, prefer to feed and breed. In steep stream valleys, what would naturally be shallow tributaries can become deeply gouged gullies, further increasing sediment levels downstream and opening up more ground for invasive plants.
Twenty or more years ago, most stream pollution came from pipesfrom factories and sewage treatment plants emitting foul effluent directly into waterways. But as those "point" pollution sources have been forced to meet stricter Federal guidelines, the majority of stream pollution, in both developed and agricultural watersheds, now comes from widely dispersed, difficult to control "non-point" sources.
During heavy rains, stormwater scours the streets and landscape and carries many non-point pollutants directly into streams, including gasoline, motor oil, lawn chemicals, and dog waste. In rural areas, runoff from farmlands can contain high levels of livestock manure, fertilizer and pesticides. Water percolating through the ground is purified somewhat, since microorganisms in the soil break down various pollutants. But since most stormwater runs off the surface, it doesn't get a chance to benefit from this natural, biological process.
Non-point pollution is one of the most serious challenges to the health of our streams today, and is the one area where the cumulative effect of individual actions can be significant. Every time we put something on or in our landlawn fertilizer, pesticides, motor oil dumped behind the garage or down the storm sewerwe are contributing to non-point pollution. Many storm sewers empty directly into the nearest stream, yet people still use these streetside inlets to dump motor oil, paint, solvents, and other hazardous materials.
Even when dumped "behind the garage," these substances can still make their way into groundwater supplies. Pouring them down the drain isn't the solution, either. In areas with combined sewer systems, the pipes carry both sewage and stormwater to a sewage treatment plant during dry weather. But during heavy rains, when the volume of flow is too much for the treatment plant to handle, excess stormwater along with diluted sewage is discharged directly into waterways. Most counties have "Household Hazardous Waste" collection days; contact your local Health Department for information about the next day in your area.
"Reducing the extent of lawn is one of the easiest and most effective ways of addressing stormwater management while increasing the area of potential wildlife habitat," writes Leslie Jones Sauer. "Letting some of our lawn area grow up into meadow allows water to percolate into the ground instead of running off. It also means that you'll be using less fertilizer and pesticides, which can wash off a lawn during heavy rains."
Here are some other lawn tips to help save our watersheds. If you are fortunate enough to live by a stream or pond, don't mow right up to the edge of the water. Leave an unmowed buffer, the wider the better, and preferably planted with trees and shrubs, which encourage even more infiltration than meadow grasses. Another way to decrease runoff is to redirect downspouts away from paved areas and onto lawns or wooded areas. Rain barrels can also be used to store water, for use on the garden between rainstorms.
The Big Picture
The main point is that each of us needs to get to know our local watershed. Janet Bowers, executive director of the Chester County Water Resources Authority, encourages people to learn about their watershed and pay a visit to the nearest accessible stream. "Walk in it, wade in it, canoe, take pictures, or go fishing," Bowers says. "It's important that we touch the water and play in it." "You might not want to drink it," Bowers cautions. "But we need to stay connected to streams and understand their vitality and importance. If we lose that connection and become apathetic, that's when decisions are made that will take it away from us."
Adam Levine lives by Vernon Run, a tributary to Ridley Creek, in Rose Valley, Pennsylvania. Besides the sources quoted above, he would like to thank Ann Smith and Mark McGuigan of the Pennsylvania Environmental Council, Nancy Goldenberg of the Natural Lands Restoration & Environmental Education Program, Blaine Bonham of the Pennsylvania Horticultural Society, and Nancy Crickman of the Department of Environmental Protection for providing background information used in the preparation of this article.