HomeOwners for Better Building - Pennsylvania homeowner flooding problem

Flood problems arise when it rains
Stormwater runoff, and the flooding and erosion it creates, is as serious a threat to homeowners and the county's environmental eco-system as one can imagine. One report called it "the most pervasive problem within Chester County's watersheds."...the folks who live near Inniscrone development in London Grove. Or the 750 residents of Glen Hardie condominiums in Tredyffrin. They are all people whose homes and lives have been - or could be - upended by the runoff that occurs after a storm. "Every time it rained, the water would come barrelling down from upstream," remembers Megan Gelb, an East Caln resident who lives near Ludwig's Run. "It scoured out the soil around the roots holding these huge trees. The trees would drop (into the stream) and take a huge quantity of ground with it."

"Little drops of water ... make the mighty ocean," wrote the 19th-century poet Julia Carney. It's a refrain that children have been comforted by for years as their mothers sang them off to sleep.

But don't try to tell that to Donald and Lucy Schroth of Downingtown.

Or East Caln's Don Wilson. Or the folks who live near Inniscrone development in London Grove. Or the 750 residents of Glen Hardie condominiums in Tredyffrin.

They are all people whose homes and lives have been - or could be - upended by the runoff that occurs after a storm.

"Every time it rained, the water would come barrelling down from upstream," remembers Megan Gelb, an East Caln resident who lives near Ludwig's Run. "It scoured out the soil around the roots holding these huge trees. The trees would drop (into the stream) and take a huge quantity of ground with it."

Gelb estimated that the stream that was eroding the hill that their house was sitting on had created a cliff 14 feet high from the stream bed to their lawn.

Stormwater runoff, and the flooding and erosion it creates, is as serious a threat to homeowners and the county's environmental eco-system as one can imagine. One report called it "the most pervasive problem within Chester County's watersheds."

And yet little is known by the public at large about how stormwater runoff is managed in the county, or what the prospects are for the controlling its damages.

Over the next three days, the Daily Local News will take an exhaustive look at stormwater and its impact here. This special series includes interviews with environmental experts, county water officials and the residents whose lives have been affected by stormwater damage.

Forty years ago, as the earliest subdivisions started to spring up, there wasn't any thought given to stormwater management, said Robert Traver, a professor at Villanova University and director of the Villanova Urban Stormwater Partnership, an organization dedicated to advancing the evolving science of stormwater management.

"It wasn't called stormwater. It was called drainage." As more houses were built and there was an increase in impervious surfaces such as new streets and lawns, flooding started to occur. Detention basins were built to control flooding - to hold the water from large storms and allow it to empty at a slower pace.

Stormwater management has been a subject of considerable research and study, and it was quickly recognized that the original design of detention basins had two serious flaws.

The first flaw was that while the outflow pipe on the basin was much smaller than the inflow pipe, during a storm there are hundreds of basins all over the county releasing water at the same time.

In East Whiteland and Tredyffrin, 165 basins were surveyed during a study of the Valley Creek watershed. All those basins emptying into streams at the same time cause the water level in the stream to rise rapidly, which contributes to downstream flooding -- exactly what the basins were designed to prevent.

Every township has its stormwater problems, whether it's flooding from small streams that turn into raging cataracts when it rains, or poor stormwater management from older subdivisions. Every municipality has to allocate resources to try to correct stormwater problems.

Stormwater runoff was recognized as a serious threat by the county's integrated water resources plan, "Watersheds." Adopted in 2002, the report notes "stormwater runoff is the most pervasive problem within Chester County's watersheds."

The cost to control the problem can be great. For example, Downingtown is spending $2 million to replace a bridge and is building a $1 million detention basin to manage stormwater from surrounding areas that ends up in the borough.

It can cost hundreds of thousands of dollars to restore streams whose banks have been eroded by the action of rushing stormwater, as was shown in Uwchlan recently where sections of Shamona Creek underwent costly repairs. One resident who lives along the creek complained that they used to be able to jump across the creek and now it's 20 feet across in some sections.

The Chester County Conservation District cobbled together $300,000 to repair a section of Ludwig's Run that was threatening the home of one Norwood Road resident.

Many Downingtown residents live in fear when it rains.

Donald Schroth is afraid to travel in case there is a flood when he is gone. Other people who live along streams have the same fears.

The six days of rain that occurred last June created a quantity of stormwater that any municipality would have trouble managing, even without the increased stormwater due to a highly-developed watershed.

Caln's storm drains are sized for a 25-year flood and were quickly overwhelmed when it received the equivalent rainfall of a 100-year storm in one day.

Handling stormwater is a major and ongoing task for public works and township managers. It's a major concern for planning commissions who have to make sure that new land development plans don't add to anyone else's stormwater woes. Once a development is built, if the stormwater infrastructure wasn't designed properly, it frequently becomes the problem of the municipality.

While there isn't much that anyone can do about the vagaries of Mother Nature, trying to manage increased stormwater as a result of more houses, parking lots and lawns is something that municipalities have to cope with.

The U.S. Army Corps of Engineers' report in 2003 regarding flooding in Downingtown pointed the finger at one cause for increased flooding.

"The surge in new home construction over the last decade has resulted in a significant increase in stormwater runoff," the report said. The runoff is not only from increased development in the borough but from the hills surrounding Downingtown.

The Army Corps estimated the Parke Run sub-basin to be 14 percent impervious surface, such as pavement, concrete, rooftops, etc. Generally when impervious surfaces cover less than 10 percent of the land used, the watershed functions well. Watersheds with more than 20 percent of the land area covered with impervious surface often show patterns of a degraded watershed.

Flooding problems from small rainstorms have increased due to changes in land use and ineffective stormwater management, notes a manual from the state Department of Environmental Protection (DEP). The additional flooding is the result of an increased volume of stormwater being discharged, which is a direct result of the increase in impervious surfaces.

In the past, before the land was converted to housing developments, the forest could handle average rainfalls. Forests can soak up or evaporate 95 percent of precipitation. Big storms came through once in a while and caused streams to overflow and downstream residents to be flooded.

But more development has led to more houses, parking lots and suburban lawns. The runoff has not traditionally been managed well, and results in more frequent flooding and erosion of stream banks. Streams can become stormwater channels laden with sediment from eroded stream banks that suffocate invertebrates. Runoff warmed by hot asphalt can increase water temperatures and kill cold water species such as native brown trout.

Under natural woodland and meadow conditions, only a small portion of rainfall becomes runoff. Mix in development, however, and the situation changes.

In a simplified illustration of the problem in DEP's manual, only eight inches of the 45 inches of annual rainfall on a one-acre wooded lot would become stormwater runoff.

In contrast, an acre of developed land which includes a building, a parking lot and lawn generates 43 inches of runoff. The house and parking lot are impervious surfaces and the lawn which has been regraded and compacted is nearly impervious. Very little water can infiltrate most suburban lawns. Heavy construction equipment can compact soil so significantly that lawn soil approaches the bulk density of concrete, according to DEP.

Forested woodlands do a good job of managing stormwater. The roots of the tree hold water. The leaves and bark of the tree allow for evaporation and absorption. Leaf clutter on the forest floor and loose soils hold and store rainwater and allow it to percolate slowly into the water table.

Of the 45 inches that fall annually on a one-acre forested parcel, about half evaporates back into the atmosphere and about 15 inches infiltrate to the water table.

Tomorrow: How a light rain becomes a flood.
To contact staff writer Anne Pickering, send an e-mail to This e-mail address is being protected from spam bots, you need JavaScript enabled to view it