By Jim Northrop, GSWA Member
In Bound Brook, New Jersey, there was a flood in 1996, and in 1999 Hurricane Floyd brought 17 feet of water to downtown Bound Brook. In 2007, there was another flood, followed recently by heavy rainfall which caused more downtown flooding. Some people call these “100-year floods,” but they all occurred over a mere 15 years. How can we have several “100-year” floods in the short span of 15 years?
Some people mistakenly believe that a “100-year” storm or “100-year” flood happens only once every 100 years. The term “100-year” flood is shorthand for a flood that statistically has a 1% (1/100) chance of occurring in any given year. Likewise, the term “100-year” storm is used to define a rainfall event that statistically has this same 1% chance of occurring this year. For a hydrologist studying water flows, “100-year” means an extreme hydrologic event having a 100-year recurrence interval.
Based on historical data about rainfall and stream stage at a given location, a process of frequency analysis is used to determine the probability that an extreme hydrologic event (such as a river cresting at a flood stage of 20 feet) will be equaled or exceeded in any given year.
Ten or more years of data are required to perform a frequency analysis for the determination of recurrence intervals. Of course, the more years of historical data the better -- a hydrologist will have more confidence for an analysis of a river with 30 years of record than one based on 10 years of record.
Thus, the terms “100-year” storm or “100-year” flood, are used merely to simplify the definition of a storm or flood that statistically has a 1% chance of occurring in any given year. It is not the promise of a 100-year interval.
Showing posts with label Posted by Jim Northrop - GSWA Member. Show all posts
Showing posts with label Posted by Jim Northrop - GSWA Member. Show all posts
Monday, March 22, 2010
Thursday, August 6, 2009
Do Your Homework...
Five years ago when my wife and I were house-hunting in suburban New Jersey, we fell in love with a 6 acre parcel bordered at the rear by a lovely stream. This stream is one of five which feed the Great Swamp, and then become part of the Passaic River. We have really enjoyed watching the seasons come and go along the stream, and one day we even caught a glimpse of a heron.
Last week, I happened upon my neighbor Frank one evening as I walked my dog. The same stream abuts both of our properties, but his house is closer to the water than mine. Importantly, he also has a direct view of a little island in the stream, about the size of a tennis court. The island is rocky and covered with underbrush --- generally it is considered an “eye sore.” Lately, area youngsters seem to have adopted the island, making it their “club house.” In the evenings they often gather after sunset and become disturbingly loud.
The Plan
My neighbor was upset about this island’s physical condition. But he was particularly disturbed by the “attractive nuisance” it represented to the youth who congregate there. He told me of his plan to privately bring in a bulldozer and level the island. He thought it would take less than an afternoon and that he would be making a great contribution to our neighborhood, all at his own expense ---- “it will be my gift,” he said.
As my dog and I continued our walk, I thought about Frank’s plan. I had several questions Frank had not answered. First, whose island was this, anyway? Secondly, I knew that to get a bulldozer into the water, the stream embankment would need to be cut and graded because of the sharp five foot drop-off to the water. Thirdly, did Frank know whether any conservation easements existed to buffer the stream corridor from just the kind of alteration that Frank was proposing? And finally, was destruction of the island the only, or the best, way to correct the problems that Frank saw? Frank liked to call himself “a man of action,” so he had not explored these questions. He said the bulldozer was coming in two days.
Doing Homework May Reveal Some Defects In The Plan
As my dog and I returned home that evening, Frank was still there, weeding a garden. I decided to share my concerns with him, and urged him first to consult with the Township Engineer. While the N.J. Department of Environmental Protection has general jurisdiction over fresh water wet lands and streams, small land use issues may sometimes be handled by local authorities, such as the Town’s Board of Adjustment. The Township Engineer should visit the stream site, I told Frank, and give his opinion about which agency can actually authorize the stream encroachment and give any required permits. I noted that the DEP vigorously enforces the New Jersey land use regulations with severe penalties.
Then we talked about the gathering of youngsters that Frank viewed as a noisy nuisance. “Frank,” I asked, “wouldn’t it be much easier to just ask the police to visit the area around the island periodically and bring order? And, it would not cost you ANYTHING!” Frank smiled and thanked me for the suggestion. He admitted that perhaps he had been a little impulsive, and that his plan of island removal was a bit drastic. We agreed that the Township Engineer probably would have some simple new suggestions for how to make the vegetation on the island less of an “eye sore,” while keeping the island largely the way nature had provided it.
Frank left me wondering just how often busy, well-intending people do not do their homework. This is one reason that not-for-profit environmental organizations like the Great Swamp Watershed Association are such a great resource for citizens facing a land use issue. With one phone call, impetuous Frank could have begun his homework and been sure to avoid some serious mistakes.
Last week, I happened upon my neighbor Frank one evening as I walked my dog. The same stream abuts both of our properties, but his house is closer to the water than mine. Importantly, he also has a direct view of a little island in the stream, about the size of a tennis court. The island is rocky and covered with underbrush --- generally it is considered an “eye sore.” Lately, area youngsters seem to have adopted the island, making it their “club house.” In the evenings they often gather after sunset and become disturbingly loud.
The Plan
My neighbor was upset about this island’s physical condition. But he was particularly disturbed by the “attractive nuisance” it represented to the youth who congregate there. He told me of his plan to privately bring in a bulldozer and level the island. He thought it would take less than an afternoon and that he would be making a great contribution to our neighborhood, all at his own expense ---- “it will be my gift,” he said.
As my dog and I continued our walk, I thought about Frank’s plan. I had several questions Frank had not answered. First, whose island was this, anyway? Secondly, I knew that to get a bulldozer into the water, the stream embankment would need to be cut and graded because of the sharp five foot drop-off to the water. Thirdly, did Frank know whether any conservation easements existed to buffer the stream corridor from just the kind of alteration that Frank was proposing? And finally, was destruction of the island the only, or the best, way to correct the problems that Frank saw? Frank liked to call himself “a man of action,” so he had not explored these questions. He said the bulldozer was coming in two days.
Doing Homework May Reveal Some Defects In The Plan
As my dog and I returned home that evening, Frank was still there, weeding a garden. I decided to share my concerns with him, and urged him first to consult with the Township Engineer. While the N.J. Department of Environmental Protection has general jurisdiction over fresh water wet lands and streams, small land use issues may sometimes be handled by local authorities, such as the Town’s Board of Adjustment. The Township Engineer should visit the stream site, I told Frank, and give his opinion about which agency can actually authorize the stream encroachment and give any required permits. I noted that the DEP vigorously enforces the New Jersey land use regulations with severe penalties.
Then we talked about the gathering of youngsters that Frank viewed as a noisy nuisance. “Frank,” I asked, “wouldn’t it be much easier to just ask the police to visit the area around the island periodically and bring order? And, it would not cost you ANYTHING!” Frank smiled and thanked me for the suggestion. He admitted that perhaps he had been a little impulsive, and that his plan of island removal was a bit drastic. We agreed that the Township Engineer probably would have some simple new suggestions for how to make the vegetation on the island less of an “eye sore,” while keeping the island largely the way nature had provided it.
Frank left me wondering just how often busy, well-intending people do not do their homework. This is one reason that not-for-profit environmental organizations like the Great Swamp Watershed Association are such a great resource for citizens facing a land use issue. With one phone call, impetuous Frank could have begun his homework and been sure to avoid some serious mistakes.
Monday, July 13, 2009
The Largest Great Swamp Creature -- A Concise History
The Great Swamp is home to 32 species of mammals, 21 species of reptiles and 18 species of amphibians -- but all these creatures are dominated by a particular creature category called homo sapiens, or more commonly, humans! Has this been a happy relationship?
How Did It Start?
When European settlers arrived in the Great Swamp area, they found evidence of at least two permanent Lenni Lenape Native American communities. Since then a number of Native American camp sites have been identified near the Great Swamp. Agricultural products, animal skins, herbs for medicinal purposes, and trees for canoe transportation, were obtained from the Swamp by these early inhabitants.
During the first part of the 17th century, the Native Americans were left alone in the area. The Minisink Trail, a significant “Indian trail” in the area, used extensively by the Lenni Lenape, crossed the Swamp’s neighboring town of Chatham.
A Second Wave
By 1664, the territory that would become New Jersey was divided into East Jersey and West Jersey. Certain land in and around the Great Swamp area was acquired at one point by Sir William Penn and his sons. However, it appears that “clear” title passed in 1708 to another group of English investors who purchased the land that included the Great Swamp. It is reported that the Native Americans thought they were granting hunting and fishing rights, but English law was applied, and they lost their land.
By the early 18th century, farms and mills provided the principal occupations, as towns developed around the Swamp, but the population remained light. A devastating fire in the Great Swamp in 1782 following a period of drought, burned for weeks, to the detriment of those dependent upon the Swamp’s resources.
Trades and Professions Replace Farming
Efforts to farm the land in the 19th century were difficult, and despite efforts to drain the area, it remained primarily wetlands and wilderness However, newly established railroad lines from New York City by the end of the 19th century, changed the character of the communities around the area. Residential and professional pursuits began to replace farming, but some of the “small town” feeling remained. When plans for a jetport in the Great Swamp were revealed in 1959, the depth of feeling to preserve this place became apparent and the jetport plan was defeated.
Reportedly, some 250,000 people visit the Great Swamp each year. Residents and visitors continue to hold great power to do good as well as harm in the Great Swamp. Fortunately, the choice made by most affected homo sapiens has been to protect and preserve the Great Swamp. We hope to continue in this direction.
The Great Swamp Watershed Association with some 1600 members and a variety of continuing conservation projects, is one example of how the “largest Great Swamp creature” is benevolent, protecting the natural environment for future “creatures” of the Great Swamp.
How Did It Start?
When European settlers arrived in the Great Swamp area, they found evidence of at least two permanent Lenni Lenape Native American communities. Since then a number of Native American camp sites have been identified near the Great Swamp. Agricultural products, animal skins, herbs for medicinal purposes, and trees for canoe transportation, were obtained from the Swamp by these early inhabitants.
During the first part of the 17th century, the Native Americans were left alone in the area. The Minisink Trail, a significant “Indian trail” in the area, used extensively by the Lenni Lenape, crossed the Swamp’s neighboring town of Chatham.
A Second Wave
By 1664, the territory that would become New Jersey was divided into East Jersey and West Jersey. Certain land in and around the Great Swamp area was acquired at one point by Sir William Penn and his sons. However, it appears that “clear” title passed in 1708 to another group of English investors who purchased the land that included the Great Swamp. It is reported that the Native Americans thought they were granting hunting and fishing rights, but English law was applied, and they lost their land.
By the early 18th century, farms and mills provided the principal occupations, as towns developed around the Swamp, but the population remained light. A devastating fire in the Great Swamp in 1782 following a period of drought, burned for weeks, to the detriment of those dependent upon the Swamp’s resources.
Trades and Professions Replace Farming
Efforts to farm the land in the 19th century were difficult, and despite efforts to drain the area, it remained primarily wetlands and wilderness However, newly established railroad lines from New York City by the end of the 19th century, changed the character of the communities around the area. Residential and professional pursuits began to replace farming, but some of the “small town” feeling remained. When plans for a jetport in the Great Swamp were revealed in 1959, the depth of feeling to preserve this place became apparent and the jetport plan was defeated.
Reportedly, some 250,000 people visit the Great Swamp each year. Residents and visitors continue to hold great power to do good as well as harm in the Great Swamp. Fortunately, the choice made by most affected homo sapiens has been to protect and preserve the Great Swamp. We hope to continue in this direction.
The Great Swamp Watershed Association with some 1600 members and a variety of continuing conservation projects, is one example of how the “largest Great Swamp creature” is benevolent, protecting the natural environment for future “creatures” of the Great Swamp.
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