Gateshead Detention Basin. This detention basin is designed to reduce the
runoff from the development during small, frequent storms which otherwise could cause
erosion. It is part of the Washington Valley Storm Water Control System. Major flood
control is provided at the Washington Valley Reservoir. Civil engineers refer to storms by
their return periods. A return period is a rather confusing concept. Since storms are
statistically random events, it is easiest to think of storms in terms of their
probability, or chance, of occurring. For example a flood with a one rear return period
(known as a one-year flood) would have a 100 percent chance of occurring in a given year.
Other return periods, probabilities, and rainfalls are shown below:
Therefore as shown in the table above, there is a fifty percent chance that a two-year
storm will occur this year, but only a one percent chance of a 100-year storm.
The high frequency storms can cause more erosion over time than the big floods, since
there will be about 100 one year storms of about one third the size as the single hundred
year storm in the same period. This is why detention basins in the Washington Valley area
are often sized to control only the smaller storms while developers contributed money to
fund flood control constructed by Somerset County at the reservoir. Flood control and
erosion control are provided separately. In most areas there is no overall plan for storm
water control and detention basins provide for both functions. This can lead to higher
maintenance costs and unforeseen problems if all the basins discharging into the same
brook peak at the same time. Part of this flood control plan requires keeping development
further away from the stream then usual. This helped to create the park that includes this
trail.
Do you have detention?
Why build detention basins such as this one? Just imagine the water running off this
development after a typical summer downpour: Detention basins slow the waters progress,
stopping erosion and catching pollutants such as surface oils and grease from reaching
nearby streams. Small frequent storms can often cause more erosion problems than big flood
events such as hurricane Floyd, which happen only rarely.
Detention basins can be great wetland wildlife sites too, but they can also become areas
filled with unwanted invasive plants. The 4’ tall stems of Purple loosestrife are
common in this area. Purple loosestrife can spread easily in the disturbed soil and
changed water flows around detention basins.
Runoff from major storm events is dealt with in part by flood control measures partially
funded by the developers at the Washington Valley reservoir, and by providing natural
buffers along stream banks.
The bridge over the outlet from the detention basin is the second of John Evancho’s
bridges.
