I want to follow up on Howard Eldridge’s interesting and informative letter (The News, May 30) regarding floods from Little Bear Brook. As has been said, those who do not learn from history are doomed to repeat it.
The Irene-Lee event of late August, 2011, was indeed historic. Photos taken by several West Windsor residents on August 28 show that it was a “500-year” flood as judged from the respective limits shown on official FEMA maps and charts. Little Bear Brook rose past Rush Holt’s office on Route 571 all the way to the corner of Alexander Road and Vaughn Drive.
Farther downstream, the Millstone River overtopped Route 1 near Harrison Street, closing this major artery and doing substantial damage in that area. This must have been due to the Millstone not being able to effectively empty into Carnegie Lake. Either the lake was too high, or there were restrictions at the confluence, or both. Backwater effects resulted, and several West Windsor residents reported that Little Bear Brook, which runs into the Millstone, was flowing backwards at times.
Flood information about Mercer County streams can be found by Googling the term “Mercer County fis maps.” Clicking on the first site that comes up will retrieve Volume 1 of the Mercer County Flood Insurance Study (Preliminary, May 30, 2013), which gives explanatory material.
Detailed flood profile charts are in alphabetical order in Volumes 2 and 3. The URL for Volume 2 is floodmaps.fema.gov/prelim/PrelimData/New Jersey/Mercer Coun-ty/prelim_issue_date-2013-05-30/FIS Reports/34021CV002A.pdf.
(For Volume 3, substitute 003 for 002 near the end of the url.) The Little Bear Brook chart is on Panel 74P of Volume 2 and the Millstone River charts are on Panels 78P through 84P of Volume 3.
These charts have notations showing places where the various streams cross roads and other landmarks. They show predicted water levels resulting from events having probabilities in any one year of 10 percent, 2 percent, 1 percent, and 0.2 percent respectively (i.e. “10-year, 50-year, 100-year, and 500-year” floods). The Little Bear Brook chart also states that throughout its length there is a 1 percent annual chance of backwater effects from the Millstone. In other words, with a 100-year or worse flood, Little Bear Brook will run backwards.
The Millstone chart shows that to flood Route 1, the water level in that stream (which together with Stony Brook forms Carnegie Lake after the Millstone goes under the canal) would have to have been at least 62.5 feet at that point. (All elevations here are per the newer NAVD88 basis. In our area, the newer basis is one foot lower than the older basis.)
At the confluence of Little Bear Brook with the Millstone, the high-water level would have been about 63.5 feet (or higher) at that point according to the charts when it was 62.5 feet (or higher) at Route 1. This likely was the main reason that Little Bear Brook could not drain effectively. Photographs show that it reached levels of about 63 feet on Route 571 and at the intersection of Alexander and Vaughn. The latter elevations can be determined to one-foot accuracy by going to the site called “The National Map,” zeroing in on our area, and using the “spot elevation” tool.
Given the high water level in the Millstone, it is no wonder that Little Bear Brook flooded the way it did then and still continues to do after heavy rains. Though it would obviously help somewhat to remove any partial obstructions currently existing in the brook’s channel, as Mr. Eldridge mentions, this would not address the other major problems inherent in the Millstone and Carnegie Lake proper. These problems likely could only be solved by major engineering projects, with due consideration for the effects these would have on communities farther downstream that already flood after major storms.
John A. Church
West Windsor
Howard Eldridge is correct in his letter in the May 30 issue. Lake Carnegie plays no part in the flooding of Washington Road caused by Little Bear Brook. Both it and its companion waterway, Big Bear Brook, enter the Millstone River quite some distance before the Millstone gets to the aqueduct of the D&R Canal under which it flows prior to reaching Carnegie.
Only during the heaviest, sustained downpours can the lake’s elevation play a role in causing a backup of the Millstone from that point and subsequent problems upstream in areas of West Windsor and Plainsboro, but not as far as Washington Road. That was not the situation in our recent flooding episode, anyway — which was quite minor compared to the “big ones” we have every 15 or 20 years or so.
The main problem with Little Bear Brook where it passes below Washington Road is that the terrain throughout its course is very flat. In fact, depending on where the heaviest rain was, part of it used to sometimes flow in the opposite direction, away from Washington Road until it joined Duck Pond Run. The modifications made during the development of Windsor Haven and the Estates at Princeton Junction have had a positive effect in this regard. Cleaning out the blockage in the water course should help.
Dick Snedeker
West Windsor
