When you drive around West Windsor or Plainsboro you can’t go very far without going over one of those small highway bridges where the road crosses a small stream or river. In most cases the identity of the waterway is not given on a sign, so it’s easy to see why so few people know what or where it is. But they do exist and they have been here for a very long time. They have been important factors in where the water goes when we have a big storm — or even a small one, if it comes around often enough.

Natural waterways form over time as a result of how stormwater drains from the land on which it falls to land at a lower elevation nearby. That’s just a matter of gravity. But there are many other factors that affect the details of where the water goes. The topography of the land, the type of soil, its porosity, and its distribution, the presence of vegetation such as trees and planted crops, and the prevailing moisture content are all factors that affect where the water goes and at what rate.

Perhaps most importantly, the way the land has been used by the human population since farming began is a key factor. When you plant crops in a field that was once a forest, you can change everything.

Together West Windsor and Plainsboro contain 14 named waterways. In West Windsor they are Bear Creek, Canoe Brook, Little Bear Brook, Big Bear Brook, Duck Pond Run, Hixon Run, Bridegroom Run, and Assunpink Creek. Plainsboro has Cranbury Brook, Shallow Brook, Devil’s Brook, Bee Brook, and Cedar Brook.

Common to both townships is the Millstone River. It forms the entire border between West Windsor and Plainsboro. With few exceptions, all the listed waterways in both townships empty into the Millstone and their water eventually reaches Raritan Bay to the northeast. The exceptions include Hixon Run, Bridegroom Run, and Assunpink Creek, all of which ultimately end up in the Delaware River to the west of our “continental divide,” the last two via Lake Mercer in Mercer County Park.

An additional waterway that is common to both townships is the Delaware and Raritan Canal, a man-made waterway that can receive substantial runoff during storms, but which plays a minor role in draining this area. Since the canal is not a natural waterway, its water is confined to a man-made channel that is independent of the natural waterways near it.

Where it intersects the course of a natural waterway, such as the Millstone river, its water is confined to a wooden and concrete channel, or aqueduct, that allows the water of the natural river to flow beneath it. One West Windsor stream, Duck Pond Run, empties directly into the canal near Princeton Country Club. The effect of the Millstone River blockage due to the aqueduct is not substantial. (For more on the aqueduct, see “Looking Back,” November 8, 2013.)

The Millstone itself is a slow-moving river because it traverses such flat territory. Water in the Millstone and the Raritan, into which the Millstone flows, travels about 30 miles from the canal aqueduct before reaching sea level in Raritan Bay. Near the aqueduct its lowest embankments are about 40 feet above sea level. Thus its flow due to gravity is sustained by an average elevation drop-off of about 16 inches per mile, which is not much.

When it comes to why storm water goes where it does, there are several other factors in addition to the natural ones mentioned above. All of these are the product of how the land is developed and used. For both townships almost all the open land had been used for farming for a very long time. Only since around 1900 has there been a gradual change, and in the past 50 years that change has definitely not been gradual.

The rate at which land absorbs storm water depends on many factors including the type of soil on top and the underlying material. Sandy soils and those dominated by clay or organic material all absorb or reject moisture differently, so it isn’t possible to generalize about water runoff from different areas.

Land that is paved with impervious cover as on roads and driveways drains into a system of storm drains. Over the years both West Windsor and Plainsboro have developed very effective systems of leading the runoff water to final drainage locations that help minimize its contribution to flooding. But again, when flooding does occur the main cause is the flat terrain and the relative lack of natural waterways that can drain different areas naturally.

Getting back to some of the waterways, especially the lesser known ones: In West Windsor how many people could find Canoe Brook without a map, unless, of course, they live on Canoe Brook Drive in Colonial Park? It probably doesn’t even show by name on many maps of the area.

Well, Canoe Brook is an element in one of the most important and symbolic places in the whole township. The overflow water from the Twin Ponds 9-11 Memorial at the Rogers Arboretum flows into Canoe Brook and then through the woods north of the arboretum on its way to Grovers Mill Pond — after passing under North Mill Road. Canoe Brook rises west of Penn-Lyle Road, skirts the south and east boundaries of the grounds of High School South, and flows under Hightstown Road and Hendrickson Drive near the tennis courts.

How about Bridegroom Run? It starts in East Windsor and goes under South Lane, Old Trenton Road, and Edinburg Road on its way to Lake Mercer. There are bridges at all three crossings, but you have to know what you’re looking for to notice them. Frequently when you see a weight-limit sign on the road, it refers to an upcoming bridge that may be all but invisible when you reach it.

Hixon Run is another stream probably known only to those who live near it. It runs north of and parallel to Village Road West near the Windsor Ponds development and crosses under Quaker Bridge Road into Lawrence Township close to the railroad main line. You’ll never see it unless you go hiking in the woods.

Whenever we experience a sustained heavy rainfall that is sufficient to cause local flooding, there is usually much public comment about why the township can’t do something to prevent it. In responding to such concerns, it must first be realized that — as the old saying goes — we have to play with the hand we’ve been dealt. We live in a very flat area where drainage is slow to begin with. Add to that the fact that we have permitted a huge amount of our land to be covered with impervious substances and houses, then we have brought the flooding on ourselves by changing the way much of our land is used.

In my more than five decades in West Windsor what I consider severe flooding has occurred about once every decade, usually coinciding with strong tropical storms. By severe flooding I mean roads becoming impassable at several locations simultaneously and remaining that way for several days.

Temporary road closings of a day or less at one or two isolated spots may be inconvenient, but, to me, are by no means a cause for great concern — they go with the territory. When that happens find another way of going where you want to. Short of creating a mountain range in our flat terrain and rerouting our streams and rivers, we’re stuck with what we have, and no amount of innovative engineering will change that.

Both townships have developed effective systems of coping with stormwater and ways to minimize flooding. Engineering studies have been done, and overall plans such as development of the West Windsor Greenbelt plan and its execution have been very effective in coping with heavy rains to minimize flooding. Preservation of open space through the efforts of FOWWOS (Friends of West Windsor Open Space) and the development of the Mercer County Park have also helped substantially.