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If you live in Brown Township, you are quite familiar with the term "ponding." In the eastern half of the township, the land is so flat that after heavy rains, temporary ponds develop in just about every field. Here are a few pictures of ponding in our area:
We understand that this ponding occurs, and we prepare for it. But we also count on our neighbors to control the flow of stormwater from their properties. It is unacceptable for a landowner to change the profile of their land to cause stormwater to run off onto a neighbor's property. These ponds disappear on their own, sometimes in hours, in other cases over several days, depending on the amount of rainfall we receive. A great deal of water is simply absorbed into the ground. Some of the rest is captured in drainage tiles which carry the water to a nearby drainage ditch, or a creek. In the area between Alton Darby Rd and Walker Rd, we count on Hamilton Run to carry the excess water away. Hamilton Run is a small creek, and when a great deal of rainfall occurs, it rises and flows at greater velocity. Why doesn't all this extra water cause flooding downstream (Hellbranch, Big Darby, Scioto River?). The answer is that it can and sometimes does. A key to controlling that flooding is the existence of broad flat areas alongside the creeks that provide places for the creeks to overflow their banks harmlessly and absorb the excess water. These areas are called floodplains. When floodplains are filled in (read about the Homewood episode) it is very much like building a wall along the banks of a creek. Because the excess water has no place to go, the surface level of the creek rises and the water velocity increases. At best this adds to the downstream flooding and bank erosion. But what often happens is that the people downstream decide to build levies to prevent the flooding in their area, and the water levels and velocities just keep getting higher and faster. This is what cause the Mississippi levies to fail in the great floods of the last decade. When Hilliard builds a high school, it replaces acres and acres of absorbent soils with hard surfaces such as buildings and parking lots. All that water has to be moved somewhere. We can be sure that the site plan will call for retention ponds to catch the excess runoff from the buildings and asphalt surfaces. But the construction will also subtly alter the grade of the whole property. Water that used to stand and be absorbed will then run off into the creeks and ditches, potentially displacing that water to the neighbors' property. If this school gets built, those of us who live around it will be very observant about how the stormwater drainage is managed. |
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