Rock Weir

In season, which is April through October, weather permitting, we do a lot of maintenance throughout Headwaters Park.  Much of it is routine, such as keeping trails free of obstacles, making sure trails are clearly marked, managing poison ivy, and the like.  Occasionally we get the opportunity to use information about conservation and preservation to create cool educational demonstrations for the public.  It also gives us an opportunity to play in the stream and woods:)

Recently, on a routine check of our bridges, we discovered our main bridge over Mill Creek needed attention.  A supporting post had begun to sink into the streambed and needed to be readjusted and given additional support.  Using a handyman's jack, we were able to raise the bridge several inches to a level height.  After we finished the steps for the undersupport, we began creating outer support with limestone rocks. 

They are heavy.  Very heavy.

Through use of a wheelbarrow, sledge, and old-fashioned arm strength, we maneuvered the rocks to appropriate spots on the streambank, which were then positioned along the bridge support according to size.  The biggest rocks were placed first, followed by medium sizes, and the final rocks, the smallest, were used for filling in the small holes and niches.  The difference in the bridge is noticeable, and we were thankful for a beautiful work day to complete the project. 

We had been watching the banks of Mill Creek near the bridge for a time, checking on the level of erosion.  When the water is lower, as in the summer, the amount of soil from the banks washing away is very low.  However, when we have a significant rain storm, or a snowmelt in the spring, one can almost watch the soil and sediment being washed from the banks, eroding quickly.  In the area by the bridge, one can see the exposed roots from the nearby Eastern Hemlock tree, uncovered by soil erosion.

In an effort to conserve our land resources, we built a rock weir in the stream.  A rock weir is one of many BMPs, or Best Management Practices.  These BMPs are used to help keep our waterways and land as clean and healthy as possible.  The rock weir is used to guide water flowing downstream to the middle of the stream, rather than having water rocket off the side of the stream bank and creating erosion.

Although the rock weir may resemble a pile of rocks for kids to play with in the water, they are actually placed very carefully to guide the stream flow to the middle.  The weir is lowest in the middle, to allow for easier passage of water.  The sides are built up out of the water, guiding the water toward the middle.  The sides are also rounded to point downstream. 

Physics Experiment!:  Create a flow of water with a hose, or find a stream.  Using a log or branch, lay it down in three different positions:

• From the bank to the middle of the stream, with the bank end upstream
• From the bank to the middle of the stream, straight in
• From the bank to the middle of the stream, with the bank end downstream

Watch the flow of water after the log settles.  The water likes to flow 90 degrees, straight down over the log.  So, in creating a weir to guide water to the middle of the stream, the sides of the weir need to point...?  Cool, huh?

We are in the monitoring stage of our weir.  There has not been much rain throughout the region in months, so it is currently difficult to gauge the efficiency of our weir.  However, calibrations will be made as necessary when we do see that big storm or have that spring snow melt!

Answer to the Monarch question:  Female - do you know why?