As you all have seen, the culvert replacement on South Kingston Road is almost complete.

As of this writing the last concrete is laid and paving begins soon.

After the bridge deck is ready, the bypass road can be dismantled and the final section of culvert and corrugated metal pipe extending the culvert through the bypass road will be removed. Then something stunning will begin. The water level of the slough (or some call it the estuary) will change dramatically.

I (and maybe you too) have walked down to the water’s edge on the Apple Tree Cove side of the new bridge structure and have become aware of some amazing things.

First, as you look south under and through the existing small portion of the culvert and the corrugated pipe, you see how perched the slough estuary has been. “Perched” means it is held artificially above or disconnected from the natural water level. With the culvert, the slough was about 3 feet higher than sea level. Thus, the full ebb and flow of the water with Apple Tree Cove was not possible. It also means the water velocity in the slough was artificially slowed, causing faster deposition of more fine material than would occur with a more natural open-water connection.

The new, wider bridge connection will make pretty dramatic changes in the water level in the slough.  If you think of the whole tidally influenced slough/estuary, which extends into the beautiful portions of waterway you view from West Kingston Road (connecting with the salt marsh and the Carpenter Creek watershed), the water levels in the whole estuary area at high tides will also be lower. This entire estuary area will naturally fill and drain, restoring the system to more variable affects of tidal fluctuations.

Water will now rush through a wider under-bridge connection changing its speed and trajectory.  The wider area has already significantly changed Apple Tree Cove north of the culvert. Its change in water velocity will change its capacity to carry sediment and nutrients. We already see these effects! As you may remember from other articles, we reported on the fish we counted in the scour hole north (cove side) of the culvert. It was a deep hole where fish and other creatures congregated. This scour hole was created by the rapid, narrowly focused flow of water out of the culvert. That hole has mostly filled in!

The new pattern of water movement created by the wider path under the bridge is modifying banks on either side of the opening.  That water is sculpting a new terrain!

We will be watching nature’s forces change the landscape as we watch the new water levels, stream channels and shoreline outlines form.   Take a look on either side of you (driving safely, of course) every time you go over the new bridge and see what has changed!