Sunday, July 10, 2011

Big rainstorm pollutes NW side of Hawksnest Pond

On Friday, morning, heavy rain pummelled Harwich while I was showing Selectman Larry Ballantine around.  It was the most intense storm in over a year, and we both were soaked to the skin.  But the pond took the worst beating.

Selectman Larry Ballantine enjoys a drenching at Hawksnest.
The black material under his feet includes campfire ashes and forest debris.

For several years, I've been warning of the threat of erosion at Hawksnest, and trying to fix the problems at the two landings.  But on Friday, Larry and I had a chance to see the problem "live."

Because ponds in Cape Cod are fed by pure groundwater seeping through the sand, most have exceptional water quality, compared to the rest of the country.  And Hawksnest has the best water quality of any pond in Harwich.  The pond is pristine because there are no houses with septic systems nearby, and because the shoreline is nearly 100% intact--totally vegetated.  This intact ring of natural vegetation at Hawknest is truly extraordinary--it could be an example for the whole nation.

Because of the protective shore vegetation, not a drop of water gets into Hawksnest unless if falls on the surface or seeps through miles of sand.  Unless bare areas like roads or parking lots feed stormwater to the pond through gullies.

Over the past decades, parking areas near Hawksnest have expanded.  They have become eroding basins, growing larger each year, feeding gullies that run to the pond.  When it rains, these three gullies can carry tons of debris, animal waste, and soil to the pond.  Because this waste contains nutrients (fertilizer), it can and will eventually create toxic algae blooms in the pond.

Last summer, I restored a "monster puddle" at the Round Cover area that had become a cesspool of waste.  It was within 8 inches (elevation) of breaking through to the pond.  I also laid "silt socks" to slow runoff, and divert it away from the pond (and the puddle).

Most of this work was successful, so when the storm came Friday, only a little debris went into the Pond from the Round Cove parking.

"Delta" at the bottom of gully near Round Cove Parking.  Most of the runoff was diverted from this gully.  Nevertheless, the pond bottom near the beach still has a thin layer of muddy sediment.

Closeup underwater view of bottom, near the above photo.  A thin layer of dark sediment is visible--it washed in with the small amount of runoff here.

But on the Walker Road side, things were different.  I had created a low berm of sand, to direct runoff coming down the road away from the pond.  But so much runoff came down the road that it breached my dam, and went straight into the pond.

As I swam around the pond on Saturday (half a day after the rain ended), I encountered a lot of floating debris just west of the entrance to the cove.  By the time I reached the landing at the Walker Rd side, the water was quite muddy, stirred up by eight people swimming.  I have never before seen this amount of dirt in the water.  It was spread all along the western side of the pond.

Underwater view at Walker Landing.  Much more debris was washed in here.  When swimmers enter, they stir up this sediment, making the water muddy.

The water here still smelled OK, because the debris was simply dirty sand, pine needles, and other forest debris.  But this kind of debris contains a lot of nutrients.  Bacteria in the pond will break it down into real fertilizer, which eventually will stimulate an algae bloom.  When this happens, the pond becomes unbalanced, and will be much less appealing for swimmers and fishermen.  Ponds which contain too many nutrients do eventually start to stink.

To see the future of Hawksnest if we don't control the erosion and nutrients, just look at neighboring Black Pond.  Yesterday, Irwin Schorr told me there used to be a turkey farm next to Black Pond, on the west near Walker Rd.  Turkey waste is great fertilizer--probably the biggest reason that Black Pond is a mess today.  How many times have you taken a dip in Black Pond?

By Sunday, a day and a half after the rain ended, the pond off Walker landing was still black on the bottom with debris.  But on the Round Cove side, the thin layer of fine black sediment had dispersed. 

At the landing east of Round Cove parking, at the end of a long path, there was no runoff from the storm at all.  There is no erosion in this area, and the intact vegetation completely protected the pond.  There was no debris in the pond at all, and the sand on the bottom was almost pure white (below).

S shore of Hawksnest, E beach access.  No erosion here.
This is the way the shore should look after a heavy rain.

Hawksnest Pond, if it remains protected, is of great value as a natural laboratory.  It can show the rest of the country how best to manage lakes and ponds.  After the storm, the contrasts in water quality between the protected shores and the eroding shores at Hawksnest were stark.

The lessons are clear:  The pond--and it's protective ring of plants--is very fragile.  Protect the shore vegetation and prevent erosion, and your grandchildren can enjoy the pond you love, just as you do today.
But neglect shore protection--and you'll have two Black Ponds to swim in.

Yes, erosion is "natural," in the sense that water responds to gravity, and flows downhill.  But erosion around Cape Cod ponds almost never occurred before settlement, and it isn't desirable.  Hurricanes and tornadoes are "natural" too.

The ponds on Cape Cod are called coastal plain ponds.  They are a rare and endangered resource.  They are an environment protected from extremes of wind and waves (and the erosion they cause).

In contrast, the ocean coasts normally experience much erosion--but the vast ocean is capable of dealing with the debris and nutrients that wash in.

So if you want to have campfires or do wheelies in the parking lots at Hawksnest, take your fun to the ocean beach, which isn't so fragile.

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