Tuesday, October 29, 2013

Why erosion control is needed at Hawksnest

Erosion and stormwater are one of the largest sources of nutrients to ponds on Cape Cod.   Stormwater runoff causes the erosion, and also caries nutrient-rich debris to the pond--dog waste, human waste, soil, leaves, and garbage.

Nutrients in turn cause toxic algae blooms, and the growth of aquatic weeds that reduce the quality of swimming and other uses.  Once nutrients get into the lake, they are extremely difficult to eliminate.  The pond is degraded forever.  Alum treatment can improve the lake, but it's expensive and has to be repeated periodically.

Erosion around ponds isn't recognized as a problem, because such erosion is normal for the seacoast.  Most people are familiar with ocean beaches, but the ponds are less visited.  So people think erosion around ponds is normal.  In fact, they probably enjoy the enlarged beaches caused by erosion and trampling of shore vegetation.  But the enlarged beach eventually degrades water quality--the very reason they came to the beach.

The coastal plain ponds of Cape Cod are a rare and threatened ecosystem--totally different from the seacoast.  Ponds are very protected from winds, waves, ice movement, and tides.  So before settlement, the shores were completely clothed with a ring of brushy vegetation.

It's here along the shore that we find species of special concern like the Plymouth gentian and sun dews.  In the shallow water are several endangered species of damsel flies.  The ring of vegetation protects the pond's water quality in several ways...
  • The ring prevents erosion of the shoreline.  When the banks and bluffs along the shore erode, they dump enormous quantities of nutrients into the lake.
  • The ring acts like a screen to catch falling leaves before they reach the pond.
  • The ring acts like a filter to prevent runoff and floating debris from reaching the pond.  
  • The nutrients trapped at the shore feed growth of shrubs with perfumed flowers--rather than growth of toxic algae in the pond.
Everywhere in the USA, people flock to the shores of ponds and streams, trampling the vegetation.  Almost everywhere except in remote places, shoreline vegetation has been destroyed.  So Hawksnest presents a unique laboratory for learning--a unique resource for the schools of Harwich, and for scientists worldwide.

What happens when you don't prevent erosion

Walden Pond, made famous by the writings of Thoreau, has hundreds of thousands of visitors a year.  For many decades, they trampled the shores until severe erosion set in.  The State delayed until finally, about five years ago, they made extensive repairs and restored the vegetation.  These repairs cost over a million dollars.  At Hawksnest, we could do repairs before runaway erosion sets in, for only a few thousand dollars.

At Nickerson State Park, toxic algae blooms have prompted a study, probably leading to treating the pond with alum.  One cause of the algae blooms at Nickerson is the severe erosion of the surrounding bluffs and trails, along with loss of the protective ring of vegetation.

A number of other nearby ponds have experienced algae blooms: Molls, Great, and Herring ponds in Eastham; Long and Cliff ponds in Brewster; along with Hinkley's, Seymour's, John Joseph, Buck’s, Kiddies, Sand, Aunt Renie’s and Skinequit ponds in Harwich.  Long Pond is right next to Hawksnest.  Residents around Skinequit Pond purchased a $45,000 SolarBee to reduce the pollution.

Eroding basins

Undisturbed woodlands on Cape Cod have extremely porous soil.  The water sinks right in.  Streams and gullies normally don't occur.  So before settlement, little debris washed into ponds--and they remained extremely pure.

At Hawksnest before the park, the only way debris could get in was from the air.  I springtime, yellow pollen from the pines made golden rows along the shore.  Leaves blew in during the fall, but only from trees right along the shore.  A little dust came in with the rain.  All this was blown across the lake by southwest winds, and trapped in the little cove over by Spruce Road (what we call the beak of the hawk sitting in Hawksnest).  That's why a little corner of the cove is the only swampy, mucky, weedy place in Hawksnest.

But once erosion started at Hawksnest, water ran more swiftly to the lake over bare, compacted soils.  The fast-moving water began to carve basins.  The dirt roads and trail became tributaries, directing more water towards the pond.

Now the parking lot at the end of Hawksnest has become a bowl-shaped basin that channels water towards trails leading to the lake.  The trail from the parking lot that goes up over the hill is beginning to channel more and more water into the eroding parking lot.   These enlarging basins are channeling more and more dirty water towards the pond.  As they flow, they channel dog and human waste towards the pond.  There are no port-a-potties, and sometimes 25 people come for a party.

So, with increasing erosion, it's fair to say that the area that sheds leaves and dirt to the pond has enlarged from just a tiny ring (the shore protected by vegetation) to many acres--consisting of the trails, roads, and basins that now send runoff to the pond.

The larger these runoff basins become, the faster they erode.  At some point, the erosion becomes "runaway" and very hard to stop.

Stages of erosion
  1. Bare soil.  Vegetation is removed.  Leaf litter is raked or blown away.  Soil is compacted by traffic, so rain cannot sink it.  Instead, if flows over the ground.
  2. Channel formation.  You can see a small channel, marked by signs of flowing water, such as a little "dike" of pine needles that floated to the edge of the channel.  Or, you may see some bare soil, or sand that washed down the channel.  The channel focuses the power of erosion on one spot.
  3. Channel excavation.  The channel starts to deepen into the soil, perhaps exposing a few roots of trees.  The basin starts to enlarge, as soil from the surrounding area is removed.
  4. Many tree roots exposed.  For a while, the roots of trees act as little dams.  They slow the flow, so the water can't pick up too much speed.  The roots hang onto the soil.  But erosion is nearing the runaway point.
  5. Tree roots undermined.  Once the roots are undermined, they can be broken by traffic, or water simply goes under them.  The roots are the last protection--once more than half are gone, runaway erosion can occur.  When many roots are destroyed, the surrounding trees die--increasing the rate of erosion by wind and pounding rain.
  6. Gully formation.  Most erosion occurs only during severe storms, causing people to underestimate the danger.  Nothing much happens for perhaps ten years.  Then a big gully opens up in a storm--but this was perfectly predictable.  Once a gully forms, it becomes nearly impossible to deflect the stormwater, so it continues to erode, unless you fill it in.  And that can be expensive.
Big dogs, horses, bicycles, ATVs, and 4X vehicles make erosion much worse on trails.

The two trails that lead to the pond from Round Cove Rd are at Stage 4-5.  The left-hand trail (facing the pond) trail to the pond from the parking area is at the most risk for runaway erosion, because the slope is steep.  The roots of a big oak at the bottom are becoming undermined.  Runaway erosion could be only one hurricane away.

An opportunity for Harwich

There's still time to fix erosion at Hawksnest inexpensively.  One problem is the paperwork and fees required for a permit from the Conservation Commission.  That would be prohibitive, if a permit has to be applied for, each time we do anything within 100' of the pond.  It's hard to plan ahead, because an erosion problem can develop suddenly.

If Friends of Hawksnest can apply for a permit once--say for a 10 year period--a permit which limits us to certain low-impact techniques at Hawksnest State Park, it would remove a major obstacle--and would facilitate writing grants.  This extended permit might require periodic consultations with the Conservation Agent.

It would also set an example for other Cape ponds and even nationwide, demonstrating that proactive erosion control by volunteers is possible.  Right now, everywhere we're stuck in reactive mode.  The problem is ignored until it becomes severe.  Then everyone wants it solved right away, at great cost.  Here's a chance for Friends of Hawksnest to make an enormous contribution.

Priorities for Round Cove Road beach

Near term (no permit needed)
  • Re-establish barriers to prevent vehicles from approaching close to the pond (in the hollow).
  • Replace any silt socks that have broken.
  • Close the trail over the hill (that feeds runoff into the parking area).  This will be very hard to do, until the Friends gain community support for this.
  • Obtain a necessary specific or general permits.
  • Reinforcement of the gully from the hollow to the beach.
  • Restoration of the hollow, plant pine trees near the shore, filling of giant puddle.
  • Shoring up of the bottom of the steep trail, to protect the roots there.  Deflection of water from the trail.
  • A port-a-potty.
  • Close the current parking area, and restore the eroding basin to make it a picnic area.  This steep area simply isn't appropriate for parking.  Establish parking instead at the bottom of the hill, south of Round Cove Rd.
  • Build boardwalks allowing access to the beach from the parking and picnic areas, so that people don't erode the trail.
  • A gate, to be closed by local residents at park closing time. The gate could also be closed during rainy weather.  This would allow restoration of the road.  If the road is not closed when wet, then any improvements will quickly be destroyed.
Priorities for the Walker Road landing

This area has a plan developed by the State, and approved by the Conservation Commission.  It would cost tens of thousands of dollars to implement, and so hasn't been done.  Instead, volunteers could prevent erosion here, with minimal expense.

The main problem here is runoff coming down the eroding access road.  It flows directly into the pond, frequently washing ashes and garbage from campfires into the pond.  This water can be deflected away from the pond by building a berm with a rake--but traffic keeps destroying the berm.

Near term
  • Build a low berm.  Maintain it frequently.  Remove any blockage that prevents runoff from flowing away from the pond.
  • Establish a fence to keep dogs and people away from the bank on the left, near the pond.   Cover with mulch and plant native shrubs.
  • Dig some trenches high on the road to deflect water from the road.
  • Get a permit from the Conservation Commission.
  • Build a permanent berm from gravel to deflect runoff from the pond.
  • More permanent shoring up of the water's edge, possibly including the posts called for in the State's plan.
  • Possibly improve the road or parking on this side.  This side is really more accessible than the Round Cove side.  Any road improvements would be shorter.
  • A gate, to be closed by local residents at park closing time.
  • A port-a-potty.
Other shores of the pond

In 2011, a new access point down a steep slope on the north shore was opened by a person walking dogs.  There is potential for erosion.  This area needs to be watched to see if it is healing.

The Water Quality Task Force reports "Runoff-From Rt 6 and Spruce Rd, Storm drains discharge onto West Shore."   Investigate.

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