Lake Condition Updates

September 16, 2016

A delay in the availability of the dredging equipment has caused the dredging of the forebay to be pushed back several weeks to the end of October.  

Dragonfly Pond Works will use pump dredging to remove enough silt from the forebay to achieve an average water depth of 3.5 ft.  It expects to remove approximately 150 tons (175 cubic yards) of silt from the forebay.  The silt will be pumped into geotextile fabric dewatering bags located in the low area adjacent to the east edge of the forebay.  (These areas often flood during heavy rain events.)  It will be allowed to dry for about eight weeks after which time the bags will be opened and the dried silt spread on site and then stabilized with vegetation.

Dragonfly has had good results with this technique in FL. Although Dragonfly has not used this dredging technique in NC, it expects it to work well based on its performance in FL and the results that a competitor had dredging a pond in Cary NC. .

A video showing the equipment in use and information on the performance specifications of the equipment can be found at www.dinosix.com.   


August 28, 2016

Meritage Homes received dredging plans from Edge Environmental and Dragonfly Pond Works (DPW).  It decided to award the contract to DPW.  DPW’s pump-dredging approach allows them to remove the silt (sediment) without draining the forebay.  (In pump dredging the silt is sucked up by a nozzle held against it and sent into water-permeable membrane bags which let the water drain out but hold the solids.)   DPW plans to locate the permeable bags in low areas adjacent to the forebay.  These areas often flood during heavy rain events.  After the water has permeated out of the bags, DPW will open the bags, use the dried solids to fill-in these low areas and then stabilize the fill dirt with vegetation cover. DPW expects to do the dredging in early October.  


July 30, 2016

Bill Mitchell talked with Meritage Homes' dredging contractor yesterday afternoon.  The contractor said that he was still developing the dredging plan, and he could not set a date for the dredging until after Meritage Homes and Parkwood approve the plan. 


July 29, 2016

Note:
In the July issue of the Inside/Out, the word "not" was left out of the last sentence in the 6th paragraph (Update.) It should have read "...the buildup of sediment has not been as much as suspected".


Status Report on Dredging the Lake Forebay (Lotus Pond)

 

Background (See July 2016 update below for More Information)

Stormwater runoff from the Meadows at Southpoint development north of Parkwood has been sending colloidal clay (micron-size clay particles that don’t settle out by gravity) and larger clay particles into our Lake’s forebay (particle retention pond) and the Lake itself  for more than a year.  About eight months ago a small island of mud broke the surface of the forebay and increased in size noticeably in less than three months.  The presence of this island and its rapid growth indicated that the ability of the forebay to prevent particles from reaching the lake was being challenged. 

 Meritage Homes, the developer, has agreed to work with us to dredge any significant sediment buildup in the forebay and the Lake.  Under the agreement, Parkwood’s lake and pond maintenance contractor (Dragonfly Pond Works) is to determine the water and sediment depths across the forebay and also the area where water from the forebay enters the Lake (bathymetric survey).  Meritage Homes’ contractor (Edge Environmental) will then use the bathymetric data to develop a dredging plan; obtain all of the necessary equipment and environmental permits, drain and dredge the forebay and dispose of the dredged material. Dragonfly will also assist Edge Environmental in developing the plan (if requested) and review the plan.

Update:

Dragonfly Pond Works conducted the bathymetric survey on July 12, 2016 and sent the results to Edge Environmental on July 22, 2016.  The bathymetric survey showed that the buildup of sediment has not been as much as suspected.  Here is a summary of the findings:
 
  • The water depth is still over 3 feet in 70% of the forebay.
  • There is no sediment buildup in the Lake (so it will not have to be dredged).
  • About 30% of the forebay has less than 6 inches of sediment buildup.
  • About 35% of the forebay has between 1 and 4 feet of sediment (the area in and around the mud island and the point where the water enters the forebay).
  • The remaining 30% or so has between 6 inches and 1 foot of sediment.
Edge Environmental is now using the distribution of the sediment and the information on the quantity that will need to be dredged to complete the dredging plan and cost estimate for submittal and approval by Meritage Homes.  The goal to complete the dredging by the end of July 2016 was not met.  A new date has not been set.


July 2, 2016

Status Report on Dredging the Lake Forebay (Lotus Pond)

Once Meritage Homes began to actively develop the Meadows at Southpoint site in the spring of 2015, storm water runoff from the site carried submicron-sized clay particles (colloidal clay) into the Parkwood Lake and the particle retention pond immediately upstream of the lake (the lake forebay). These particles turned the water a deep cream-with-coffee color. 

 

Colloidal clay particles can stay suspended in water for months before they become large enough (through agglomeration) to settle out because of gravity.  For a number of reasons (e.g., there is no reliable, cost-effective control technology available, the total weight of clay actually released is small, etc.), the USEPA and the state do not regulate colloidal clay releases. (One milligram of these particles produces about the same color change as 1,000 mg of silt particles suspended in the same volume of water.)

 

When we made Meritage Homes aware of the impact their runoff was having on our water bodies, they worked with us to try to reduce the amount of colloidal clay entering our water bodies but nothing worked.  About seven months ago a small island of mud broke the surface of the forebay and increased in size noticeably in less than three months.  Although agglomerated colloidal clay particles probably contributed to the formation of this island, silt particles released from the Meritage Homes development site were likely the primary source. But we have no way to prove this.

 

The presence of this island and its rapid growth indicated that the ability of the forebay to prevent particles from reaching the lake was being challenged.  So, in March Jacob Ehrisman and I met with Lawrence Lane (Raleigh Division President) and Brian Ketchem (Environmental Coordinator) of Meritage Homes. When we showed them photos of the muddy island, they offered (as a good neighbor gesture only) to dredge the Lotus pond at their expense. They also agreed to involve our lake and pond maintenance contractor (Dragonfly Pond Works) in the planning and implementation of the dredging. 

 

After a number of unsuccessful attempts to get together with Meritage Homes, Tom Pullaro of Dragonfly Pond and I finally met with Brian Ketchem and the Meritage Homes’ dredging contractor (Edge Environmental) at the forebay on June 21, 2016.  We worked out a tentative schedule for the dredging and assigned responsibilities for its planning and implementation.  Edge Environmental will develop the first draft of the dredging plan; obtain all of the necessary equipment and environmental permits, drain and dredge the forebay and dispose of the dredged material.  Dragonfly Pond will do a water depth profile on the forebay and determine the amount of sediment to be removed. They will also assist Edge Environmental in developing the plan (if requested) and review the plan. The goal is to complete the dredging by the end of July 2016.

 

I will post updates on the Parkwood Association website (parkwoodnc.org) as the project progresses and also provide monthly updates in the InsideOUT on the dredging project and our related efforts to monitor, assess and address the impact of the clay releases on our water bodies.

 

Bill Mitchell, Chair

Parks, Lawn and Ball field Committee

Comments