The Town of New Hartford has initiated engineering studies to provide guidelines for beach sand replenishment at Brodie Park. The initiative is two part – better understand the causes (and opportunities for mitigation) of the erosion of beach sand into the lake, then define best management practices for beach sand replenishment.
Evident in the photo below, considerable amounts of sand wash under the silt fences and into the lake. The impact has been a need to annually replace sand. Replacing beach sand is expensive. Correcting drainage above the beach and therefore minimizing beach sand erosion could mean saving money and eliminating one more source of unwanted silt and sediments in our lake. Prevention of erosion should come before adding more sand.
[captionpix imgsrc=”https://westhillpond.org/wp-content/uploads/2014/04/photo-1-2.jpg” captiontext=”Beach Erosion at Brodie Park”]
But there are also other benefits. At a recent New Hartford Wetland Commission’s hearing to review the proposed Best Management Practices (BMP), a community member brought the three “beach” samples shown below. The left sample (mason’s sand) is similar to what has been place on the beach likely for decades. The center sample meets, in fact exceeds, the specification in the proposed BMP, the right sample is 3/8 inch washed gravel similar to the material recently placed at Sequassen. One-quarter cup samples of each of three different samples were added to a quart Mason Jar of West Hill Pond water. The results speak for themselves. Protecting the water quality of West Hill Pond demands keeping silt – from any source – out of the lake.
[captionpix imgsrc=”https://westhillpond.org/wp-content/uploads/2014/04/BeachMaterials_after12hourssettling.jpg” width=”480″ alt=”Sample Beach Materials” captiontext=”Samples of three possible beach materials after approximately 12 hours settling”]
[captionpix imgsrc=”https://westhillpond.org/wp-content/uploads/2014/04/BeachSand_36hours.jpg” width=”480″ alt=”Sample Beach Materials” captiontext=”Same samples after approximately 36 hours settling”]
[captionpix imgsrc=”https://westhillpond.org/wp-content/uploads/2014/04/BeachSand_60hours.jpg” width=”480″ alt=”Sample Beach Materials” captiontext=”Same samples after approximately 60 hours (2½ days) settling”]
The proposed BMP specification would allow 3% of the “sand” to pass a #200 sieve – which is the smallest sieve size in the testing. That #200 sieve has openings that pass a .075″ particle (~1900 microns). Particles that pass through a #200 sieve are typically called silt under most engineering scales (Wentworth, USDA, ASTM, AASHTO, etc.). The simple math says that out of 30 tons of sand, the specification allows up to 1 ton of what would be referred to as silt. According to Stoke’s Law, silt above 100 microns is considered “settleable” but below that, the particles remain in suspension as shown in the sample photos. But even those particles larger than 100 microns may take days or hours to settle.
[captionpix imgsrc=”https://westhillpond.org/wp-content/uploads/2014/04/ParticleSize.png” width=”480″ alt=”Particle Sizes” captiontext=”Graph of particle sizes (courtesy UCONN Engineering)”]
As rainwater and snowmelt run over the beach they pickup this silt, it goes into suspension in the lake, and can be transported significant distances. The smallest/lightest particles are the last to settle, and thus the first to be stirred up by aquatic animals, humans or even wind fetch induced currents or the annual temperature induced turnover. Reduced clarity correlates to reduced visibility, and a reduction in disinfection of pathogens by ultraviolet light and in studied cases, increases in presence of microbial pathogens. Why does the sand require replacement? Conjecture is that a considerable amount of the sand washes into the lake through erosion of the type shown in the above photo.
Most residents are aware that Wetlands Regulations specifically prohibit placing any material in the lake without express authorization. Under permit, Connecticut Yankee Council’s Camp Sequassen is experimenting with using small (3/8″) pre-washed gravel – of the type shown in the mason jar on right – for one of their waterfront activity areas. This is the same size material found on the exotic beaches of Mediterranean Europe … notably Corsica. The results are not yet in, but Ranger Dave Boyajian says “It looks nice and I walk around on it in bare feet. It wasn’t bad to me!” Perhaps Brodie Park can experiment with an area of this material to gather resident feedback and better inform its users about the potential impact associated with decades of beach sand containing silt.
If you would like us to bring this demonstration to any meeting of one of the WHPA Member Organizations please reach out to Skip Sly.