trinity lake - draft management plan · trash, litter, and debris 8 aquatic vegetation 9 sediment...

Trinity Lake:

Lake Management Plan

Prepared for: Trinity Lake Homeowners’ Association

Prepared by: Ron Small, Reedy Fork Environmental

December 31, 2010

Reedy Fork Environmental PO Box 10375

Greensboro, NC 27404

Lake Management Plan: Trinity Lake 2



phone: 336.558.5970 • email: [email protected] • www.reedyfork.net

Index Introduction and Background 3 Current Accomplishments 3 Management Plan 3 Earthen Dam 4 Drain Pipe and Valve 5 Principal Spillway and Weir 6 Inlet Channels 7 Trash, Litter, and Debris 8 Aquatic Vegetation 9 Sediment Accumulation 10 Lake Buffer 11 Fisheries Management 12 Additional Resources 13





Introduction and Background Trinity Lake (aka Aydelette Lake) is a 13-acre recreational lake, which was originally constructed in the 1930s. The lake is located on a tributary to Little Alamance Creek, and is impounded by a high-hazard earthen dam (as classified by the State of North Carolina). The lake is arguably the central focus and most-valuable amenity to the Trinity Lake Community, but also presents a source of liability and upkeep. Therefore, we believe it prudent and responsible to develop a thorough lake management plan for Trinity Lake, which should benefit the entire Community. This document can, and should, evolve over time to meet the changing needs and interests of the Community. Ongoing discussions with the Homeowners’ Association and property manager should identify immediate issues and concerns, develop both short and long-term goals for the lake, and consider an appropriate maintenance plan based on the Community’s needs and budget. This current plan was developed after initial research of surrounding properties/land use/drainage area, review of existing surveys and engineering documents, review of prior inspection reports from the State of North Carolina, our own professional experience, and onsite visits and inspections of Trinity Lake. The professional management of Trinity Lake should include a comprehensive and long-term approach. Care and future upgrades of the earthen dam, inspection of seepage, maintenance of trash and debris, management of the fish population, control of algae and aquatic vegetation, future dredging, recreational activities, and aesthetic considerations should all be taken into account together for the benefit of the entire Community. Current Accomplishments In May 2010, the Trinity Lake Homeowners’ Association contracted with Reedy Fork Environmental (Reedy Fork) to provide professional lake management services (inspection, consulting, and maintenance). This service is intended to help the Community maintain the function, safety, and aesthetics of the lake, while minimizing surprise, unscheduled, and unbudgeted maintenance repairs. In 2010, Reedy Fork conducted three, quarterly, onsite inspections and clean-ups of the lake and its component structures. Complete inspection reports, supporting photos, maps, and documentation were submitted to the Community. As a result of these inspections and clean-ups, it is our opinion that trash, litter, and debris are now at a more manageable level, undesirable vegetation has been properly cleared and mowed (and is now being maintained) around the dam area, and the Community is much more aware of the current and future issues surrounding the lake (sediment accumulation, seepage, dam repair, drain valve operation, etc.). Reedy Fork also provided additional investigation and consulting services related to low-flow conditions to the lake, and has submitted several proposals to the Community for future lake management services. Management Plan This document is organized according to the separate structures of the lake (e.g. earthen dam) and the important issues that impact the lake and its surroundings (e.g. trash, litter, and debris). We have included a brief narrative, description of any problems or concerns, and our own recommendations for the Community to consider. We have included representative photos of each structure and activity. Our recommendations are classified as either immediate, short-term, and/or long-term suggestions, primarily based on their perceived importance and costs. Immediate generally refers to 1-3 years, short-term refers to 3-10 years, and long-term refers to 10+ years.





Earthen Dam Trinity Lake is impounded by an earthen, high-hazard dam. The dam is classified as high-hazard by the State of North Carolina due to its height, size of the lake that it impounds, and the risk for property damage and loss of life downstream if the dam were to fail. The need for proper ongoing inspection and maintenance of the entire dam structure is therefore imperative. The entire dam structure consists of the upstream slope (facing the lake), top, downstream slope (facing Young’s Mill Rd.), toe and abutment contacts (where the downstream slope meets the ground below), drain pipe/valve, principal spillway, and weir. For this document, we will discuss the drain pipe/valve, principal spillway, and weir as separate items.

Any future structural repairs to the earthen dam will require prior approval from the State of North Carolina under the NC Dam Safety Law of 1967. The Community would need to retain the services of a North Carolina-registered professional engineer (PE) experienced in dam design and repairs to prepare plans and submit to the State for approval. Due to the age and design of Trinity Lake’s dam structure, it is our opinion that any request for structure repair to the dam, no matter how small, will result in the State requiring a full upgrade of the dam to meet current design and safety standards. Recommendations (immediate):

• Continue ongoing, periodic inspections of the dam to provide an early detection of any cracks, leaks, animal burrows, sloughing, excess seepage, etc.

• Continue to mow and keep the dam clear of all woody vegetation (a healthy stand of grass should be encouraged). We prefer that the grass height never exceed 6-12 inches.

• Identify an appropriate professional engineer to investigate the future steps and costs of upgrading and re-constructing the dam to meet current design and safety standards.

Recommendations (short-term):

• Solicit ballpark cost estimates for future re-construction of the dam. • Establish a long-term budget for future re-construction of the dam based on those estimates. A

project of this scale could easily cost over $300,000, depending on a variety of factors. Recommendations (long-term):

• Re-construct the dam to meet current design and safety standards.





Drain Pipe and Valve The bottom drain pipe and valve for Trinity Lake consists of an 8-inch pipe connected to two hydrant valves. The drain pipe originates underwater in the lake, and is likely buried under the bottom sediment. The pipe runs through the earthen dam, and exits at the toe contact on the downstream slope of the dam.

An operational drain pipe and valve is necessary in the event that the water in the lake needs to be drawn down for maintenance, construction, or investigation. Although we suggest that the drain valve be tested and operated at least once a year, it is currently unknown whether or not the drain valve is operational (or has ever been). The State of North Carolina requires that the drain valve be in good operating condition, as this is a critical component of the high-hazard dam and function of the lake. Until recently, the area around the drain valve assembly has been overgrown with trees, vines, and other vegetation. This area, like the rest of the dam, should continue to remain clear of all woody vegetation, as the roots from this vegetation can cause extensive damage within the pipe and valve. There is a substantial amount of “wetness” and seepage evident around the drain valve assembly. This seepage could be originating from within the dam, groundwater seep, or from a leak in the drain pipe and/or valve. Excessive seepage can cause failure of the dam due to internal erosion and/or embankment sliding. Recommendations (immediate):

• Investigate the area around the drain valve assembly for the source of wetness/seepage. • Test the operation of the drain valve. • Continue to mow and keep the area around the drain valve clear of all woody vegetation.

Recommendations (short-term and long-term):

• Schedule an annual test of the drain valve to keep it in good operating condition.





Principal Spillway and Weir Water exiting Trinity Lake through the dam structure flows through a principal spillway, which in this case consists of a large channel constructed around the south side of the earthen dam. This spillway acts as both the primary spillway (transports normal flow) and emergency spillway (transports heavy storm flows). This spillway channel should always remain clear of trash, logs, debris, etc. so that flow is never backed-up or impeded. The water level (elevation) of the lake is controlled by a stone/brick/block/concrete wall, or weir, at the downstream end of the spillway channel. The weir is approximately 12-18 inches tall, and appears to have been hand-laid at some point years ago. A small, 6-inch drain pipe is positioned through the weir in order to relieve pressure on the weir and to maintain minimum flow downstream.

Based on our observations, there are several small cracks or leaks in the weir, caused by missing stones, damaged grout, etc. The State of North Carolina considers the weir to be a part of the overall dam structure, and repairs to the weir are not allowed without prior approval by the State. As with the earthen dam itself, due to the age and design of Trinity Lake’s principal spillway and weir, it is our opinion that any request for structure repair to these areas, no matter how small, will result in the State requiring a full upgrade of the dam to meet current design and safety standards. Because the weir was constructed on top of a large, stable bedrock outcrop, a complete breach or failure of the weir would simply lower the lake level (elevation) approximately 12-18 inches. The elevation of the stable bedrock outcrop would then act to control the water level in the lake. Recommendations (immediate, short-term, and long-term):

• Continue ongoing, periodic inspections of the principal spillway channel and weir to provide an early detection of any worsening cracks, leaks, animal burrows, etc.

• Continue to mow and keep the banks clear of woody vegetation around the principal spillway channel.

• Continue to remove accumulated trash, logs, and debris from the principal spillway channel and weir.





Inlet Channels Within the Trinity Lake Community, stormwater runoff from homes, driveways, roads, and parking lots flows into a series of approximately 100 curb inlets along the street and discharges into the lake through concrete pipes at 11 individual locations.

Each concrete inlet pipe and channel is designed to have a stable, clean rip-rap (rock) pad between the mouth of the pipe and the lake. This rip-rap pad, also referred to as an “energy dissipator”, acts to filter out large trash, sediment, and other debris, as well as to prevent erosion due to the flow of stormwater. Over time (as designed), the rip-rap will fill up and clog with sediment and lose its effectiveness. Many, if not all, of these rip-rap pads leading to Trinity Lake are clogged with sediment, absent, lacking proper rip-rap, and/or eroded.

Recommendations (immediate):

• Evaluate costs associated with correcting erosion, removing accumulated sediment, and re-installing proper rip-rap pads at all 11 locations per original engineering design.

Recommendations (short-term and long-term):

• Correct erosion, remove accumulated sediment, and re-install proper rip-rap pads at all 11

locations per original engineering design.





Trash, Litter, and Debris Trinity Lake acts similarly to a very large stormwater detention pond, capturing runoff from the Trinity Lake Community, as well as many neighborhoods, roads, and land uses outside of the Community. Unlike a spring-fed pond, Trinity Lake is fed by multiple streams and land covering an area bordered by Young’s Mill Rd. to the east, E. Lee St. to the south and west, and Sharpe Rd. and I-40/85 to the north. That is an area of almost 1,000 acres. The continuous input of trash, litter, sediment, leaves, grass clippings, excess nutrients, and other debris, trapped and filtered out into Trinity Lake, will be an ongoing maintenance concern.

Specifically, trash and litter create an eyesore for the lake, contribute pollutants to the water, and provide ideal mosquito-breeding habitat. Initial clean-up efforts in 2010 removed steel drums, tires, pallets, toys, fishing lures and line, countless plastic bottles/glass bottles/aluminum cans, and other miscellaneous trash from in and around the immediate perimeter of the lake. It is clear from our observations that much of the trash and litter is unfortunately originating from within the Trinity Lake Community.

Recommendations (immediate, short-term, and long-term):

• Continue routine and periodic trash clean-ups in and around the immediate perimeter of the lake. • Consider educational efforts directed at residents to inform them of the consequence of littering in

the Community, or allowing trash and litter to enter the lake. • Install “drain markers” on all stormwater curb inlets, to remind residents not to litter or allow other

pollutants to enter the storm drain system leading to the lake. • Form a volunteer Adopt-a-Stream group to periodically remove trash and litter from the stream

channels feeding Trinity Lake, before they have a chance to enter the lake. • Install a trash receptacle at the pier/boat storage area.





Aquatic Vegetation For many communities, there is often a temptation to desire a “clean” lake, or one free of all aquatic vegetation. Although we understand that individual residents in the Community might request to have the aquatic vegetation in Trinity Lake (e.g. spatterdock, water lilies, and other emergent vegetation) treated and removed from the lake, limited amounts of aquatic vegetation are beneficial for a healthy fish population (and can be aesthetically pleasing).

By law, any chemical treatment must be performed by a licensed pesticide applicator, with a special aquatic designation. Eliminating aquatic vegetation in Trinity Lake will likely result in the growth of more undesirable types of plant material (e.g. algae). Sterile, triploid grass carp (vegetation-eating fish) are best suited for use in small ponds, where aquatic plants are desired for fish and wildlife habitat, and where the grass carp cannot migrate upstream or downstream. Grass carp are effective on most underwater vegetation, NOT on floating or emergent vegetation like we currently observe in Trinity Lake. By law, stocking of grass carp in lakes larger than 10 acres also requires a permit from the NC Wildlife Resources Commission. We would not recommend stocking grass carp in Trinity Lake, nor would a permit likely be granted for this stocking.

A long-term solution to any perceived problem with aquatic vegetation in Trinity Lake should involve treating the cause of the problem, not just the symptom(s). For example, if reducing the amount of aquatic vegetation is truly desired by the Community, deepening the water in the cove areas by mechanically removing the accumulated sediment would eliminate the shallow water than many of these plants need to grow and survive.


• We do not recommend any form of chemical treatment, mechanical removal, or stocking of grass carp at this time in order to reduce or eliminate the aquatic vegetation growing in the lake.

• Continue to identify the types of aquatic vegetation growing in Trinity Lake, and monitor the size of the areas where they are observed to grow.





Sediment Accumulation Years of sediment input to the lake from active stream channels and approximately 1,000 acres of drainage area have created several islands, plumes/deltas, shallow water, and wetland areas in the upstream portion and coves of Trinity Lake. This act of “filling in” is the natural cycle of any pond, lake, or impounded body of water. Based on 2008 aerial photography, evident sediment accumulation may account for approximately 1.5 acres in the upper end of the lake alone. Even when the lake is at full pool (water level at its highest elevation), this area of the lake has no more than a few inches of water depth. To preserve the depth and health of the remaining lake, and to improve the condition of the upper portion of the lake, this accumulated sediment would need to be removed and a rip-rap baffle and forebay system created. The forebay area should be permanently accessible to heavy maintenance equipment, and will act as an easily-maintained area for future sediment removal (e.g. dredging). Note that any work of this type will require notification to, and permits from, the US Army Corps of Engineers and the NC Department of Environment and Natural Resources.

Recommendations (immediate):

• Investigate the existing volume of the lake and exact areas (and depths) of sediment accumulation.

Recommendations (short-term):

• Solicit ballpark cost estimates for future sediment removal and baffle/forebay installation. • Establish a long-term budget for future sediment removal and baffle/forebay installation based on

those ballpark cost estimates. A project of this size could easily cost over $200,000, depending on a variety of factors.

Recommendations (long-term):

• Remove accumulated sediment and install a baffle/forebay system.





Lake Buffer A strip of vegetation, or buffer, should be protected and maintained around the lake. A lake buffer, established as a 30-foot wide “stream buffer” on the Community’s original site plan documents, acts to filter out and limit the amount of sediment and pollutants entering the lake from waterfront properties.

A buffer of trees, shrubs, and ground cover will also act to provide valuable bird and wildlife habitat, prevent bank erosion, and shield the view of residents’ back yards and homes from others enjoying the lake. Please follow any applicable Homeowners’ Association rules and covenants when maintaining the lake buffer. By law, any chemical treatment of vegetation located near the water must be performed by a licensed pesticide applicator, with a special aquatic designation.


• Continue to protect, maintain, and enforce the established lake buffer around the lake. • Work with waterfront property owners to re-establish the lake buffer of trees, shrubs, and ground

cover where needed. • Work with the Homeowners’ Association to re-establish a buffer of trees, shrubs, and ground

cover in waterfront common areas.





Fisheries Management

Recreational fishing appears to be a fairly popular activity on Trinity Lake. If the Community’s goal is to improve the quality of the fish population and fishing opportunities on the lake, certain management activities can be taken to address this desire – conducting research to describe the health of the current fish population, stocking fish to “balance” the population, imposing various size and creel limits on anglers to benefit the fish population, adding underwater structures and areas to attract fish, etc. Recommendations (immediate or short-term):

• Consider conducting a research study of the current fish population in Trinity Lake. The results of this study would direct any future fisheries management efforts.

• Consider conducting a brief survey of the Community’s residents to determine their interest in fishing on the lake, improving the quality of the fish population, expanding opportunities for fishing on the lake, etc.





Additional Resources and Contacts 1. North Carolina Department of Environment and Nat ural Resources

Division of Land Resources – Dam Safety www.dlr.enr.state.nc.us/pages/damsafetyprogram.html

Winston-Salem Regional Office Raleigh Central Office Mr. Shannon Leonard, Assist. Regional Engr. Mr. Steve McEvoy, State Dam Safety Engr. 585 Waughtown St. 1612 Mail Service Center Winston-Salem, NC 27107 Raleigh, NC 27699-1612 336.771.5037 919.733.4574

2. North Carolina Dam Safety Law (1967)

www.dlr.enr.state.nc.us/pages/damsafetylaw1967.html

3. North Carolina Dam Safety Manual (revised 2006) www.dlr.enr.state.nc.us/pages/publications.html#dslinks

4. NC State University – Pond Management Guide

www.ces.ncsu.edu/nreos/wild/fisheries/mgt_guide

5. North Carolina Wildlife Resources Commission www.ncwildlife.org/Fishing/index.htm

6. Guilford County - Watershed Protection and Storm water Management

www.co.guilford.nc.us/watershed_cms/index.html 7. City of Greensboro - Stormwater Management Divis ion

www.greensboro-nc.gov/departments/Water/stormwater

trinity lake - draft management plan · trash, litter, and debris 8 aquatic vegetation 9 sediment...

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