Erosion Control Measures: Their Strengths and Weaknesses

One important service we offer to clients is erosion and sediment control. Erosion, the process where soil is gradually worn away by water, wind, or gravity, wears away at the foundations of structures and contributes to desertification. It also lowers the quality of water in lakes, rivers, and steams. As erosion damage can be costly and dangerous to humans and the environment, civil-site design often includes providing proper erosion and sediment control measures. Here are three methods that, when effectively used, significantly reduce erosion damage to streams, buildings, and properties.

Riprap at Lake Orange

Riprap

Riprap is a layer of different sized stones that reduce erosion on steep surfaces. These disrupt the flow of water that would normally run down a slope which helps to keep the soil in place and protect stream banks, dams, and bridge crossings. Riprap is low maintenance and durable and can be used to protect infrastructure; however, it has environmental drawbacks that cause the NCDEQ to regulate it. Riprap can heat up ponds and streams and the fact that it is made of rock can affect animal habitats. To avoid environmental damage, riprap is best combined with other methods such as vegetation to protect the soil, provide habitats, and maintain water temperature.

Vegetation

Vegetation at South Mountain Dam

Using native plants to stabilize the soil is both an act of good stewardship as well as being one of the most effective ways of avoiding erosion. Vegetation helps to shield soil from rain and potential scour from overland flow. Plants also naturally remove water from the soil and will spread naturally, thus maintaining and increasing the area being protected. Once established, vegetation is cost-effective and self-sustaining, but that establishment can take time. Vegetation can even be considered high maintenance when native plants are mismanaged, and it cannot grow in steep or naturally rocky areas without support. While vegetation is one of the most effect and sustainable options, it can need to be combined with riprap or retaining walls and requires proper management.

Retaining Walls

A retaining wall in Charlotte

Retaining walls are generally used in areas with sharp elevation changes. They hold back and stabilize topsoil by stopping the flow of water outright. This halts the process of erosion and allows the water to slowly filter into the ground. Retaining walls are durable and usually require little maintenance once built. However, they are expensive to design and build. Retaining walls can also be environmentally harmful since they’re subject to the erosion they try to prevent and can disrupt the natural environment. Over time, the foundations can become eroded by water filtering down through the soil, causing potential collapses. Sustainable drainage measures are used to reduce this damage, and minimal excavation, with the use of local materials, can help mitigate the environmental harm.

All three methods have their advantages and weaknesses, and through careful planning and sustainable practices, all of them are useful in preventing erosion damage. North Carolina’s risk of erosion, particularly along the coast and even in the triangle area, is quite high, so A&O strives to find the best long-term, low maintenance solutions that allow us to follow the command to be good stewards that we have been given. If you are interested in learning more about Alpha & Omega Group’s work in erosion control, please visit our page for the Nantahala Shooting Ranges.

Stormwater Control Measures: A Brief Introduction

One hazard of urbanization is stormwater runoff. Water running off from lawns, houses, and commercial buildings causes erosion damage and can be toxic for plants and wildlife when it reaches streams or ponds. It can also be toxic for humans when it enters our drinking water. To avoid the worst effects, stormwater control measures (SCMs) exist to trap runoff, release it slowly, and remove pollutants. However, not all SCMs perform the same way. Different SCMs are chosen based local regulations, topography, and the land available. Here are a few SCMs that we at A&O design and use in many of our development projects.

Dry Detention Ponds

Stormwater Management in action

Dry detention ponds work very well to remove pollutants and control water flow. In a dry detention pond, stormwater flows into a basin that fills and then slowly releases that water over a few days to allow solids and pollutants to settle rather than entering nearby streams. While this process only filters minimal pollutants, it works to avoid sudden flooding and erosion damage. The trapped water releases slowly, and that works to maintain a steady water level.

Bioretention Ponds

Bioretention ponds are a way to improve stormwater quality, aid in erosion control, and provide landscaping. Bioretention ponds capture the “first flush” of stormwater, which usually contains the highest concentration of pollutants. The trapped water flows through specially engineered soils to filter out toxins and microbes. It filters through a layer of mulch and specially chosen plants or grass and then the rest of the engineered soil. Roots, bacteria, and insects then remove excess nitrogen and phosphorus, much like a natural ecosystem. Usually, an underdrain piping system built under the pond collects the infiltrated water where it flows into nearby waterways.

A Bio Retention Pond

Permeable Pavement

Permeable pavement is designed to mitigate flooding and provide detention for the runoff of impervious pavement and concrete. The pavement can be made of porous concrete, porous asphalt, pavers, and rigid plastic grid panels filled with stone to allow water passage. This system allows stormwater to gradually filter through underlying soil or be collected in an underdrain and released through a slow discharge and filtering. Due to sand and silt clogging pores, permeable pavement tends to require regular maintenance.

Level Spreaders

Level spreaders are another method to reduce erosion impacts. This is usually the last element of a series of SCMs to discharge stormwater without erosion damage. Level spreaders are a level, shallow ditch with a lip made from some non-erodible material on its down-stream side. During rain, stormwater fills the ditch, but this lip acts like a buffer so that the water must build up and spill evenly into a gravel verge. It then flows through a vegetative filter into an undisturbed wooded area. This method controls flooding and erosion and helps to purify the water. When it eventually flows into nearby waterways, it does so at a controlled speed and with far less pollutants.

A Level Spreader

Stormwater control is a required part of any site design from urban roadways to mountain shooting ranges. Every method has strengths and weaknesses that may make it better suited for a particular task or environment. We know that the stormwater infrastructure and SCM designs we provide offer critical stormwater mitigation that reduces the flooding and pollution on every site we work on. Alpha & Omega Group is proud that our work provides safety and helps us act as good stewards of the precious resource of water.

If you want to learn more about some of our stormwater work, please visit our project pages, including the Raleigh Chinese Christian Church, our award-winning Mountains to the Sea design for Lincoln Heights, and our ongoing work for the Nantahala Shooting Ranges.