Erosion and Sediment Control
Mass Grading: Controlling Site Runoff on the Ground Through: Big Berms, Big Holes, and Groundcover
In the best situations, the approved sediment and erosion control plan for mass grading sites include perhaps a few distinct construction activities: 1) demolition, 2) clearing and grubbing, 3) grading 4) Installation of permanent stormwater measures/devices, and 5) vertical construction of buildings. The misconception that an erosion and sediment control plan with these distinct construction activities can be represented with one phase in an erosion control plan submittal is short sighted. The thought that this “one phase fits all conditions” erosion control plan is adequate to address mass grading with overland flow conditions lasting many months and possibly years through phases 2-4 previously mentioned, is certainly more than short sighted.
A good erosion and sediment control plan for a mass grading site will begin with a strong foundation and construction sequence that includes selective clearing/timbering to install vegetated top dewatering basins along the project perimeter, stable temporary runoff conveyances, and a vegetated buffer upstream of perimeter silt fence. The plan would address critical areas on the projects such as temporary stream crossings with smaller storage structures, stable runoff conveyances, vegetation, and stone approaches. Utilize the trees cleared to create single shredded mulch and preserve it onsite to be used as groundcover through the life of construction. The plan should include minimizing the voids and tie-ins along the project perimeter with the mulch preserved during clearing and grubbing. This plan would be supported with necessary calculations and address other items of concern such as stockpiling, materials handling, staging, material laydown, etc. such that the Regulatory agency reviewing the plan has fewer comments and gets a plan that is approvable. Realistically, that approved plan would also address the use of rolled erosion control product on perimeter slopes as this can play a big role in the success of perimeter measures.
What if the “one phase fits all conditions” erosion control plan is approved? These plans can still be implemented in the field and successful, but usually that success is through the determination and implementation of a great contractor. Let’s learn from plan reviewers, inspectors, and contractors what makes or breaks a mass grading site from an erosion control perspective. In NC we are in a wetter climate than some of our counterparts out west. Much of our soil is sandy clay loam, sites have rock that will need to be blasted, and there are buffers and streams that meander throughout many of our mass graded sites. Many of us have learned that if you don’t have adequate erosion and sediment control measures upstream of the project perimeter, then our streams will become our sediment basins.
This fireside chat will provide an opportunity for attendees to interact, and discuss successful erosion control methods for managing runoff and minimizing erosion and sedimentation through the initial stages of construction where the site is relying on overland flow conditions. Discussions will focus on mass grading sites but revolve around types of erosion control measures that are effective, including these measures on the erosion control plan submittals, the conflict of prescribing “means and methods”, the role of regulators in this process, typical failures, maintenance requirements, and knowing when to move on to the next tool in your toolbelt.