Installing a Sediment Forebay at the TAPP Rain Garden
Da Problem: The upper portion of the large TAPP Rain Garden covers an old pedestrian path. The path had been maintained for years with a base of compacted aggregate to provide a nice solid walking surface. Unfortunately this surface was left in place when the Rain Garden was installed.
|
Da Problem (cont): Rain Garden plants were originally placed in small holes just large enough to fit the previously potted root ball. Surrounding soils were not reworked and amended to provide suitable growing media. As a result plant growth was stunted and the roots grew in circles in their small holes.
|
Da Tools: Two puny fellas worked for about 2-3 hours with the tools shown. There is FREE mulch in the buckets from the County Solid Waste Facility. Not pictured is the erosion fabric cloth and the "Pick-Axe" that was used to break up the cement like surface of the former path.
|
Some of the compacted hardpan surface was left at the base of the sign as a permanent monument and reminder to check your soils.
|
Soil Horizons: The first step was to dig a test hole and check the soil horizons. Fortunately once we dug below the cement like surface and a layer of compacted clay, we found a nice thick layer of loamy sand. In layman's terms this means that any pools should drain relatively quickly, so the depth of the forebay could be fairly deep. In clayey soils or areas with high water tables, the ponding depth can be greatly limited. - As an aside always check for utilities, septic systems, large tree root zones before you start digging.
|
Forebay Shape & Berm: A Pick axe was used to break up the hard surface. We used shovels to form the forebay. Essentially the upper clayey soils were dug out and used to create the berm. When making a berm make sure you compact the dirt (basically place a couple of inches of dirt then compact). The bottom of the forebay was dug well into the sandy subsurface soils. The berm was covered with a fabric blanket to help protect it from erosion.
|
Amend Soils: The surface soils were amended (mixed) with an inch or so of FREE mulch from the County Solid waste facility. An additional layer of fine mulch was placed on top of the amended soils.
|
More fabric matting was used along the flume to protect soils in high velocity flow areas to the bottom of the forebay. We will be monitoring the stabilization of the flume.
|
DONE: The entire forebay was covered with a mix of leaves and pine straw to blend in with the remainder of the Rain Garden...btw a forebay in rain garden terms is a settling basin or plunge pool constructed at the incoming discharge point to allow sediment and debris to settle from incoming stormwater in a location that can be easily maintained.