Construction Journal David Shanahan Seth Lawrence-Slavas


A very rainy start to this week!


In Fig.2.1 the utilities contractor has installed two storm water settling tanks. The one in the forground is black water septic settling tank which is directly connected to town sewer. The one up front is a traditional runoff catchment tank with a baffle to remove any trash and large particulates. The underground drainage connects directly to this tank.

Fig. 2.2 Secondary catchment tank. Protruding are the subterranean drains starting at the footings and finishing nearly 20 ft away here.

Fig 2.3. A 12 inch deep bed of coarse rock no smaller than 4 inches in diameter is placed at the exit of exterior drain. This helps with erosion associated with strong outlet flow.

Fig 2.4 (above) and 2.5 (below). The tops of the pvc perimeter drains can be seen sticking above the paved surface and the dirt. Eventually these will be connected to the gutters connecting the drainage system

Drainage and Storm water management is necessary for proper movement and filtering of runoff water from roofs, parking lots, driveways, and sidewalks. There are many different types and management approaches that a designer can follow. These systems can consist of gutters, downspouts, perforated pipes, foundation drains, catchment tanks, Bioswales, and landscaping to acquire adequate drainage and water shed protection.

Grading and slope of surface (Swales)

Finish grading of the drainage plane is necessary to ensure any surface water is able to move away from the building. Ideal grade is a 2% grade away from the building. This grade specifically allows for water to slowly move away from the structure and percolate down through the soil layer. Diverging from this 2% in either direction can create serious issues. Too much and erosion of top soil becomes likely. Too little and pooling, and back flowing into the foundation becomes the issue.

A preferred sustainable approach to storm water management breaks the project into three design goals.

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