When the ground is exposed by the removal of natural vegetation or other protective ground cover, it is subject to erosion by wind, rain, and flowing water. The sediment loss is usually such that it is absorbed without significant damage. Erosion and sediment loss, however, of land wherein new construction is occurring, i.e., roads, housing developments, and/or commercial development can be significantly greater than the rate from farmland or forests. Sediment resulting from uncontrolled erosion is a form of water pollution that can damage downstream properties and streams. Sediment pollution also tends to fill storm drain pipes, streams, and rivers thus increasing the potential for flooding. Such sediment tends to fill water supply reservoirs and/or detection basins and reduces useful storage capacity of such basins.
With the introduction of the Clean Water Act, the importance of water quality and the impact of construction on natural streams and watercourses was recognized. Since then, federal, state and local regulations and ordinances have been enacted to insure the impact of new home construction on water quality was minimized. As a result, inlet protection, channel liners, vegetation, seeding and sodding, silt fences and sediment/detention ponds all became associated with construction activity. Most new construction projects or developments are now required to incorporate some level of erosion and sediment control during construction. Today, therefore, it is common practice to incorporate a variety of erosion and sediment control devices and techniques in connection with construction projects.
During construction, sediment control is used where water runoff is concentrated in a stormwater basin comprised of an impoundment below the land disturbance with a drain or sewer pipe leading therefrom. At the beginning of a rainfall event, the basin can be empty. The basin fills, either partially or completely, depending on the amount of rainfall and the volume of resulting runoff, as sediment laden runoff enters. Much of the suspended soil particles in the sediment laden runoff settle to the bottom of the basin. When the stormwater basin fills, sediment water flows into the sewer pipe and flows offsite downstream through sewers.
To control the flow of stormwater into the sewer pipe, a temporary water outlet is usually provided for each stormwater basin. A typical water outlet for a stormwater basin includes a generally L-shaped perforated tube structure. One perforated leg section of such tube structure extends from and is temporarily connected to the sewer pipe or drain. Another perforated leg section of such a known tubular outlet acts as a vertical riser or standpipe. The outlet is intended to meter the flow of water from the stormwater basin so as to cause the basin to fill, thus creating a desired pool of water. As the water sits in the basin, some of the soil particles in the water settle to the bottom of the basin.
The perforations in each leg of the outlet extend about a periphery of each tubular leg section. Those perforations in the lower portion of the outlet drain water from a lower portion of the stormwater basin where the sediment has been deposited. As a result, often times a considerable amount of sediment is drained through the outlet and introduced into the inlet end of the sewer drain causing damage downstream from the stormwater basin. Typically, the size of the outlet and the number or size of the openings in the leg sections of the outlet are neither designed nor constructed in accordance with the size of the particular stormwater basin with which the outlet is to be utilized. These known imprecisely sized outlets can create significant problems during the construction phase of the development. First, they are not sized relative to the size of the stormwater basin they are designed to operate in combination with. Second, and over time, they fail to operate in an efficient and effective manner. Moreover, such known outlets fail to control pollution of the water being directed therethrough. Upon completion of construction, and because the sediment water flow in the basin has substantially halted, the outlet is usually removed from the sewer pipe.
Thus, there is a continuing need and desire for a stormwater pollution management apparatus and method for draining water from a stormwater basin while controlling sediment pollution downstream of the inlet to the sewer pipe or drain from such basin.