Stormwater Sediment Seperators 1

[davepls]

What is the most economical stormwater sediment seperator?
The use would be suburban 10-acre residential subdivision with (2) storm sewers discharging into a lake.

 

[Ron]

The most economical is a "stilling basin" or detention area that causes the velocity of the runoff to drop to near zero. This is done by sizing a small detention area based on, perhaps, the first 1/2-inch of rainfall, then setting a weir on the side opposite the inlet, for discharge to the lake. This will slow the velocity prior to discharge to the lake and allow the sediment to drop out in the pond. If you anticipate a high sediment content, then you will either have to maintain the pond volume or increase the volume to compensate and reduce your maintenance frequency.

 

[Ron]

One other point I forgot to mention...you need to determine the character of the expected sediment. For example, if your runoff is picking up clayey soil and transporting it, you will need a much larger stilling pond as clay is slow to settle (rate of settlement is related to particle size...small particle size=slow settlement). If particles are mostly sand, or even larger silt particles, the rate of settlement will be fairly quick.

 

[sgwpe1]

What state are you in. In NJ we have very stringent design standards for storm water management. Soil erosion and sediment control plan during construction. Many instances post-construction management requires detention of 1-year storm to 50% of predev discharge (generally requiring outlet structures with multiple stages - includeing at least one small typically 3-inch orifice, and higher storms to reduced levels - one instance post-25-yr must be equal or less than pre-10. Like Ron said detention is the route to settling out TSS (total suspended solids).

In the state of Maryland, alot of storm water quality basins are build with wetland shelves and fringes and wetpool areas for settling and encouraging wetland vegetation for filtering effects.

These all take up land area, which of course the client isnt too happy about.

 

[PECPESC]

What they are forgetting to tell you is that you have to provide for the runoff after the first flush (1/2" - 3/4&quot.
The subsequent runoff has to be routed other than thru the pond/basin. This is usually done by a junction box to separate the first flush and the later runoff. Usually done by weirs or some such method to shift flow patterns in the box.