Stormwater 101: Detention and Retention Basins

A common conventional method for managing stormwater is a stormwater basin.  Basins are meant to collect stormwater and slowly release it at a controlled rate so that downstream areas are not flooded or eroded.   While effective for flood control, these practices have significant limitations for water quality treatment and for preventing impacts to stream systems.

Detention (dry) basin

The main difference between a detention and a retention basin is whether or not it has a permanent pool of water – like a traditional “pond”.   The water level is established by the low flow orifice.  Most of the time the orifice is part of a metal or concrete structure called a riser.  A detention, or dry, basin has an orifice level with the bottom of the basin so that all of the water eventually drains out and it remains dry between storms – hence, a dry basin.  Retention basins have a riser with an orifice at a higher point so that it retains a permanent pool of water.

Retention (wet) basin

The basins themselves are important for storing and slowing (attenuating) the runoff from impervious surfaces such as rooftops or pavement.  The amount of treatment, or cleaning, of the water is limited.  Dry detention basins control flood flows only.  A retention basin can also provide water quality benefits by reducing sediments and attached pollutants.

Water in the Southwest

After visiting the Scottsdale area recently, we were struck by the incredible development and population in an area that has very little water.  Irrigated golf courses everywhere?  Really?  While we’re sure it has been considered a marvel of engineering and mankind’s triumph over nature to be able to support such infrastructure in the middle of the desert, in the terms of this millennium’s trends  (ie sustainablilty), it seems quite bizarre.  That we are from the wet east coast no doubt plays into this observation.

Nonetheless, the following article points out the challenges of over-development in arid areas and the folly in some water politics.  That rainwater harvesting and greywater reuse is illegal in some areas illustrates the crazy misguided politics.  Seems to be pretty much the opposite of sustainability at the most basic level.

Lake Mead Is Drying Up | GOOD.

Arid dwellers, do comment to share your perspective.

Clogged Pipe – Part 2

We returned to the site to finish unclogging this pipe.  See Part 1 here. This time we brought a tool to pull out the roots.  The equipment we had with us also prepared us to remove the pipe if needed.

It wasn’t as satisfying as it would have been if the whole thing came out with one big yank.  The hook only grabbed bits at a time so we had to use the hook with a long rod to pull out some.  We then used the vac truck to jet out some more and kept alternating back and forth.  Using this method, we cleaned out approximately 42 feet of pipe.

The hook used to grab pieces of the clog. Next to his feet is a lump of mud, roots and trash that was pulled out. The excavator did the pulling.

More roots and mud removed from the pipe. The vac truck (the pipe to the left) is removing the water with the highest concentration of sediment.