Accidental Aesthetics: Photography of Floating Trash | dornob

Accidental Aesthetics: Photography of Floating Trash

via Accidental Aesthetics: Photography of Floating Trash | dornob.

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.

Maintenance Obligations

Many owners or property managers wonder what their maintenance responsibilities are and how they can be enforced by the regulatory authorities.  We happened upon this maintenance agreement on EPA’s website that is a “typical” maintenance agreement.  These agreements usually run with the land and allow the municipality to maintain or repair the facility if he owner refuses – often then having the power to assess the costs as an addition to the owners anual property tax.

Take a look at the sample agreement  here:

D2b-Ablemarle.pdf (application/pdf Object).

Clogged Pipe – Part 1

These inflow pipes always have water backed up into them which, in this case, made them an ideal location for a pretty aggressive tree. A swamp willow’s roots started growing inside the pipe, and even though the tree was cut down, the roots inside the pipe kept growing and trapping sediment – eventually clogging the pipe. The water back up probably helped sediment settle and build up as well.

Submerged inflow pipes

We began by attempting to jet out the pipe. This means loosening the clog with a jet of water while the vac truck sucks out whatever has been dislodged. Usually this is quite effective, but the dense tree roots made this job more complicated. We’re going to return to the job site with a new plan of attack…

Clogged pipe

FRONTLINE: poisoned waters | PBS

A definite eye-opener, worth the time to view.

FRONTLINE: poisoned waters | PBS.

Every year, Puget Sound suffers an oil spill equal to more than half an Exxon Valdez. It just happens drop by drop.

Amazing statement.  Read it here:

via Local News | Stormwater’s damage to Puget Sound huge, report says | Seattle Times Newspaper.

SWM Facility Embankment Repair – Barrel Relining

One of the exciting aspects of working in stormwater is coming up with unique ways to solve repair problems. At this site, the existing outfall pipe was corroding causing water to erode the soil along the outside of the pipe, a condition known as piping. Eventually, it caused a sinkhole that was visible from the surface. This condition can lead to a failure of the embankment with catastrophic results. Check out this video of a failure.

Positioning the new lining

Rather than dealing with the high cost and disturbance of replacing the entire pipe, we lined the corroding corrugated metal pipe (CMP) with a smooth walled HDPE pipe. The pipe we used was Snap-Tite manufactured by ISCO Industries. Made specifically for this purpose, this pipe actually improved the hydraulic performance of the barrel while significantly extending the lifecycle of the structure. The void between the two pipes was pumped with grout. Of course, the sinkhole was also repaired with compacted clay.

With our design/build approach, we reduced the owner’s cost significantly while accelerating the schedule.

StormCon 2008 LID Site Design Presentation

This paper and presentation explores whether Low Impact Development (LID), as originally contemplated (duplicating existing site hydrology), is really a practical solution.  We used this same example in a national workshop series in 2006.