Houston has a lot of examples of using wet stormwater detention ponds for local irrigation. We call these the purple pipe systems because we require the pumped stormwater to be placed in purple pipes. In order to use this source of irrigation, we need to:
1. have a community committed to allow their water level in the wet detention pond to fluctuate. This requires engineers to consider what the ponds look like in various states of empty.
2. have a good source of stormwater storage. You need about 40" of storage in Houston to irrigate on a normal year. In wet years, we would need less, in dry years we would need more.
3. have a community that is willing to pay some utility costs in return for not paying for others. This requires the utility provider (generally a Municipal Utility District (MUD) to consider the benefits associated with selling stormwater for irrigation instead of treated groundwater or surface water. In an area in which groundwater has a big surcharge (up to $3.00 per 1,000 gallons) it is often a no-brainer.
4. unlike treated water, stormwater irrigation systems don't need as much redundancy, because if we don't irrigate for a couple days, while the system is down for unscheduled maintenance, no one really suffers. It is generally an easy decision when the MUD has to upgrade their water system. Double redundancy plus backup power supply verses single system pumping and no backup power supply but some extra "storm water line" generally sells pretty easily when the MUD is required to upgrade.
5. Baseflow in Houston is all mostly shallow groundwater and wastewater now anyway, so except in a couple big watersheds (Lake Houston, Brazos), we have limited need to regenerate baseflow. I understand California's needs too. Perhaps if they stopped routing their surface water supply through the hottest part of the US in open channels, we could achieve higher efficient use of their water from Nevada/Arizona. I know pumping it expensive, but 85-90% of the water from Arizona not making it to the end users should not be an acceptable standard. I understand it is an acceptable legal standard based on western states water law, but should it be?
Dwayne Culp, Ph.D., Ph.D.,P.E.,M.ASCE
Culp Engineering, LLC
Sent: 07-04-2019 12:14
From: Bart Clark
Subject: Stormwater as a resource
If we think about stormwater on a macro scale, it is used as a resource everywhere. But, I think that you are limiting your question to just run-off from urbanized areas. There are many examples of stormwater being used for irrigation and other uses. I am hoping to steer the conversation to a slightly different tack, so, please excuse me if I am not giving you information you are looking for.
I feel that it is crucial that we think of stormwater as a resource in this period of climate change to help protect our streams and rivers. Everyone has heard that rainfall patterns will change to a more intense and less frequent rainfall events. With this change, isn't it likely that our streams and small rivers will see a reduction in the base flow levels? Because of that, it would appear that more of our perennial streams will have drought like flows in the periods between rainfall events between flood level flows. This situation would likely leave these watercourses with lower "normal" water levels making like more difficult for the current residents and users of those watercourses.
My opinion is that storage of water in watersheds to help maintain base flows will be critical to preserving what we see as a healthy environment. Infiltration is a method of storage that is currently favored by most regulation and standards. But, I am not sure that reliance on this measure alone is up to to the task since it will be applied to just developed/urbanized areas.
Storage of water behind dams to support stream flows and provide water for other uses seems as if it will be a necessity. There is a movement to abandon/remove dams to re-establish a normal flow pattern and normal migration of wildlife through watercourses. There are dams do more harm than good and should be candidates for removal; however, I think it is time that we gave some thought to encouraging dam maintenance and construction as a resource to cope with some of the impacts of climate change.
Bart Clark , PE
Sent: 07-03-2019 15:02
From: Natalya Sokolovskaya
Subject: Stormwater as a resource
Has anyone come across any examples of stormwater being used as a resource (e.g. for irrigation, energy generation, or non-potable uses) rather than something to get rid off? Or is it too polluted to be easily used? I know of some small-scale implementations, mostly rain barrels.
Natalya Sokolovskaya P.E.,M.ASCE