Stormwater Management for Roadways
Filed in Roadways |
Application of the ordinance as currently written to typical roadway projects has proved challenging over the last 18-years. Publicly maintained roadways are generally in land holdings that reflect the absolute minimum land necessary to accomplish the primary mission of transportation. As is often pointed out by those charged with that mission, “the purpose of a transportation project is not stormwater management”. In this day and age, however, no responsible public official suggests that transportation projects can, or should, ignore stormwater impacts. We do though need to evaluate our approach to stormwater management for public roadways and make sure we get maximum benefit from the infrastructure and tax dollars available to build and maintain it.
A workable application of the current Ordinance has relied heavily on interpretation and intent. A sub-group of the Steering Committee met recently to discuss roadways, and more broadly “linear Transportation Projects” in the context of the Ordinance update, and has a few recommendations that will begin our discussion.
- As we have been discussing throughout this Update, keep the focus on Impervious areas, and changes to impervious areas.
- The changes in impervious surfaces from a roadway project should not cause an increase in flood flows from the right-of-way. This is within the control of the roadway agency, and is a different case than the flow from a cross culvert draining areas through the Right-of-way. Often, an undersized cross-culvert turns the roadway into a low-level dam. The dam attenuates peak flows downstream by “backing up” flood water. Just like a dam, at some event the roadway will overtop, which can cause “traffic damages” in the form of delays and slowed emergency response, and sometimes even more hazardous conditions. So what are the options? If the size of the culvert is increased, is it the roadway agencies responsibility to create a flood control reservoir to mimic action of flood attenuation of the undersized culvert? Different jurisdictions have answered that question differently, but the implications of that answer are enormous for roadway agencies who own very limited land. Very often, a “problem culvert” becomes an institution because of the inability to replace the “dam effect” elsewhere than at that culvert. While no specific recommendation is offered, the issue needs to be further discussed.
- Roadways are key factors in the pollutant loading to a stream, and like all impervious surfaces a contributor to the total runoff volume. Would it be a better focus of the funds spent on stormwater management for roadway projects to require that the “Water Quality Control Volume” be addressed (see earlier post for a discussion)? One of our conclusions in the subgroup was that if we could get strict compliance with the “Water Quality Control Volume”, and the changes to impervious area did not increase discharges, we don’t really need roadway stormwater infrastructure to do much else except of course drain the road.
- Simple engineering applications, like the unit area detention nomagraph already used for roadway projects, are usually as technical as we need to get for the limited real impact roadways have.
So, what are your thoughts on roadways?
Tuesday, March 9th 2010 at 9:44 am |
The “DUDOT rules” were as much a response to public perception (Hey, why do we need to do this stormwater stuff, if you aren’t) as they were to the actual increase in imperviousness. As such, I think they are a good compromise. However, I think applying VQCV principles would grant a better benefit to the public.
Thursday, April 8th 2010 at 8:16 am |
I agree roadways should be treated differently and only be required to not cause an increase flood flows from the ROW. However, it’s important to clarify how this will be interpreted and applied. Three issues come to mind. First, there is a difference between an existing roadway and a new roadway that is to be constructed as part of a development where there are opportunities to provide the full detention to meet the 0.1 cfs/acre requirement. This should be addressed.
Secondly, will all storm events need to be evaluated or just the 1% storm event? I think only the later needs to be considered.
And lastly, sometimes it may be difficult or too costly to provide the total WQCV and BMP on-site within the ROW that is needed to treat all the pollutants of concern. This depends on many factors such as which pollutants are we trying to address, the level of treatment, available ROW, etc. I believe it’s important to address water quality, but there should be alternatives in place to help municipalities comply while still treating storm water runoff. This could be accomplished by off-site WQCV and BMPs and fee in lieu of BMPs.
Thursday, April 8th 2010 at 8:26 am |
I believe it’s the community’s responsibility to address increses in flood plain heights due to incresing a problem culvert’s flow capacity. Municipalities should not be allowed to transfer the problem downstream just because it causes a problem upstream or at the culvert. These are difficult situations that I don’t think we can necessarily address them within the Ordinance and are probably better handled as a “flood control project” rather than development. I think this would give municipalities better opportunities to address the “problem culvert” while still addressing the increased flows.
Monday, April 26th 2010 at 10:39 am |
1. It is not clear to me that there is any significant difference in the runoff pollutants from a new pavement, a resurfaced pavement and or an existing pavement.
2. I also feel that cars drop pollutants, utilities disrupt the public right of way and trees drop pollutants. Snow plow operations drop salt. The road receives pollutants but is not the generator of pollutants. So the focus should be on regulating cars, utilities, and salt not roads. The obvious issue is road safety in the winter versus water quality. Trees are planted to add aesthetics for the public. Yet treee are obstructions in the right of way capable of hurting people if a car crashes into one of them. So each contributor of pollutants has balancing arguments. What level of pollutants becomes the tipping point for addressing water quality on roads? And who pays for the water quality improvements?
3. Roads in existance before the creation of the countywide ordinance and any water quality updtaes would seem to be exempt from regulation. We need a lawyer’s interepretation of the intent to regulate a pre exisitng segment of public infrastructure.
4. Total costs of regulating non point source runoff still need to be addressed. Roads would be a good place to really consider the impacts on local governemnt of trying to regulate roadways for water quality.
5. I note that a Senator from Minnesota wants to take “navigable” out of the the Clean Water Act. Extending fEderal jurisdiction to the local level would disrupt local oversight and needs to be watched closely by the County as it relates to roads and everything else.
6. We should discuss the culvert issue.