Stormwater management plan example for residential?

senator13July 24, 2010

We are building a home in Maryland and the county just approved new stormwater guidelines. We are going with a rain garden plan, and my husband was able to complete the calculations. However, he is stuck on the storm water calculations, and I am currently working to find out more information (like a residential sample, instead of a commercial site) to determine what is acceptable. The Maryland guidlines are helpful, but there is not quite enough information for me to know which numbers to plug in without concern that the county will quickly discredit the work. Also, I am not sure of the industry practice answer when it comes to interpreting the results. Part of the issue is the manual addresses commercial and residential simultaneously, so the actual residential analysis requirement is a little fuzzy to me. The manual is based on best management practices, and the threshold requirements are not always clearly stated. The goal is to set the pre-development norm at woods with actual soil, and then demonstrate that the post-development maintains the necessary parameters at that woods baseline.

So I am trying to get an example from someone on what their residential stormwater management plan looks like. Bonus points if you live in Maryland:), but I think any plan at this point might give us a better sense on what need to be on the residential vs. commericial plan.

Thanks if you got through all of that!

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Here in Massachusetts residential projects are exempt from having to have a stormwater management plan. Make sure that you need to have one for Maryland.

When they are required here, it has to be done by a licensed civil engineer (stamped and signed).

What body will be required to review and approve it?

    Bookmark   July 24, 2010 at 8:39AM
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I did a quick search on the subject and it appears that the revised MD stormwater law is being questioned and a recent public hearing scheduled for May, 2010 on the matter has been canceled. Apparently you are not the only one designing in the dark. From what I could glean local municipalities have the right to approve stormwater management on residential properties. It is my guess that your local planning board is the authority to sign off on your whole building project including this. Suggest you gather up your plans, take them to your local building department and say "help". Ask there for guidance. Ask if the stormwater plan needs an official stamp from a licensed civil engineer or landscape architect. Hopefully you will receive some assistance. With this new law if I were building in MD I would use a large architectural firm which has an in-house civil engineer. That way the package would be complete, ready for submittal and approval.

    Bookmark   July 24, 2010 at 1:38PM
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For Maryland, you can use a professional engineer, lanscape engineer, or anyone "deemed acceptable." My husband is a PE and has done engineering for 20 years, so he probably has more experience with these types of formulas than most. Having said that, the state provides "guidance" based on best practices, but they don't give a clear example of what might be needed in the calculations for most residential builds. Does that make sense? The county is also at a loss of how to do this. They did update the ordinance recently which helps slightly, but they have no examples. In the past, drywells were okay, but now they are not. Yes, it is like playing a game without having the directions...sigh.

    Bookmark   July 24, 2010 at 1:53PM
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If your husband is knowledgable and has credentials, the board reviewing it more likely will accept his knowledge and the basic plan that he has already figured out because they'll understanf that he knows way more about it than they do.

If they do have an expert on the board or on staff, (s)he'll them him what concerns they have and he'll be able to fix it.

Why does he have his wife asking for answers on a garden design forum?

    Bookmark   July 24, 2010 at 8:57PM
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Having taken the Rutgers Rain Garden Specialist/Trainer training, I have the formulas for New Jersey, but don't know if they would be applicable to the rainfall and regulatory requirements of Maryland. However, in researching this topic, I have seen see a lot of information shared from one state to another.

If you'd like, take a look at the materials listed in the link below and see if they might be helpful to you. "Rain Garden Design" and "Rain Garden Site Visit Worksheet (Pre-Installation) may be the most helpful for you. Please note, though, that the formulas are for New JerseyÂs Water Quality Design Storm of 1.25" of rain over a period of two hours.

Good luck to you both!

    Bookmark   July 25, 2010 at 1:21AM
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I feel your pain. Go to or call your City's permit office and ask to speak to whoever is handling the sign off of this plan. That person may be overwhelmed or not sure of what he actually wants from you. Ask to see a sample or a copy of one that was deemed acceptable and go from there. They may not require a PE stamp for this yet but it is coming. The calcs may not be required if you specify the BMPs you will use to control run off or retain run off and filter through bio-screening materials. Residential requirements should be considerable less stringent than commercial. Unfortunately these requirements have gone way beyond reasonable precautions for sediment retention and water quality runoff at a reasonable cost. Logic is no longer a factor here. It has spawned a new industry. Good luck. Aloha

    Bookmark   July 25, 2010 at 12:19PM
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Of course, you still have to meet whatever your local requirements are, but if there's any flexibility, here are two additional tidbits from our training:

1. A rain garden can be up to 30% smaller than optimal size and still control almost 90% of the annual runoff.

2. The first 20 minutes of a storm is when most pollution is carried of into streams.

    Bookmark   July 25, 2010 at 12:34PM
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Thank you everyone for your feedback. He is 95% complete with the help of my father who was a soil conservationist for 30 years. He still needs to write the narrative (straight forward), complete the rain garden calculations (straight forward), and complete the ESD storage volume and reduced RCNs (this he needs to research more).

This has been frustrating because there is little to no information out there that gives specific examples for residential. Most manuals mix information for residential and commericial, and even PE's are not real familiar with the guidelines for residential around here. The county, who has great people, really has no idea of how to handle this either. And for added pleasure, we need to get our plan approved before the rest of the building package can be submitted. Which is why we are hoping for a small amount of feedback after it is submitted.

Sorry if I didn't ask the right board about this. I posted it a week or so ago on the Home Building forum, and got nothing. I thought that with some of your expertise and interest in landscaping, you might have some suggestions for resources.

Thanks again, and cross those fingers!

    Bookmark   July 26, 2010 at 7:14AM
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It looks like the link I mentioned did not post. Here it is in case you can still use the information.

Here is a link that might be useful: Water Resources Program

    Bookmark   July 26, 2010 at 8:10AM
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And, as there is no Rain Garden Forum, I cannot think of a better forum in which to have posed your question!

In time I expect we will be seeing more interest in this aspect of landscaping - sometimes mandated, but often voluntary.

Good luck with your application and your project!

    Bookmark   July 26, 2010 at 8:14AM
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Thank you so much agardenstateof_mind for your helpful resources and kind words!

    Bookmark   July 26, 2010 at 9:33PM
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Senator, we hope you will continue to keep us posted on your progress. It must be frustrating to have the requirement but not the information. Planning Departments hopefully are working on this.

Perhaps a lot of us can incorporate rain garden and stormwater plans. While not mandated most places, it is good stewardship.

My best, Rosie, Sugar Hill, GA

    Bookmark   July 27, 2010 at 7:58PM
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Will do, Rosie. Thanks for the kind, uplifting words!

    Bookmark   July 28, 2010 at 9:30PM
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Please keep us posted. It sounds like your husband has some good resourses to work from. We have a grant program that picks homes and areas that if meet the criteria will have some help with the cost of installing the rain garden. With a reduction of utility cost. As I understand it we would use the runoff from our down spouts that feed the garden. We use native plant that can take drought. We have many plant materials that will fit the bill but should look good in a design. I have seen some of these and they look great. Very well put together. I remain cautious of what I see as a possible trend that businesses may take advantage of a concept, that for me atleast I have not seen as proven in a large scale residential or commercial area. If anyone out there can suggest a site that may have and ongoing project let me know. I'm considering this for my own home.

    Bookmark   July 29, 2010 at 3:27AM
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Rain gardens have been discussed numerous times on this Forum. CT passed a law mandating them about five years ago. Those wishing to do more research on the subject should find helpful information/designs by searching: rain gardens + CT.

    Bookmark   July 29, 2010 at 7:20AM
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We just had our detention basin dug in this past week. This is an example of what you don't want. We tried to have it redesigned, but really did not have any luck with the township. Residential sites with less than 10k square feet of impervious soil are supposed to be exempt, but a "concerned" resident complained about runoff during a township meeting. That required the full ordinance be adhered to, utilizing a PE to perform the design. We were told the pond won't really be noticable after it is installed. The pond is 120 feet long.

Here is a link that might be useful:

    Bookmark   August 30, 2010 at 11:20PM
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Can I ask what county this is for? My husband is a builder in Anne Arundel and I've honestly never heard of any homeowner having to do that before. The builder or contractor has always taken care of that. Is it b/c you are your own contractor? Is the house all by itself or in a community?

I would contact the local permit office and ask them. Maybe they can point you in the right direction. I would hate to see you spend more time and money on something that doesn't need to be done. A rain garden might work just as good but it all depends on your site.

    Bookmark   August 31, 2010 at 7:13AM
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