Mitigating 15% of stormwater for this credit may be more doable than you think. If a site was not designed with stormwater mitigation in mind, or does not have the benefit of extensive vegetated areas relative to the amount of impervious site area, you may need to make a significant investment in strategies like cisterns, green roofs, water retention features, and detention ponds. However, a typical project site may have a favorable ratio of vegetated area to impervious hardscapeThe inanimate elements of the building landscaping. It includes pavement, roadways, stonewalls, wood and synthetic decking, concrete paths and sidewalks, and concrete, brick, and tile patios. that would naturally mitigate enough stormwater runoff, eliminating the need for major modifications in order to achieve this credit. While it is important to have a professional calculate the required amount of vegetated area needed, a hardscape-to-vegetated area ratio of as much as five-to-one may be suitable.
Owners and facility managers can assess current conditions and, if necessary, work closely with a stormwater engineer or other professional to determine an effective stormwater management plan that is appropriate to the site’s climate, topography and local stormwater ordinances.
The approach for achieving this credit varies dramatically across different regions and climate zones. The strategies employed in an urban environment, where water is discharged to a municipally controlled and maintained master system, will vary significantly from the approach for a rural project that discharges to smaller streams or lakes with higher water quality standards. Regions that are generally dry and need to retain and reuse rainwater, but also have seasonally heavy rainfall, can benefit greatly from collection and storage strategies.
Stormwater captured in cisterns may be treated and used for irrigation and and indoor uses such as toilet flushing, fire suppression, laundry, and cooling tower make-up water.
NOAA provides a great resource for finding information on the 2-year 24-hour storm. For some locations in the U.S., the site allows you to navigate to a specific locale and generates a table of rainfall intensities, including for the 2-year 24-hour design storm. For the other states, it lets you download isopluvial maps.
This is mostly a judgment call and if you’re concerned about questions during the review process, a great way to make your case is with photos or with a narrative describing your methodology to determine the slope.
If the manufacturer publishes or can provide the runoff coefficient for your system, use that. For other surfaces where the data is not available, chose the closest surface type from the credit form and go with that.
The best place to find this type of data is typically through public agency or semi-public agencies like universities or other organizations. But if you can’t find data specific to the 2-year 24-hour storm, there is an alternative compliance path published by USGBC in the ACP Documentation Guidance for Projects Outside the U.S.
If the water body can contain the rainfall event with no discharge to the sanitary sewer, then the runoff coefficient is essentially zero. If, on the other hand, the rain that falls directly into the water body raises the water level sufficiently to overflow into the sanitary sewer, the runoff coefficient is 1.0. For example, pools will often have a bit of freeboard before the water level rises enough to overflow and this will allow you to capture the rainfall, and even make up for some evaporation that would otherwise be made up using potable waterWater that meets or exceeds U.S. Environmental Protection Agency drinking water quality standards (or a local equivalent outside the U.S.) and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems..
Porous pavers used for site hardscape areas can reduce runoff.Perform a site inventory cataloging surface types, such as asphalt, concrete, roof areas, and landscaped areas. Use the LEED template to assess the percent of stormwater managed based on site perviousness.
The LEED Online credit form contains a built-in calculator that uses runoff coefficients of different surface types to determine infiltration volumes.
If the project site contains a number of different surface slopes and grades, you can simplify the calculation process by classifying the majority of appropriate surface areas as “steep.” This will generate the most conservative calculation of stormwater mitigation.
If cisterns, detention ponds, or other stormwater collection systems exist on site, assess their capacity and the area of surfaces from which they collect water, based on design documents or other system information.
Research region-specific data for the total annual rainfall and the 2-year, 24-hour frequency storm. See the Documentation Toolkit for an example of this kind of assessment, and see the step-by-step LEEDuser strategy page on getting the stormwater data you need.
You may use online tools to determine region-specific rainfall amounts. However, since this data is not always readily available online, the best way to track down this information may be to contact your city or county stormwater management officials directly.
Investigate opportunities for increased stormwater mitigation (based on the inventory results) through water harvesting techniques or modifying surface areas to increase the amount of pervious surface.
Substitute porous paving materials in place of conventional asphalt and concrete. This may require installing a new sub-base and is not as simple as repaving.
Harvest stormwater in tanks and cisterns for reuse. Stormwater may be treated and used for irrigation and indoor uses such as toilet flushing, fire suppression, laundry, and cooling tower make-up water.
Install green roofs to reduce the runoff coefficient of the roof area.
For urban buildings with small sites, green roofs and rainwater collection and reuse systems are the most likely strategies to bring the project to compliance with this credit. While it is important to have a professional calculate the required amount of vegetated area needed to mitigate 15% of onsite rainfall, a reasonable rule of thumb is that you’ll need to cover at least 20% of the site area with a green roof or other vegetation.
Convert site area to include infiltration swales, rain gardens, vegetated filter strips and retention ponds.
Consult with local authorities and ordinances to learn about regulations on stormwater detention features that may influence your management plan.
Stormwater capture may be illegal in certain areas of the country, such as Colorado, where existing downstream water rights take precedence.
Develop a preventative maintenance plan to evaluate stormwater management facilities regularly and ensure optimal performance.
Stormwater reuse costs are minimal for irrigation, moderate for make-up water, and significantly higher for use in indoor plumbing fixtures.
Monitor all stormwater mitigation features, including natural areas as well as mechanical harvesting equipment, to gauge retention efficiency and ensure proper function.
Perform all routine required maintenance and repairs within 60 days of inspection and keep an inspection report and maintenance log.
Maintenance costs will vary depending on the equipment and techniques in use, but regular preventative maintenance will help to minimize those costs.
Excerpted from LEED 2009 for Existing Buildings: Operations & Maintenance
To limit disruption of natural hydrology by reducing impervious cover, increasing on-site infiltration, reducing or eliminating pollution from stormwater runoff and eliminating contaminants.
During the performance period, implement a stormwater management plan that infiltrates, collects and reuses runoff or evapotranspirates runoff from at least 15% of the precipitation falling on the whole project site both for an average weather year and for the 2-year, 24-hour design stormA 2-year, 24-hour design storm is a nationally accepted rate that represents the largest amount of rainfall expected over a 24-hour period during a 2-year interval. The rate is the basis for planning and designing stormwater management facilities and features..
Implement an annual inspection program of all stormwater management facilities to confirm continued performance. Maintain documentation of inspection, including identification of areas of erosion, maintenance needs and repairs. Perform all routine required maintenance, necessary repairs or stabilization within 60 days of inspection.
Use Low Impact Development (LIDLow-impact development: an approach to managing rainwater runoff that emphasizes on-site natural features to protect water quality, by replicating the natural land cover hydrologic regime of watersheds, and addressing runoff close to its source. Examples include better site design principles (e.g., minimizing land disturbance, preserving vegetation, minimizing impervious cover), and design practices (e.g., rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, soil amendments). These are engineered practices that may require specialized design assistance.)1 practices to capture and treat water from 25% of the impervious surfacesAn area of ground that development and building have modified in such a way that precipitation cannot infiltrate downward through the soil. Examples of impervious surfaces include roofs, paved roads and parking areas, sidewalks, and soils that have been compacted either by design or by use. for the 95th percentile of regional or local rainfall events.
Collect and reuse stormwater for nonpotable uses such as landscape irrigation, toilet and urinal flushing, and custodial uses. During facility or site alterations or additions, specify the use of alternative surfaces (e.g., vegetated roofs, pervious pavement or grid pavers) and nonstructural techniques (e.g., rain gardens, vegetated swales, disconnection of imperviousnessResistance to penetration by a liquid and is calculated as the percentage of area covered by a paving system that does not allow moisture to soak into the ground., rainwater recycling) to improve perviousness, thereby restoring or maintaining natural stormwater flows. Incorporate stormwater management facilities into routine preventive and corrective maintenance programs.
1.The baseline condition is the site condition prior to LEED registration.
2. Low impact development (LIDLow-impact development: an approach to managing rainwater runoff that emphasizes on-site natural features to protect water quality, by replicating the natural land cover hydrologic regime of watersheds, and addressing runoff close to its source. Examples include better site design principles (e.g., minimizing land disturbance, preserving vegetation, minimizing impervious cover), and design practices (e.g., rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, soil amendments). These are engineered practices that may require specialized design assistance.) is an approach to managing stormwater runoff that emphasizes on-site natural features to protect water quality byreplicating the natural land cover hydrologic regime of watersheds and addressing runoff close to its source. Examples include better site design principles such as minimizing land disturbance, preserving vegetation, minimizing impervious cover, and design practices like rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, and soil amendments. These are engineered practices that may require specialized design assistance.
This website provides historic rainfall data and isopluvial maps for various storm events.
A nonprofit dedicated to disseminating watershed-protection information to community leaders and watershed managers, the Center offers online resources, training seminars and a journal, The Practice of Watershed Protection.
EPA provides valuable information on low-impact developmentAn approach to managing rainwater runoff that emphasizes on-site natural features to protect water quality, by replicating the natural land cover hydrologic regime of watersheds, and addressing runoff close to its source. Examples include better site design principles (e.g., minimizing land disturbance, preserving vegetation, minimizing impervious cover), and design practices (e.g., rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, soil amendments). These are engineered practices that may require specialized design assistance. through fact sheets, design guides and cost estimates for low-impact development strategies that reduce stormwater runoff.
EPA offers help on managing stormwater, including fact sheets on the six minimum control measures for best management practices.
This site for practitioners and local government officials provides technical assistance on stormwater management issues.
NRCS provides technical resources and financial assistance to land-users, communities, and local governments for conserving soil, water and natural resources.
This article discusses how to work around Colorado's water use laws when managing stormwater.
You'll need to document stormwater inspections to confirm continued performance.
Perform stormwater management calculations to assess the percentage of precipitation mitigated by the project site.
This sample LEED Online form with tips demonstrates how to document SSc6.
Sample LEED Online forms for all rating systems and versions are available on the USGBC website.
I am having the same problem with the online form and pdf for ssc6. Has anyone figured this out?
Past conversations have said that the volume stored in the soil mix and the dead storage above the soil mix (below the overflow) in bio-retention basins can be used to offset the runoff volume increase from pre to post development conditions. We have clay soils with low permeability, so we install underdrains in our bio-retention cells, a few inches above the bottom of the stone. There is a 24 hour design draw down time. Can the dead storage above the soil mix be used to reduce the post development volume? Can the soil mix, with a 0.17 porosity, be used as offsetting volume if there is an underdrain?
If I were doing this, I would route the under drain, and the infiltration. You aren't going to get credit for whatever bleeds out of the underdrain, but even the worst of soils infiltrate something.
Simply providing the volume required to manage the delta does not meet this credit, it needs to infiltrate in this situation.
Does anyone have an accurate way of converting total inches of rainfall to cubic feet as required by the credit?
Please have a civil engineer do your stormwater calculations.
Are there any requirements on who must perform the Stormwater system inspection for LEED
There aren't any specific requirements, but it's common for a member of the engineering team to complete the stormwater inspection.
OK it seems like, from reading the questions and responses here, that there is absolutely no clear guidance on how to come up with the "rainfall interval event" in order to perform the drawdown calculation. Am I missing something, or is there clear language from LEED somewhere that will clear this up for people?
Keep in mind the LEED rating system is not a stormwater management ordinance. There is no (to my knowledge) specified dewatering time. 72 hours is kind of standard industry practice, but is no way a hard and fast rule. This actually stems from detention basins, and helping to stave off mosquitoes. The dewatering equation that appears in the reference guides looks like it was taken from the MD BMPBest Management Practice manual, which required a certain time for some BMP while LEED doesn't.
I would suggest having your civil engineer make a determination as to what you believe your best option is for your project.
In the absence of dewatering in 72 hours, I would calculate your actual drawdown for those 3 days, then provide the delta volume for a second 2-year storm event (still only like a 0.5% probability of happening back to back within 72 hours).
Thanks for the quick reply Michael. I'm actually hoping to reuse the stormwater for toilet flushing, and at a required 3,000 gallon storage capacity (for the 2-year, 24-hour event) 72 hours is not going to happen for us as we don't use anywhere near 1,000 gallons per day. I'll use your suggestion for the delta volume calculation and see how it goes.
Hello there. My team and I are certifying a building in Brazilia, Brazil. I would like to check if I'm right about the procedure to accomplish SSc6.
1) Find the average weather year precipitation;
2) Separete all areas of the total site (example: asphalt, concrete, brick, ...)
3) Calculate the total runoff volume (Q = C i A): sum all Q's from all different types of areas
4) Calculate the volume of captured runoff by a cistern
5) Evaluate the minimum drawdown rate
6) Evaluate if the volume of captured runoff is bigger than 15% of the total runoff volume.
Is that all right?
Just to check, if the ratio between impervious area and green area is equal to 5, I don't need to worry about cisterns, right?
By the way, how am I supposed to extimate the rainfall event interval?
And the last question is: average rainfall event = total precipitation / number of rainfalls ?
Thank you so much!! God bless you all.
Hi Hugo, the Rational MethodA formula that can be used for calculating stormwater flow rates. Q = CIA, where C represents a coefficient for physical drainage area, I is the rainfall intensity, and A is area. The method is suitable for watersheds smaller than 300 acres in size. (Q=CIA) will give you a runoff rate, not volume. You need to use another methodology to determine runoff volume (I prefer SCS).
Average rainfall is the average depth, you may be able to find this somewhere in local weather data.
I recommend that you use a civil engineer or other stormwater professional to develop your stormwater management program.
Both uploads SSc6-3 and SSc6-4 require the provision of “a copy of the most recent stormwater inspection and a log showing that any needed maintenance or repairs were performed within 60 days of the inspection that uncovered them”. Are two different inspections necessary one during the performance and another one during the establishment period?
The credit requires that an annual inspection program of all stormwater management facilities be implemented to confirm continued performance, that documentation exist for the inspection and that all routine required maintenance and necessary repairs or stabilization occur within 60 days of inspection. The key here being that it’s an annual inspection program.
For the documentation of this credit, it should be sufficient to perform an inspection during the performance period and upload the inspection report and a log showing that any needed maintenance or repairs were performed within 60 days to both sections. If the project is a recertification, annual inspection logs would be submitted.
Thank you Karin. That said do you think that we still need to provide two different inspection reports, one for Upload SSc6-3 (Establishment) and an additional one for Upload SSc6-4 (Performance) or would one inspection report during the performance period be enough?
Only one report (from your most recent inspection) needs to be provided. The credit form is broken into Establishment and Performance sections for recertification projects, and it can be a little clunky at times.
My site has no stormwater management facilities. It is surrounded by natural vegetation/open space, and parts of the land has hills. (A reservoir is located close to the hills.) The ratio of open space to the building is almost 1:1.
Would we still qualify for this credit? If so, would Option 2 (LIDLow-impact development: an approach to managing rainwater runoff that emphasizes on-site natural features to protect water quality, by replicating the natural land cover hydrologic regime of watersheds, and addressing runoff close to its source. Examples include better site design principles (e.g., minimizing land disturbance, preserving vegetation, minimizing impervious cover), and design practices (e.g., rain gardens, vegetated swales and buffers, permeable pavement, rainwater harvesting, soil amendments). These are engineered practices that may require specialized design assistance.) satisfy this credit best? We have plenty of natural vegetation and hillsides next to our aquifer, but no engineered bioswales/detention ponds and such.
Based on what you describe, your project should be able to comply using the stormwater management calculator.
I’m working on a project in Russia and having a difficult time finding much information outside of typical monthly rainfall. I've seen a discussion on the NC forum regarding a suggested approach for an international NC project, but I'm wondering if anyone has a go-to calculation to help determine a 2 yr, 24 hr design storm intensity, if this information hasn't been calculated for a particular country.
We’ve seen international projects reference data provided by a government agency. Someone on the project team might know which agency in Russia would have this information.
Also, there's an FAQ above that could be useful.
We plan to use storage tanks for rainwater collection, then re-use the water in our cooling tower and possibly toilets. Do i need to meter the outflow to the tower, or is it even necessary to provide proof of the re-use application?
You need to quantify the amount of runoff generated by your site, the amount you are capturing, and then the amount of water you are reusing.
I am working to get the EBOMEBOM is an acronym for Existing Buildings: Operations & Maintenance, one of the LEED 2009 rating systems. SSc6 v2009 credit. The building has already received the credit for NC v2.2 SSc6.1 and SSc6.2. I have the documentation for the previous version and credits.
1. Can I use these documents for the option 2 and just upload the previous credit template and documents that show that the runoff is mitigated by 90%?
2. If I can't follow option 2, do I need to perform all the calculations for option 1 since I'm not a PE?
You can provide the official USGBC/GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). scorecard showing that the project previously earned the Stormwater Design: Quantity Control credit. There’s no need to provide the documentation from the NC submittal.
Does anyone know how a field covered with solar panels would factor into the stormwater calculation? My though is that rainwater would run off of the pv arrays onto the ground and might have a little impact on the overall run off volume. Would there be a specific runoff coefficient to use in this case? Any input would be appreciated. Thanks!
I saw a presentation on this very topic about 2 years ago. I can't recall exactly what they determination regarding a CN was, but I think they did conclude it should increase.
Let me see if I can find my notes.
Link to the presentation summary is halfway down the page. Model it as if the panels weren't there, basically. This was a PA DEP presentation.
I am wondering if we can leave the sections below blank on the Stormwater Inspection Checklist due to only having large open turf/landscape areas and no retention ponds (we have ponds, but these are all sealed aside from a drain at the bottom with plastic filters to stormwater drains):
1.) Detention/Retention Management (SITE-SPECIFIC)
2.) Infiltration Facilities Managements (SITE-SPECIFIC)
3.) Filtration Practices (SITE-SPECIFIC)
Basically, I was going to put N/A in the sections above.
The roof rainwater drains into the ponds to fill them, but not for filtration purposes.
I have always avoided this credit, however, I thought i would take a stab at it. Hopefully, my lack of knowledge and background about stormwater won't prevent me from understanding what is required.
I am having a hard time envisioning your stormwater "pond." If it is an underground system, where any problems may not be immediatley apparent, that is all the more reason to perform, at minimum, a visual inspection of the system after larger storms.
There are about eight ponds that all feed into each other (like the Great Lakes between Canada and U.S. and the St. Lawrence Seaway). The water does not actually drain off of the site, they keep their levels even based on how much/little rainfall we receive. If there is not enough, the irrigation is turned on manually. If there is too much, we hope there isn't an overflow (we have an on-site person that watches it). The ponds evaporate 1-2"/day depending on the weather. In the rainy season, the rainwater from the roofs (4 buildings) filters through stones and grassy sections and flows into the ponds, therfore, no need to turn the irrigation lines on to raise the pond levels. Unfortunately, the rainwater comes when we don't really need it (wet season). The ponds all have a drainage system and the plastic filters between the ponds are cleaned as needed (bi-annually). Maybe these ponds are irrelevant because the water never actually leaves the site to go to the stormwater drains off-site? Basically, all of the rainwater stays on site, and we add water for irrigation and raising the pond levels. I do not have a "plan" that shows or proves this, just an older Landscaper that explained how it works. No way to prove this.
The ponds all have cement bottoms that are sealed aside from the drianage pipes between them.
Anyway, I am either way on or way off track here. I think it is a good concept though!
I think I get the gist of it. I would not leave everything blank, summarize what you just told me. Add a little bit about maintenence of the stone filter (cleaning sediment, trash, etc)....you clean the filters bi-annually, you inspect after every significant rainfall...
I've been reading the EB&OM stress test, and felt confused about the "You may get dirty" factor in SSc6. Does it mean if I achieve this credit, it will have a negative environmental impact on the building? Then will this kind of reason affect the target credit selection?
Jun, that factor is partly meant as a fun thing. All it means in this context is that you may have to go outside and get your hands dirty understanding and maintaining your stormwater system to earn the credit. Earning the credit should have a positive impact, and is recommended.
I am trying to verify that the cisterns on site release stormwater quickly enough to capture 2-year 24-hour design storm events by calculating the minimum drawdown rate. However, I cannot figure out what the rainfall event interval is. Is this information that I should be able to find or something that needs to be calculated?
I assume you are talking about back to back storm events here.
This topic comes up a lot in stormwater management, especially with capture and reuse. Calculating back to back events is a complex study, and requires the EPA's SWMM software. However, I don't believe you are being asked to get this involved for LEED.
I have never received clear guidance on how quickly we need to free up volumes for back to back storm events. However I have successfully made the case to the DEP, just last week, that a theoretical 2 yr storm event only occurs every 2 years, and therefore providing volume for back to back events is unrealistic.
I've also come across agencies wanting the water gone in 72 hours.
As farFloor-area ratio is the density of nonresidential land use, exclusive of parking, measured as the total nonresidential building floor area divided by the total buildable land area available for nonresidential structures. For example, on a site with 10,000 square feet (930 square meters) of buildable land area, an FAR of 1.0 would be 10,000 square feet (930 square meters) of building floor area. On the same site, an FAR of 1.5 would be 15,000 square feet (1395 square meters), an FAR of 2.0 would be 20,000 square feet (1860 square meters), and an FAR of 0.5 would be 5,000 square feet (465 square meters). as LEED is concerned, I would follow your local water quality requirements for drawdown, provide the necessary calculations that show all your reductions, and go from there. Show that you have an adequate bypass in place, in the event the cistern is full as well
I see that equation 3 in the reference manual performs the calculation for Q, the peak runoff rate, but I do not see how this value is used to calculate the amount of water retained on site.
How do you take the storm intensity calculated based on NOAA data and calculate the design storm rainfall volume?
Once rainfall volume has been calculated, how do you apply the runoff rate in order to calculate the amount of water mitigated on site?
My project does not currently have any special detention facilities in place, and I would like to assess our liklihood of acheiving this point. It seems to me that the reference manual provides very little support for calculating the volume of runoff using equation 3, is this a valid option?
TR-55 has all the methodology explained to calculate a runoff volume.
My project is pursuing Option 1, stormwater assessment report, of the Full documentation option of the O&M submittal path (what a mouthful!) of SSc6.
The site was designed to infiltrate the stormwater volumes created by a 100 year storm, so has the capacity to infiltrate all volumes created by the 2 year storm.
I'm entering the same volumes into the "Two year, 24 hour design storm onsite rainfall volume" and the "Mitigated design storm rainfall volume." When I do this the calculator (Both on the downloadable form and the LEEDonline version) says that the site mitigates 1% of the design storm rainfall volume. It seems like this should read 100%.
Is this a bug or am I totally missing something?
I haven't personally documented this credit in this way, but I would agree the form's response is puzzling. I would contact GBCIThe Green Building Certification Institute (GBCI) manages Leadership in Energy and Environmental Design (LEED) building certification and professional accreditation processes. It was established in 2008 with support from the U.S. Green Building Council (USGBC). to get further clarification.
At an office park, the stormwater management control is a large retention pond that is managed by an aquatic service vendor. They provide inspection logs for the LEED documentation. Recently, they recommended adding sterile carp to control an outgrowth of vegetation.
1)How and where is the best place to document this?
On one hand, it is part of the maintenance of our stormwater control (SSc6).
On the other hand, it is an organic and low-impact maintenance of the landscape and pest control (SSc3).
2) Is it worth exemplary performanceIn LEED, certain credits have established thresholds beyond basic credit achievement. Meeting these thresholds can earn additional points through Innovation in Design (ID) or Innovation in Operations (IO) points. As a general rule of thumb, ID credits for exemplary performance are awarded for doubling the credit requirements and/or achieving the next incremental percentage threshold. However, this rule varies on a case by case basis, so check the credit requirements. because of a synergy among credits?
The carp themselves do not contribute to SSc6 since they are performing a maintenance function unrelated to stormwater quantity control. It probably falls under SSc3, but may go beyond what is standard there.
I suggest reposting your inquiry under SSc3.
Looking for Precipitation Intensity. New NOAA Site lets me select Precipitation Intensity and location and a site, but doesn't return any data. Old site returns data but the list of available observation sites is unfamiliar to me. How can I locate nearest observatory to my subject property? Thanks in advance.
I don't know if you are still having trouble with the NOAA website, but the HDSC (http://hdsc.nws.noaa.gov/hdsc/pfds/index.html) has data on most states by weather station.
Does installation of mechanical filter media into the storm drain help meet this requirement? (Flogard curb filter inlet)
Mechanical filtration can improve the water quality, but doesn't typically reduce the quantity of runoff during the storm event, which this credit requires. Projects typically achieve this credit with one or more strategies for detention (stormwater ponds, cisterns, large planted areas or green roof), infiltration into the ground (pervious paving, drywells, landscaping) or collection and storage of the water for on-site uses such as irrigation or toilet flushing. Hope that helps.
I'm unclear as to how we show a reduction in stormwater runoff. I see how we calculate the current runoff by figuring the area type and using the formula given, but what does that get compared to?
Emily, you need to find opportunities for onsite stormwater mitigation—giving you a plan to compare your preexistingh runoff to.
In the Volume Captured equation the variable "I" is said to stand for percent impervious of surface. Is this the same thing as the coefficients or is this different? I thought it could mean 2 other things; one being that if 68% of a certain area was impervious then you would put .68. The other option would be that the surface type is 68% impervious so it rejects 68% of all water...which this could actually be the same theory behind the coeffecients. Anyone know?
Generally, when we calculate runoff, we use a runoff coefficient, or in the case of a site with multiple types of surfaces (pavement, grass, gravel, etc.) we calculate the areas of each surface and use a table that provides us with runoff coefficients for each type of surface. Then we develope a combined run-off coefficient value for the site or drainage that can be used with the Rational MethodA formula that can be used for calculating stormwater flow rates. Q = CIA, where C represents a coefficient for physical drainage area, I is the rainfall intensity, and A is area. The method is suitable for watersheds smaller than 300 acres in size.. In the case of storage volume, LEED provides us with an emperical method that essentially calculates the runoff coefficient (Volume of captured runoff) and the "I" stands for the percent of impervious area, as a whole number in the equation. In my opinion, I would rather use a combination of runoff coefficient values and their associated areas to develop a more accurate combined ronoff coefficient volume. This is the same runoff coefficient that is used for the Rational Method. The difference is that you are just calculating a simple volume for storage based on a given rainstorm over an entire area, assuming the surface is impervious, or it isnt, using the LEED storage equation. Runoff coefficients can be easily obtained for various surfaces from the internet.
I have 3 parking lots which are comprised of gravel (chat)....what would the coefficient for this be? I believe it should be less than any kind of pavement but more than grass.
Steve, I'd say this is highly variable. It would depend a lot on the type and size of gravel, and the characteristics of the sub-base. I think you have the right idea, but obviously that leaves a lot of variability.
Our project site is a winery that directs stormwater to ponds which are later used for irrigation. The only thing is that the ponds are sometimes considerably distant from the LEED building. Would we need to expand our LEED boundary to include the ponds? Does the water storage need to take place on site?
Prudence, have you reviewd the MPR supplemental guidance? I think you will find your answer in there. Please post back with further thoughts and questions.
1) How do we consider pools in this credit?
2) If so, how doe we account for runoff coefficient?
I consider a pool the same as a pond or lake. If the pool can contain the rainfall event with no discharge to the sanitary sewer, then the runoff coefficient is essentially zero. If, on the other hand, the rain that falls directly into the pool raises the water level sufficientl6y to overflow into the sanitary sewer, the runoff coefficient is 1.0. Many times the pool will have a bit of freeboard before the water level rises enough to overflow and this will allow you to capture the rainfall, and even make up for some evaporation that would otherwise be made up using potable waterWater that meets or exceeds U.S. Environmental Protection Agency drinking water quality standards (or a local equivalent outside the U.S.) and is approved for human consumption by the state or local authorities having jurisdiction; it may be supplied from wells or municipal water systems.. Much depends on the overflow elevation compared to normal water elevation and the elevation at which makeup water is introduced into the pool to make up for evaporation..
we adapted a vegetated area nearby our project space. i wonder the collected stormwater can be used as irrigation towards this new habitat?
because we would like to make use all our 15% captured stormwater runoff. .
Absolutely, use of captured rainwater for irrigation is a great thing, and contributes to other credits as well.
I am not seeing a default coefficient for pervious concrete or grid pavers. Can you use half of the default for pavers?
The coefficient depends on the kind of pavers.
I would say a "grasscrete" paver with 1/3 vegetation and 2/3 concrete would have a weighted average of 0.66(0.95*2/3 + 0.10*1/3).
Pervious concrete or pavers filled with gravel would be more similar to brick (0.85) in terms of overall permeability.
Amy, How did you come up with a coefficient of 0.85 for pervious concrete? While there can be a great deal of variablility between materials in market areas, the normal range is 500 - 200+ inches per hour permeability. This would seem to equate much closer to zero than to 0.85. Is there testing data that can be required? ASTMVoluntary standards development organization which creates source technical standards for materials, products, systems, and services C 1707 is a permeability test for pervious concrete used to determine when maintenance is required.
0.85 is the runoff coeffecient for brick pavement listed in the reference guide.
For most products I assume that testing data isn't required, but if you are using something that greatly exceeds the permeability expectations of similar products you may wish to provide supporting documentation.
Can you please tell me what the difference is between the percentage listed as "Percentage of storm rainfall volume mitigated" and the second percentage "Design storm rainfall mitagted" ?
I assume you are referring to the two tables on the Credit Form on LEED Online, correct? (the version of the form I am looking at has slightly different wording.)
If so, it is my understanding that table 2.1 is related to volume while table 2.2 is for runoff rate.
there is a question post by our client, and i did not have a definite answer for it. therefore would like to get some advice from here.
the storm water which been collected will be use for irrigation purposes. as to do the irrigation, our client thought of tapping a pipe from the stromwater tank and at the end of the pipe , add a faucet. every day, the gardener will use a long hose , tap onto the faucet and use the collected water for irrigation.
do you think , this concept will be acceptable by usgbc?
James, this is an okay strategy from USGBC's standpoint. To earn SSc6, though, you should focus not on the irrigation system, in my opinion, but in how much stormwater you're capturing from the site, and documenting that.
Would like to know, is 3 days is a default value in all design storm interval?
i unable to locate the interval value because is not stated in the central weather bureau here in Taiwan.
if 3 days is not a default value, what other ways i could calculate the interval value. is there anyone have this issue before?
could you share your thought and sample of calculation.
I'm not sure I totally understand your question, but the 2-year 24 hour design storm is usually shown as either the volume for the entire 24 hour period, or as the average inches per hour over the 24 hour period.
The form wants me to upload documentation of the most recent inspection. My site has no stormwater management facilities - its just a flat site with grass. Do I just need to (annually?) confirm that there have been no changes?
A flat site with grass is a stormwater management facility that according to the credit requirements does need inspection. It could be a pretty simple inspection.
If there were some massive deluge that eroded the grass and led to increased runoff to a local waterway, etc., you would want to be on top of that—so the inspection is that all that frivolous.
Green roofs help retain stormwater and reduce peak flow.
Use this step-by-step guide to find the data you need for this credit.
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