One third of Harris County is now impervious cover. According to the Harris County Infrastructure Resilience Team, green roofs are one of several tools that can help mitigate flooding by converting impervious cover back into green space.
Also known as ‘vegetated roofs’ or ‘living roofs,’ they can reduce runoff by soaking up part of the rainfall during a storm and holding it back.
Part of 19,200 square foot green roof installed on EPA headquarters in Denver
Green roofs consist of a waterproofing membrane, growing medium (soil) and vegetation (plants) overlying a traditional roof.
The U.S. General Services Administration (GSA) manages more than 2 million square feet of green roofs. Some date back to the 1930s. So, they have extensive experience.
GSA points out that “Most urban and suburban areas contain large amounts of paved or constructed surfaces which prevent stormwater from being absorbed into the ground. The resulting excess runoff damages water quality by sweeping pollutants into water bodies. Green roofs can reduce the flow of stormwater from a roof by up to 65% and delay the flow rate by up to three hours.
Green roofs mimic natural hydrological processes as part of a watershed management approach to drainage. They are just one of many tools to reduce impervious cover.
Cost/Benefit Analysis Shows Payback
Cost/benefit analysis shows that green roofs can provide payback in 6.2 years. Their longevity has the greatest effect on savings.
They last twice as long as conventional roofs.
U.s. General services administration
Of course, they cost more to install and maintain. But GSA says that the other benefits they provide (stormwater and energy reduction) more than compensate for the premium owners pay.
But any cost/benefit analysis for owners/investors depends on many factors, such as the square footage and height of buildings. Energy and stormwater management benefits increase with size of a roof. Energy savings primarily benefit the higher floors in a multi-story building, i.e., those closest to the roof.
GSA notes that any increased market value of buildings with green roofs was not included in its cost/benefit analysis. GSA believes that if it were, it would show even greater benefit.
Benefits to Owners AND Community
Regardless, even though they provide a positive payback to owners, benefits to the community have the greatest positive impact. They provide net present value savings of almost $38 per square foot of roof, according to the GSA.
It is important that green roofs have a suitable drainage path for excess water that is not absorbed during larger storms. All green roofs should be designed to move excess water away from the building. This water can then be directed to rain gardens or cisterns.
However, green roofs won’t work for everyone. The increased weight requires additional structural support. And the slope must be gentle. They’re primarily for flat or slightly sloping roofs. All those factors make retrofitting them to pre-existing buildings difficult. Generally, engineers must plan for them before construction of a building.
Posted by Bob Rehak on 1/14/23, first in a series on green infrastructure
1964 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2023/01/20230114-Screenshot-2023-01-14-at-6.25.25-PM.jpg?fit=1200%2C680&ssl=16801200adminadmin2023-01-14 18:29:142023-01-14 18:52:11Green Roofs Help Reduce Runoff and Energy Use
On October 28, Royal Pines flooded a neighbor on less than an inch of rain. Two months later, on December 29th, the same thing happened again. The video below provided by the homeowner shows the volume of water funneled across her property by the developer.
Video from NW corner of Royal Pines
This video and the previous one from October demonstrate the dangers of clearcutting and redirecting drainage without first constructing sufficient stormwater detention capacity.
The homeowner who shot the video lives adjacent to the left border in the photo below. Royal Pines has apparently sloped its property toward that corner where contractors will eventually build a stormwater detention basin.
Looking N across Royal Pines. This and other photos below taken on 1/3/23.
Land now slopes toward where video was filmed at left corner. But that area used to slope in the opposite direction. See details below from the USGS NATIONAL MAP and the developer’s plans.
Green arrow on left shows location of homeowner’s property. Red X within V-shaped contour shows exact location of low point (graph on right) before clearing and grading the land.
There used to be an 8-foot drop east of the homeowner’s property. But now, instead of water flowing directly north to White Oak Creek, it flows northwest.
The general plan for Royal Pines (below) shows the same V-shape in the proposed detention basin (upper left). The line represents the edge of the floodplain and confirms that the developer A) knew about the slope and B) changed it.
Royal Pines General Plan.
Silt Fence, Trench Ineffective Against That Much Water
The video above and the photos below show that silt fence makes a terrible dam against even small rains funneling toward a point from such a large area.
Exercise in futility. A series of silt fences have done little to catch and slow the water...or the silt. Note erosion deposited in woods.Looking south. The developer apparently tried to divert runoff racing toward the homeowner with a trench. But erosion from the barren land rapidly filled it in. Runoff also collects at the entrance to Royal Pines. Looking ENE from the entrance at the northern end of West Lake Houston Parkway.
Unfortunately, the developer plans to build homes there, not another detention basin.
0.88 Inches of Rain Fell in Two Hours
The graph below from the Harris County Flood Warning System shows that .88 inches of rain fell in the two afternoon hours before the homeowner shot the video.
Homeowner shot video after first two bars on left.
The table below shows that that much rain in two hours constitutes less than a 1-year rainfall event.
Atlas 14 rainfall probabilities for this area.
That’s consistent with actual observed events and climate records. According to the National Weather Service, on average, we can expect rainfalls greater than 1 inch 14 times per year in Houston. That’s about once per month.
Woodridge Village Revisited
The Montgomery County Engineer’s Office has reportedly asked the developer’s engineering company to revise its plans. The homeowner says that according to the engineer’s office, not even a 6-7 foot tall berm around that portion of the property would be enough to stop all the water flowing in that direction.
So, what lessons can we learn from this example? As with Woodridge Village, don’t clear and grade this much land before constructing detention basins!
The first sentence of Section 11.086 of the Texas Water Code states that “No person may divert … the natural flow of surface waters in the state, or permit a diversion … to continue, in a manner that damages the property of another…”
Posted by Bob Rehak on 1/13/2023
1963 Days since Hurricane Harvey
The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2023/01/Keyframe-Royal-Pines-Flood-2.jpg?fit=1200%2C675&ssl=16751200adminadmin2023-01-13 10:01:062023-01-13 10:38:08Royal Pines Floods Neighbor on Less Than 1″ of Rain … AGAIN
On January 9, 2023, FEMA released a Simplified Procedures policy for Public Assistance grants to speed up recovery for applicants. Small projects are now defined as those up to $1 million.
The new policy should reduce administrative burdens and enable communities to recover more quickly after presidentially declared events by streamlining documentation requirements.
FEMA will accept estimates with summary information and the applicant’s certifications for damage and work, instead of requiring applicants to provide full or detailed documentation.
FEMA Press Release
FEMA conducted a review in 2020. It showed that if a $1 million threshold were applied, 94 percent of projects would be considered small and help put additional recovery dollars in the hands of applicants faster and accelerate closure of projects.
FEMA intends to continue adjusting the threshold annually to reflect changes in the Consumer Price Index. It also intends to review the base threshold every three years.
The new policy is not directly aimed at individuals, but at state and local governments and certain types of private nonprofit organizations. Public Assistance grants cover such things as:
Disaster-related debris removal
Emergency protective measures
Repairs to damaged or destroyed infrastructure (i.e., roads).
FM1010 Washout during Harvey at Rocky Branch in Plum Grove near the East Fork. Still not repaired after 5.5 years.
Depending on repair cost and other factors, the road washout above is an example of the type of project that might benefit from the new policy. However, it’s not clear whether the simplified procedures apply retroactively to damage from past disasters or only future disasters. More details will follow.
Applicant has legal responsibility to perform the work
Cost is reasonable.
Once FEMA and the state review and approve the government agencies’ or nonprofits’ RPAs, applicants work with their FEMA representative to develop a damage inventory.
FEMA obligates funds to the state once a project meets Stafford Act eligibility requirements. The state is the official recipient of FEMA federal assistance. The state is then responsible for disbursing the money to applicants.
FEMA will hold a series of webinars in coming weeks to explain more about the simplified policy. Additional details are not yet available.
Getting aid to people faster after a disaster is necessary. This is a very complex subject. I wish all forms of disaster relief, including hazard mitigation, could be simplified. We’re still waiting on the Harris County, the GLO and HUD to agree on a plan for spending $750 million in mitigation funds related to Hurricane Harvey – 5.5 years after the event!
Posted by Bob Rehak on 1/12/23 based on a FEMA Press Release
1962 Days after Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2020/10/20201025-DJI_0919.jpg?fit=1200%2C900&ssl=19001200adminadmin2023-01-12 13:04:432023-01-12 13:20:54FEMA Simplifying Procedures for Small Public Assistance Grants
Green Roofs Help Reduce Runoff and Energy Use
One third of Harris County is now impervious cover. According to the Harris County Infrastructure Resilience Team, green roofs are one of several tools that can help mitigate flooding by converting impervious cover back into green space.
Also known as ‘vegetated roofs’ or ‘living roofs,’ they can reduce runoff by soaking up part of the rainfall during a storm and holding it back.
Green roofs consist of a waterproofing membrane, growing medium (soil) and vegetation (plants) overlying a traditional roof.
Well-designed, engineered and maintained green roofs provide multiple environmental, social, economic, and aesthetic benefits. They help:
Can Reduce Runoff by up to 65%
The U.S. General Services Administration (GSA) manages more than 2 million square feet of green roofs. Some date back to the 1930s. So, they have extensive experience.
GSA points out that “Most urban and suburban areas contain large amounts of paved or constructed surfaces which prevent stormwater from being absorbed into the ground. The resulting excess runoff damages water quality by sweeping pollutants into water bodies. Green roofs can reduce the flow of stormwater from a roof by up to 65% and delay the flow rate by up to three hours.
Extensive green roofs intercept and retain the first 1⁄2 to 3⁄4 inch of rainfall, preventing it from ever becoming runoff.
Green roofs mimic natural hydrological processes as part of a watershed management approach to drainage. They are just one of many tools to reduce impervious cover.
Cost/Benefit Analysis Shows Payback
Cost/benefit analysis shows that green roofs can provide payback in 6.2 years. Their longevity has the greatest effect on savings.
Of course, they cost more to install and maintain. But GSA says that the other benefits they provide (stormwater and energy reduction) more than compensate for the premium owners pay.
The City of Houston provides tax abatements and discounts for green stormwater infrastructure, such as green roofs, in recognition of the stormwater management benefits. Such savings can also provide significant value for owners.
But any cost/benefit analysis for owners/investors depends on many factors, such as the square footage and height of buildings. Energy and stormwater management benefits increase with size of a roof. Energy savings primarily benefit the higher floors in a multi-story building, i.e., those closest to the roof.
GSA notes that any increased market value of buildings with green roofs was not included in its cost/benefit analysis. GSA believes that if it were, it would show even greater benefit.
Benefits to Owners AND Community
Regardless, even though they provide a positive payback to owners, benefits to the community have the greatest positive impact. They provide net present value savings of almost $38 per square foot of roof, according to the GSA.
Green roofs are being increasingly used in urban areas where space constraints limit the use of other stormwater management practices. Such roofs can protect the roofing materials below by shielding harmful UV rays and protecting them from adverse weather events.
Importance of Drainage Paths, Right Plants
It is important that green roofs have a suitable drainage path for excess water that is not absorbed during larger storms. All green roofs should be designed to move excess water away from the building. This water can then be directed to rain gardens or cisterns.
In Texas, such roofs require special plant selection that can hold up to the region’s extremes in heat and humidity.
Not for Everyone
However, green roofs won’t work for everyone. The increased weight requires additional structural support. And the slope must be gentle. They’re primarily for flat or slightly sloping roofs. All those factors make retrofitting them to pre-existing buildings difficult. Generally, engineers must plan for them before construction of a building.
Posted by Bob Rehak on 1/14/23, first in a series on green infrastructure
1964 Days since Hurricane Harvey
Royal Pines Floods Neighbor on Less Than 1″ of Rain … AGAIN
On October 28, Royal Pines flooded a neighbor on less than an inch of rain. Two months later, on December 29th, the same thing happened again. The video below provided by the homeowner shows the volume of water funneled across her property by the developer.
This video and the previous one from October demonstrate the dangers of clearcutting and redirecting drainage without first constructing sufficient stormwater detention capacity.
Altering Landscape Accelerates Runoff Toward Homeowner
The homeowner who shot the video lives adjacent to the left border in the photo below. Royal Pines has apparently sloped its property toward that corner where contractors will eventually build a stormwater detention basin.
Land now slopes toward where video was filmed at left corner. But that area used to slope in the opposite direction. See details below from the USGS NATIONAL MAP and the developer’s plans.
There used to be an 8-foot drop east of the homeowner’s property. But now, instead of water flowing directly north to White Oak Creek, it flows northwest.
The general plan for Royal Pines (below) shows the same V-shape in the proposed detention basin (upper left). The line represents the edge of the floodplain and confirms that the developer A) knew about the slope and B) changed it.
Silt Fence, Trench Ineffective Against That Much Water
The video above and the photos below show that silt fence makes a terrible dam against even small rains funneling toward a point from such a large area.
Unfortunately, the developer plans to build homes there, not another detention basin.
0.88 Inches of Rain Fell in Two Hours
The graph below from the Harris County Flood Warning System shows that .88 inches of rain fell in the two afternoon hours before the homeowner shot the video.
The table below shows that that much rain in two hours constitutes less than a 1-year rainfall event.
That’s consistent with actual observed events and climate records. According to the National Weather Service, on average, we can expect rainfalls greater than 1 inch 14 times per year in Houston. That’s about once per month.
Woodridge Village Revisited
The Montgomery County Engineer’s Office has reportedly asked the developer’s engineering company to revise its plans. The homeowner says that according to the engineer’s office, not even a 6-7 foot tall berm around that portion of the property would be enough to stop all the water flowing in that direction.
So, what lessons can we learn from this example? As with Woodridge Village, don’t clear and grade this much land before constructing detention basins!
The first sentence of Section 11.086 of the Texas Water Code states that “No person may divert … the natural flow of surface waters in the state, or permit a diversion … to continue, in a manner that damages the property of another…”
Posted by Bob Rehak on 1/13/2023
1963 Days since Hurricane Harvey
The thoughts expressed in this post represent opinions on matters of public concern and safety. They are protected by the First Amendment of the US Constitution and the Anti-SLAPP Statute of the Great State of Texas.
FEMA Simplifying Procedures for Small Public Assistance Grants
On January 9, 2023, FEMA released a Simplified Procedures policy for Public Assistance grants to speed up recovery for applicants. Small projects are now defined as those up to $1 million.
The new policy should reduce administrative burdens and enable communities to recover more quickly after presidentially declared events by streamlining documentation requirements.
FEMA conducted a review in 2020. It showed that if a $1 million threshold were applied, 94 percent of projects would be considered small and help put additional recovery dollars in the hands of applicants faster and accelerate closure of projects.
FEMA intends to continue adjusting the threshold annually to reflect changes in the Consumer Price Index. It also intends to review the base threshold every three years.
The new policy is not directly aimed at individuals, but at state and local governments and certain types of private nonprofit organizations. Public Assistance grants cover such things as:
Depending on repair cost and other factors, the road washout above is an example of the type of project that might benefit from the new policy. However, it’s not clear whether the simplified procedures apply retroactively to damage from past disasters or only future disasters. More details will follow.
How Public Assistance Usually Works
In general, applicants submit Requests for Public Assistance (RPAs) within 30 days of the disaster declaration. They must demonstrate that:
Once FEMA and the state review and approve the government agencies’ or nonprofits’ RPAs, applicants work with their FEMA representative to develop a damage inventory.
FEMA obligates funds to the state once a project meets Stafford Act eligibility requirements. The state is the official recipient of FEMA federal assistance. The state is then responsible for disbursing the money to applicants.
FEMA will hold a series of webinars in coming weeks to explain more about the simplified policy. Additional details are not yet available.
Getting aid to people faster after a disaster is necessary. This is a very complex subject. I wish all forms of disaster relief, including hazard mitigation, could be simplified. We’re still waiting on the Harris County, the GLO and HUD to agree on a plan for spending $750 million in mitigation funds related to Hurricane Harvey – 5.5 years after the event!
Posted by Bob Rehak on 1/12/23 based on a FEMA Press Release
1962 Days after Hurricane Harvey