New developments in many jurisdictions must demonstrate “No Adverse Impact” (NAI) in drainage studies before they can get construction permits. City and county engineers want to know the development won’t harm others before they approve plans. But what does “No Adverse Impact” really mean? It depends on the jurisdiction.
Meaning Varies
Most jurisdictions require that new developments won’t add to flooding. In Montgomery County, for instance, developers do this by comparing runoff pre- and post-development. If engineers can show that post-development runoff does not exceed pre-development runoff, then they get their permit.
Such studies focus primarily on water surface elevations. But the Association of State Floodplain Managers (ASFPM) has a much broader definition.
In their book, No Adverse Impact means that actions of any community or property owner, public or private, “should not adversely impact the property and rights of others.”
An adverse impact can be measured by an increase in flood stages, flood velocity, flows, the potential for erosion and sedimentation, degradation of water quality, or increased cost of public services.
ASFPM
Definition Should Apply Beyond Floodplain
According to ASFPM, “No Adverse Impact” floodplain management extends beyond the floodplain to include managing development in the watersheds where floodwaters originate. NAI does not mean no development. It means that any adverse impact caused by a project must be mitigated, preferably as provided for in the community or watershed-based plan.
Flood losses are increasing by $6 billion annually. That’s because current policies promote intensification in high risk areas. They ignore changing conditions, undervalue natural floodplain functions, and often ignore adverse impacts.
Even if we perfectly implemented current standards, damage will increase.
Floodplains change due to filling.
Current regulations deal primarily with how to build in a floodplain vs. how to minimize future damages.
NAI actually broadens property rights by protecting those adversely impacted by others.
Trends in case law show that Act of God defenses have been greatly reduced due to ability to predict hazards events.
Hydraulic models facilitate proof of causation.
Use of sovereign immunity has been greatly reduced in lawsuits.
Communities are most likely to be held liable not when they deny a permit, but when they permit a development that causes damage to others.
NOAA’s Atlas-14 rainfall probabilities for this area show that’s about a 5-year rain.
NOAA’s Atlas-14 Rainfall Probability standards for the Lake Houston Area.
But rising floodwaters cut off large parts of Plum Grove – including escape routes. The new elevated City Hall nearly flooded again even though it’s far above the 100-year floodplain.
Photo from evening of 1/8/2022 courtesy of Plum Grove VFD after about six inches of rain.
As far as I can tell, 2004 Liberty County Subdivision Rules do not require “no adverse impact” for new developments. However, they do stipulate that “All roads and streets shall be designed to convey a 10-year storm event and not more than 6″ of water over the road in a 100-year storm event.”
Looks like the engineers missed all of those targets! This is a good example of why all jurisdictions should specify No Adverse Impact in their drainage regulations.
Posted by Bob Rehak on 1/20/22
1605 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/2020/12/20201207-Aerial-Dec-2020_851.jpg?fit=1200%2C800&ssl=18001200adminadmin2022-01-20 22:38:032022-01-21 09:09:20What Does “No Adverse Impact” Really Mean in Drainage Studies?
This proposal attempts to establish new rules for the Equity Prioritization Framework adopted by commissioners in 2019 and changed several times since. These new rules were provided to Task Force members only within the last few days even though the document is dated December 14, 2021, more than a month ago.
The rule changes apply mostly to the distribution of Trust Fund money established to supplement the flood bond if partner funding did not materialize as expected. However, the proposed changes could affect the distribution of flood bond funds that voters approved by 86% in 2018.
Proposal #1:
Place more emphasis on number of people, using structures as a proxy for people. Benefit = efficiency.
Observation:
This may disadvantage LMI neighborhoods as those projects tend to cost more and the neighborhoods have more apartments. They also have large numbers of homes crowding channels and floodplains. So, buyout costs will be higher. And historically, buyouts cost almost as much as construction. Also, apartments cost far more than single family homes. We need time to look at data on this.
Proposal #2:
Potential partner funding should not be considered in prioritization for use of trust funds.
Observation:
What if you could make trust fund dollars go nine times further? Typically, HUD grants require only a 10% match.
Proposal #3:
Use trust funds for projects, like street flooding, not even mentioned in the bond.
Observations:
The County proposes using FEMA damage data back to 1977 to determine “Existing Level of Service.” This is a blatant attempt to tilt the playing field toward the inner city. In 1977, Beltway 8 and Intercontinental airport were still under construction. US59 was a 2-lane blacktop road. Outlying neighborhoods like Kingwood barely existed. This makes it impossible for any outlying neighborhoods to qualify for help with Trust Funds.
Choosing 1977 as the starting point ignores 45 years of flood mitigation spending totaling approximately $5 billion.
We don’t have enough money in the trust fund to complete all the bond projects. So, if we spend trust fund money on projects not in the bond – without partner help – it will mean cancelling bond projects somewhere else.
Implementing this proposal will make it very difficult to get voters to approve future flood bonds.
Street flooding is often caused by blocked drains. Rains can’t get to channels and streams. Fixing ditches has historically been the job of cities and precincts. HCFCD funds have focused on channels and streams. Street ditches were never mentioned in the bond.
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2022/01/MultiBlockages.jpg?fit=1440%2C960&ssl=19601440adminadmin2022-01-19 10:46:072022-01-19 16:01:41Harris County Making Another Attempt to Shift Flood Mitigation Funds
Lakewood Cove residents reported yesterday and today that contractors at the Laurel Springs RV Resort are pumping stormwater from their detention pond into Precinct 4’s Edgewater Park. The reports are true. And it’s a permit violation.
I also found contractors bringing in fill from the outside that I thought was going to be “cut” from the detention pond. All photos below were taken on 1/18/22.
Pumping From Pond onto Neighboring Property
The approved permit plans clearly state that “Stormwater runoff shall not cross property lines.”
Stamp on many pages of approved Laurel Springs RV Resort plans.
I guess at some point the water in the pond ceased being runoff. Now it’s just a nuisance. The plans said pond water would be pumped into the City storm sewers. Hmmmm.
Photographed from Laurel Springs Lane looking west.
Here’s an aerial photo looking toward Laurel Springs Lane.
Check out all the muck being washed into the woods. Those woods belong to Harris County Pct. 4. That’s part of new Edgewater Park.
Note the lack of silt fences in the two photos above. Plans clearly state that silt fences will be installed to keep silt from escaping the property. Double Hmmmm!
Bringing in Fill instead of Moving It From Within the Site
As I photographed the pumping, I noticed a parade of dump trucks bringing in fill, dumping it, and leaving as a bulldozer spread it out and another machine quickly compacted it.
Looking NW toward Lowes in top center. Note dump truck depositing fill – one of many that I watched.The area where they deposited fill just north of the pond corresponds to the plans. See below.
From text on the image above, I assumed that the job was to be a routine “cut and fill” operation. Maybe I shouldn’t have assumed.
Cut and Fill is an industry standard in floodplains. It means you move dirt from one part of the site to another. So, there is no additional fill brought into the floodplain. The fill area above appears to be in the .2% annual chance floodplain, according to the old FEMA map below. However, the developer did not mark the .2% chance floodplain on plans.
FEMA floodplain map. Aqua = 1% annual chance. Brown = .2% annual chance.It appears the northern part of the detention pond (not shown on this old satellite image) cuts between the aqua and brown areas.
For the record, Chapter 19 of Houston’s Code of Ordinances currently does not prohibit bringing fill into the .2% annual chance floodplain. See Section 19.34.
Posted by Bob Rehak on 1/18/2022
1603 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/2022/01/20220118-DJI_0490.jpg?fit=1200%2C799&ssl=17991200adminadmin2022-01-18 20:33:432022-01-18 20:40:31RV Resort Pumping Stormwater Into Edgewater Park, Bringing in Fill
What Does “No Adverse Impact” Really Mean in Drainage Studies?
New developments in many jurisdictions must demonstrate “No Adverse Impact” (NAI) in drainage studies before they can get construction permits. City and county engineers want to know the development won’t harm others before they approve plans. But what does “No Adverse Impact” really mean? It depends on the jurisdiction.
Meaning Varies
Most jurisdictions require that new developments won’t add to flooding. In Montgomery County, for instance, developers do this by comparing runoff pre- and post-development. If engineers can show that post-development runoff does not exceed pre-development runoff, then they get their permit.
Such studies focus primarily on water surface elevations. But the Association of State Floodplain Managers (ASFPM) has a much broader definition.
In their book, No Adverse Impact means that actions of any community or property owner, public or private, “should not adversely impact the property and rights of others.”
Definition Should Apply Beyond Floodplain
According to ASFPM, “No Adverse Impact” floodplain management extends beyond the floodplain to include managing development in the watersheds where floodwaters originate. NAI does not mean no development. It means that any adverse impact caused by a project must be mitigated, preferably as provided for in the community or watershed-based plan.
Here’s a presentation that covers NAI at a high level. Some key points include:
Where to Find More Information About NAI
ASFPM has extensive information on the guidelines for “no adverse impact.” They include NAI How-to Guides For…
This 108-page PDF from ASFPM sums it all up in one easy-to-download file.
Recent Case Study of Adverse Impact
Earlier this week, I toured Plum Grove to survey flood damage from the January 8/9 rains.
NOAA’s Atlas-14 rainfall probabilities for this area show that’s about a 5-year rain.
But rising floodwaters cut off large parts of Plum Grove – including escape routes. The new elevated City Hall nearly flooded again even though it’s far above the 100-year floodplain.
Local residents and city officials attribute their flooding woes to largely unmitigated development in nearby Colony Ridge. The City is currently suing the developer.
Flooding two weeks ago was so bad that the Plum Grove Volunteer Fire Department sealed off roads and warned people to stay out. Currents were reportedly moving fast enough to sweep cars off roads.
As far as I can tell, 2004 Liberty County Subdivision Rules do not require “no adverse impact” for new developments. However, they do stipulate that “All roads and streets shall be designed to convey a 10-year storm event and not more than 6″ of water over the road in a 100-year storm event.”
Looks like the engineers missed all of those targets! This is a good example of why all jurisdictions should specify No Adverse Impact in their drainage regulations.
Posted by Bob Rehak on 1/20/22
1605 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.
Harris County Making Another Attempt to Shift Flood Mitigation Funds
Harris County is making another attempt to shift flood mitigation funds from outlying neighborhoods toward the city center. Here’s the latest proposal that will be considered by the Community Resilience Flood Task Force at a noon meeting today.
Key Concerns About Proposal
This proposal attempts to establish new rules for the Equity Prioritization Framework adopted by commissioners in 2019 and changed several times since. These new rules were provided to Task Force members only within the last few days even though the document is dated December 14, 2021, more than a month ago.
The rule changes apply mostly to the distribution of Trust Fund money established to supplement the flood bond if partner funding did not materialize as expected. However, the proposed changes could affect the distribution of flood bond funds that voters approved by 86% in 2018.
Proposal #1:
Place more emphasis on number of people, using structures as a proxy for people. Benefit = efficiency.
Observation:
This may disadvantage LMI neighborhoods as those projects tend to cost more and the neighborhoods have more apartments. They also have large numbers of homes crowding channels and floodplains. So, buyout costs will be higher. And historically, buyouts cost almost as much as construction. Also, apartments cost far more than single family homes. We need time to look at data on this.
Proposal #2:
Potential partner funding should not be considered in prioritization for use of trust funds.
Observation:
What if you could make trust fund dollars go nine times further? Typically, HUD grants require only a 10% match.
Proposal #3:
Use trust funds for projects, like street flooding, not even mentioned in the bond.
Observations:
How To Be Heard
Here is a presentation that the Community Resilience Flood Task Force will review at noon today. It provides a little more detail than the County Administrator’s description.
If this proposal concerns you, please send your comments to: CFRTFpubliccomment@gmail.com.
To view the meeting online, register at Cfrtf.harriscountytx.gov. It goes from 12-2 today.
Posted by Bob Rehak on 1/19/2022
1604 Days since Hurricane Harvey
RV Resort Pumping Stormwater Into Edgewater Park, Bringing in Fill
Lakewood Cove residents reported yesterday and today that contractors at the Laurel Springs RV Resort are pumping stormwater from their detention pond into Precinct 4’s Edgewater Park. The reports are true. And it’s a permit violation.
I also found contractors bringing in fill from the outside that I thought was going to be “cut” from the detention pond. All photos below were taken on 1/18/22.
Pumping From Pond onto Neighboring Property
The approved permit plans clearly state that “Stormwater runoff shall not cross property lines.”
I guess at some point the water in the pond ceased being runoff. Now it’s just a nuisance. The plans said pond water would be pumped into the City storm sewers. Hmmmm.
Note the lack of silt fences in the two photos above. Plans clearly state that silt fences will be installed to keep silt from escaping the property. Double Hmmmm!
Bringing in Fill instead of Moving It From Within the Site
As I photographed the pumping, I noticed a parade of dump trucks bringing in fill, dumping it, and leaving as a bulldozer spread it out and another machine quickly compacted it.
From text on the image above, I assumed that the job was to be a routine “cut and fill” operation. Maybe I shouldn’t have assumed.
Cut and Fill is an industry standard in floodplains. It means you move dirt from one part of the site to another. So, there is no additional fill brought into the floodplain. The fill area above appears to be in the .2% annual chance floodplain, according to the old FEMA map below. However, the developer did not mark the .2% chance floodplain on plans.
For the record, Chapter 19 of Houston’s Code of Ordinances currently does not prohibit bringing fill into the .2% annual chance floodplain. See Section 19.34.
Posted by Bob Rehak on 1/18/2022
1603 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.