The Great Lakes Dredge finally liberated the ditch that drains the western third of Kingwood 462 days after Harvey.
A new report by the Texas Water Conservation Association reviews the relative merits and problems with various flood mitigation strategies. The strategies include pre-release from reservoirs; on- and off-channel reservoirs; aquifer storage and recovery; and dredging. Anyone who wants to understand how professionals evaluate the merits of different strategies should read this concise, clearly written, 25-page report called Flooding in Texas: Preparation and Response.
About the Authors
The Texas Water Conservation Association is an association of water professionals and organizations in the state of Texas. Its members represent river authorities, municipalities, navigation and flood control districts, drainage and irrigation districts, utility districts, municipalities, groundwater conservation districts, all kinds of water users, and general/environmental water interests. Membership includes engineers, hydrogeologists, attorneys, government administrators, and numerous other individuals committed to Texas water resource management. Don’t be scared by the author’s titles.
Bias Toward Conservation over Mitigation
The only warning I have: the authors have an inherent bias toward water conservation as opposed to flood mitigation, as their name would imply. That said, it’s important for people who flooded to understand that flood control is not the main responsibility of people who operate dams. Water conservation is.
Three Types of Reservoirs
The report starts with a discussion of the three main types of reservoirs: water-supply, flood-control, and dual-purpose reservoirs. Lake Conroe and Lake Houston are both water-supply reservoirs. Texas has 150 such reservoirs, by far the most common type.
That section ends with this admonishment: “In water supply reservoirs, there is often very little storage available between maximum design impoundment and the top of the gates. This distance is sometimes referred to as freeboard and should not be considered extra storage, as it is unsafe to operate in that manner. A reservoir that attempts to indefinitely impound stormwater without an emergency spillway will eventually overtop at the lowest elevation across the dam, usually the top of the control gates. This kind of operation is dangerous as it jeopardizes the integrity of the dam, potentially resulting in a dam failure. For this reason, reservoir operators follow specific flood operation protocols to ensure that the dam is not breached.”
Four Main Mitigation Strategies Examined
A discussion of four main flood mitigation strategies follows.
Many people in the Houston area question why Lake Conroe did not release earlier during Harvey. Factors that influence whether prerelease may be of help or hurt include:
Predicted location and amount of rainfall in relation to a reservoir;
River-basin size and lag time;
Existing downstream flow;
Predicted weather conditions below a reservoir.
Direction of Approaching Storm is Crucial in Pre-Release
During Harvey, a factor that weighed heavily in the decision-making at the Lake Conroe Dam was the direction of the approaching storm. Because it approached from the Gulf, operators worried that pre-leasing water would overload downstream communities which already struggled with the local rainfall.
On the other hand, both the Memorial and Tax Day floods approached from the West or North. In those cases, pre-release was safer.
This section concludes with the observation that, “Harvey dumped approximately … 75 million acre feet of water. Texas’ statewide water conservation storage is approximately 31.5 million acre feet. … No amount of prerelease, and no amount of temporary or permanent conversion of water supply storage, would have appreciably reduced the magnitude of flooding caused by Hurricane Harvey.” And later, “Prerelease is a strategy with inherent risk, because the decision making regarding its use is based on imperfect predictions.”
On-Channel Reservoirs: A Proven Approach
Next, the report considers On-Channel reservoirs, such as Barker and Addicks. “On-channel reservoirs,” they say, “are an important component of the flood mitigation discussion, and have demonstrated effectiveness in multiple areas of the state. As an added benefit, on-channel reservoirs also provide an opportunity to double as a major water supply source, as many of the state’s dual-purpose reservoirs have done for decades.” Harris County Flood Control budgeted for these in its $2.5 million flood bond.
Off Channel Reservoirs Have Severe Limits
Off-Channel Reservoirs represent a less attractive alternative. Sand miners fondly point to the extra storage capacity in their pits for flood mitigation. However, the report points out that pumps can’t work fast enough to create meaningful reductions in flood levels. Other problems: very limited capacity, pumping costs, and debris floating in the water that could clog pumps.
Pros and Cons of Aquifer Storage and Recovery (ASR)
Many people have discussed the possibility of aquifer storage and recovery. It has proved to be a viable strategy for water supply. Managers pump excess water underground for storage in aquifers until needed for future use.
“Initial feasibility and pilot-testing studies are important,” say the authors, “as ASR requires the right physical conditions (e.g. geology, ground slope, groundwater quality) to be feasible. It also must be economically competitive with other viable options.”
“For ASR to have any meaningful impact in an extreme flooding event, extensive off-channel storage would be required, because the rate at which water could be injected underground is so slow in comparison to the rate of flood flows. As such, the off-channel storage is actually the mechanism for mitigating the flood in this case, not the ASR system.”
“As a flood control strategy, however, ASR cannot provide a first line of defense during an extreme storm event due to its need for extensive storage and treatment and its inability to compete economically with other solutions.”
Also, water treatment would be needed before pumping it into the ground because water quality in large flood events is extremely degraded.
When Dredging Helps
The report discusses many purposes for dredging and extensively references the Army Corps’ emergency project on the San Jacinto. It discusses dredging in rivers, streams, lakes, and ditches; for maintenance, navigation, and to remove blockages (like those we have); from cost, environmental, technical, and disposal points of view. Authors lament the expense of dredging but acknowledge its usefulness in certain cases.
Need for Single Source of Emergency Communication
Before closing, the reports also addresses the need for a consistent, focused communication protocol to warn people when flood gates will open. This section also discusses the regulatory environment that dam operators live within. In other words, the restraints that they face.
It concludes by saying that, “During a flood event, it is important that evacuation orders and flood warnings come from a single, designated source to avoid confusion and ensure accurate information for the public. In Texas, the leading notification providers are local Emergency Operations Centers (EOCs) and the National Weather Service (NWS). Reservoir conditions are one piece of the flooding puzzle and operators must provide real-time information to EOCs and the NWS so those entities can weigh all contributing factors to provide the best possible flooding information to the public.”
Look at Flooding from Professional’s Perspective
If you want to understand the world from a water-professional’s point of view, read this thought-provoking report. I didn’t agree with everything in it, but usually when I didn’t, it was because they were referencing another location, not ours. The author’s freely acknowledge that every watershed is unique and must be evaluated from its own perspective.
Posted on December 3, 2018 by Bob Rehak
462 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2018/12/GreatLakesAtRiverGrove-e1543893170224.jpg?fit=1500%2C236&ssl=12361500adminadmin2018-12-03 21:17:542018-12-03 21:21:14Texas Water Conservation Association Issues Report on Pros and Cons of Flood Mitigation Strategies
Some unexpected good news! The River Grove boat ramp could soon open…as early as next week. The Great Lakes Dredge is starting to chew its way through the massive side bar that has had Kingwood’s only boat dock shut down for 16 months.
The original speculation was that the Army Corps would leave River Grove alone until the rest of the job was complete. Corps officials told me that they worried about the safety of recreational boaters around the massive dredging equipment and pipelines.
Something must have changed because at 8 a.m. this morning, Bruce Casto snapped this shot on his cell phone. Bruce heard second hand from another person in the park that someone on the dredge yelled across the water that, “The boat dock will be open in a week.”
I try not to repeat rumors but I’ve known Bruce for a long time and trust him. And given the location of the dredge in this photo, there is a better than 50/50 chance that River Grove will soon open. I have not verified that yet with the Army Corps of Engineers because of the timing of this surprise (on the weekend).
Posted on 12/3/18 by Bob Rehak
461 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2018/12/Dredge-at-River-Grove.jpg?fit=1500%2C947&ssl=19471500adminadmin2018-12-02 18:22:522018-12-02 18:28:18River Grove Boat Ramp May Open Next Week
Researchers at Texas A&M Galveston and the University of Maryland have just published a massive new study on The Growing Threat of Urban Flooding: A National Challenge. The study – a treasure trove of insights – actually started in 2016, before Harvey.
It focuses primarily on urban flooding as opposed to riverine flooding, which caused many of the Lake Houston Area’s problems. However, area residents should not dismiss it. The two types overlap and the report largely addresses issues that exacerbate both, such as inadequate governmental systems, engineered structures and growth that overwhelms both.
The report contains eight major sections that quantify the scope of the challenge. Below, a few highlights from each.
I. Urban Floods: The Nation’s Hidden Challenge
Documents the stunning extent of urban flooding and factors that continue to make it worse. Did you know for instance, that two thirds of the nation’s population living in floodplains live in just two states: Texas and New York? Or that Texas led the nation in billion-dollar water and wind disasters between 1980 and 2018?
II. Analyzing Urban Flooding
Reveals statistics on the scope of the problem. Two gems:
Nationally, 83% of respondents indicated they had experienced urban flooding in their communities. And 85% experienced urban flooding outside special flood hazard areas!
III. Where Urban Flooding Occurs
Shows that Texas ranks in the middle of the pack in terms of frequency of events, as opposed to major events. The researchers found that nationwide, approximately 25% of all flood insurance claims are submitted by policy holders whose property lies outside the 100-year flood plain. New York found that “The problem in most communities is lack of enforcement. Communities need a comprehensive plan to address development, infrastructure needs, stormwater runoff, and building codes. When a community doesn’t address these issues it only exacerbates other problems and continued urban sprawl eats up rural areas causing flooding, erosion, and infrastructure malfunction.”
IV. Why Does Urban Flooding Happen?
Examines aging and inadequate drainage systems, increases in local and regional runoff, sewage and stormwater backups, changes in local physical conditions, and failure to maintain drainage systems. Sound familiar? If you’re worried about where your drainage fee goes, be thankful that you don’t live in Detroit. That city reports that 75% of the drains citywide are covered by debris or have a blockage.
V: Consequences of Urban Flooding
Talks about the economic and social costs of urban flooding. Did you know, for instance, that almost 40% of small business never reopen their doors following a flooding disaster? And that 90% of businesses fail within two years of being struck by a disaster? However, because no single federal agency collects and evaluates flood loss information, all national flood loss estimates are considered “approximations.” Therefore, the report says, they are of marginal use in conducting accurate economic analyses to support urban flood risk reduction mitigation.
Social costs hit moderate income, the old, and those facing social challenges the hardest. “For those lacking critical resources (savings, insurance, etc.), the flood losses gnaw away at their well-being.”
In regard to Houston, the study found that, “The urban flooding that occurs in the heart of the central city is mainly attributed to existing drainage infrastructure that predates today’s design standards or insufficient pipe sizes for the now fully developed urban areas.”
VI: What Can Be Done About Urban Flooding?
Examines different strategies to mitigate flooding:
Planning
Capturing rain where it falls
Eliminating or reducing risk
Adequate maintenance
Upgrading capacity standards
Risk communication (gaining better public understanding)
Better mapping
Disclosing risks in user-friendly ways
Insuring at-risk properties.
Some key insights:
Lack of funding and lack of political will are the most significant issues.
Much of the available funding requires a cost share and significant participation in the NFIP program. Most properties outside the mapped floodplain do not carry flood insurance. This then requires localities to fund these initiatives by themselves.
New development outside the floodplain generally has limited stormwater control requirements. Local CEOs are often reluctant to require stormwater controls as they fear this would dissuade development.
VII. Major Challenges
Includes discussions of lack of resources, population/urban growth, climate change, priority setting and fragmented governance.
If you want to understand why flood mitigation and what needs to be done to fix it, read this report.
VIII. Moving Ahead: Challenges and Recommendations
The study outlines ten challenges and makes 9 recommendations. Most target government leaders and policy makers. They are much too detailed to summarize here without tripling the length of the post. But if you want to know what you should push your representatives to consider, you must read section.
Number 8 read: “Governments, at all levels, have not provided effective means to communicate risks to those in urban flood- prone areas. A significant number of these areas are not identified by maps produced under the Federal Emergency Management Agency National Flood Insurance Programs, and actions by those responsible for urban flood mitigation are needed to delineate these areas. Communication of flood risk is often seen by public officials and developers as a negative.”
In my opinion, it’s a positive. A better understanding of risk could help everyone make better decisions that prevent heartbreaking losses, such as those we saw with Harvey.
All in all, this is a must read for anyone who wants to understand urban flooding and why it is so difficult to address.
Acknowledgements:
For University of Maryland
Dr. Gerald E Galloway
Dr. Allison Reilly
Sung Ryoo
Anjanette Riley
Maggie Haslam
For Texas A&M University
Dr. Sam Brody
Dr. Wesley Highfield
Dr. Joshua Gunn
Jayton Rainey
Sherry Parker
Posted by Bob Rehak on 12/2/2018 with thanks to Jacque Havelka
460 Days since Hurricane Harvey
https://i0.wp.com/reduceflooding.com/wp-content/uploads/2018/12/TAMU-Cover.jpg?fit=1500%2C1916&ssl=119161500adminadmin2018-12-01 20:16:182018-12-01 20:27:57Growing Threat of Urban Flooding Labeled National Challenge by New Study
Texas Water Conservation Association Issues Report on Pros and Cons of Flood Mitigation Strategies
The Great Lakes Dredge finally liberated the ditch that drains the western third of Kingwood 462 days after Harvey.
A new report by the Texas Water Conservation Association reviews the relative merits and problems with various flood mitigation strategies. The strategies include pre-release from reservoirs; on- and off-channel reservoirs; aquifer storage and recovery; and dredging. Anyone who wants to understand how professionals evaluate the merits of different strategies should read this concise, clearly written, 25-page report called Flooding in Texas: Preparation and Response.
About the Authors
The Texas Water Conservation Association is an association of water professionals and organizations in the state of Texas. Its members represent river authorities, municipalities, navigation and flood control districts, drainage and irrigation districts, utility districts, municipalities, groundwater conservation districts, all kinds of water users, and general/environmental water interests. Membership includes engineers, hydrogeologists, attorneys, government administrators, and numerous other individuals committed to Texas water resource management. Don’t be scared by the author’s titles.
Bias Toward Conservation over Mitigation
The only warning I have: the authors have an inherent bias toward water conservation as opposed to flood mitigation, as their name would imply. That said, it’s important for people who flooded to understand that flood control is not the main responsibility of people who operate dams. Water conservation is.
Three Types of Reservoirs
The report starts with a discussion of the three main types of reservoirs: water-supply, flood-control, and dual-purpose reservoirs. Lake Conroe and Lake Houston are both water-supply reservoirs. Texas has 150 such reservoirs, by far the most common type.
That section ends with this admonishment: “In water supply reservoirs, there is often very little storage available between maximum design impoundment and the top of the gates. This distance is sometimes referred to as freeboard and should not be considered extra storage, as it is unsafe to operate in that manner. A reservoir that attempts to indefinitely impound stormwater without an emergency spillway will eventually overtop at the lowest elevation across the dam, usually the top of the control gates. This kind of operation is dangerous as it jeopardizes the integrity of the dam, potentially resulting in a dam failure. For this reason, reservoir operators follow specific flood operation protocols to ensure that the dam is not breached.”
Four Main Mitigation Strategies Examined
A discussion of four main flood mitigation strategies follows.
Many people in the Houston area question why Lake Conroe did not release earlier during Harvey. Factors that influence whether prerelease may be of help or hurt include:
Direction of Approaching Storm is Crucial in Pre-Release
During Harvey, a factor that weighed heavily in the decision-making at the Lake Conroe Dam was the direction of the approaching storm. Because it approached from the Gulf, operators worried that pre-leasing water would overload downstream communities which already struggled with the local rainfall.
On the other hand, both the Memorial and Tax Day floods approached from the West or North. In those cases, pre-release was safer.
This section concludes with the observation that, “Harvey dumped approximately … 75 million acre feet of water. Texas’ statewide water conservation storage is approximately 31.5 million acre feet. … No amount of prerelease, and no amount of temporary or permanent conversion of water supply storage, would have appreciably reduced the magnitude of flooding caused by Hurricane Harvey.” And later, “Prerelease is a strategy with inherent risk, because the decision making regarding its use is based on imperfect predictions.”
On-Channel Reservoirs: A Proven Approach
Next, the report considers On-Channel reservoirs, such as Barker and Addicks. “On-channel reservoirs,” they say, “are an important component of the flood mitigation discussion, and have demonstrated effectiveness in multiple areas of the state. As an added benefit, on-channel reservoirs also provide an opportunity to double as a major water supply source, as many of the state’s dual-purpose reservoirs have done for decades.” Harris County Flood Control budgeted for these in its $2.5 million flood bond.
Off Channel Reservoirs Have Severe Limits
Off-Channel Reservoirs represent a less attractive alternative. Sand miners fondly point to the extra storage capacity in their pits for flood mitigation. However, the report points out that pumps can’t work fast enough to create meaningful reductions in flood levels. Other problems: very limited capacity, pumping costs, and debris floating in the water that could clog pumps.
Pros and Cons of Aquifer Storage and Recovery (ASR)
Many people have discussed the possibility of aquifer storage and recovery. It has proved to be a viable strategy for water supply. Managers pump excess water underground for storage in aquifers until needed for future use.
“Initial feasibility and pilot-testing studies are important,” say the authors, “as ASR requires the right physical conditions (e.g. geology, ground slope, groundwater quality) to be feasible. It also must be economically competitive with other viable options.”
“For ASR to have any meaningful impact in an extreme flooding event, extensive off-channel storage would be required, because the rate at which water could be injected underground is so slow in comparison to the rate of flood flows. As such, the off-channel storage is actually the mechanism for mitigating the flood in this case, not the ASR system.”
“As a flood control strategy, however, ASR cannot provide a first line of defense during an extreme storm event due to its need for extensive storage and treatment and its inability to compete economically with other solutions.”
Also, water treatment would be needed before pumping it into the ground because water quality in large flood events is extremely degraded.
When Dredging Helps
The report discusses many purposes for dredging and extensively references the Army Corps’ emergency project on the San Jacinto. It discusses dredging in rivers, streams, lakes, and ditches; for maintenance, navigation, and to remove blockages (like those we have); from cost, environmental, technical, and disposal points of view. Authors lament the expense of dredging but acknowledge its usefulness in certain cases.
Need for Single Source of Emergency Communication
Before closing, the reports also addresses the need for a consistent, focused communication protocol to warn people when flood gates will open. This section also discusses the regulatory environment that dam operators live within. In other words, the restraints that they face.
It concludes by saying that, “During a flood event, it is important that evacuation orders and flood warnings come from a single, designated source to avoid confusion and ensure accurate information for the public. In Texas, the leading notification providers are local Emergency Operations Centers (EOCs) and the National Weather Service (NWS). Reservoir conditions are one piece of the flooding puzzle and operators must provide real-time information to EOCs and the NWS so those entities can weigh all contributing factors to provide the best possible flooding information to the public.”
Look at Flooding from Professional’s Perspective
If you want to understand the world from a water-professional’s point of view, read this thought-provoking report. I didn’t agree with everything in it, but usually when I didn’t, it was because they were referencing another location, not ours. The author’s freely acknowledge that every watershed is unique and must be evaluated from its own perspective.
Posted on December 3, 2018 by Bob Rehak
462 Days since Hurricane Harvey
River Grove Boat Ramp May Open Next Week
Some unexpected good news! The River Grove boat ramp could soon open…as early as next week. The Great Lakes Dredge is starting to chew its way through the massive side bar that has had Kingwood’s only boat dock shut down for 16 months.
The original speculation was that the Army Corps would leave River Grove alone until the rest of the job was complete. Corps officials told me that they worried about the safety of recreational boaters around the massive dredging equipment and pipelines.
Something must have changed because at 8 a.m. this morning, Bruce Casto snapped this shot on his cell phone. Bruce heard second hand from another person in the park that someone on the dredge yelled across the water that, “The boat dock will be open in a week.”
I try not to repeat rumors but I’ve known Bruce for a long time and trust him. And given the location of the dredge in this photo, there is a better than 50/50 chance that River Grove will soon open. I have not verified that yet with the Army Corps of Engineers because of the timing of this surprise (on the weekend).
Posted on 12/3/18 by Bob Rehak
461 Days since Hurricane Harvey
Growing Threat of Urban Flooding Labeled National Challenge by New Study
Researchers at Texas A&M Galveston and the University of Maryland have just published a massive new study on The Growing Threat of Urban Flooding: A National Challenge. The study – a treasure trove of insights – actually started in 2016, before Harvey.
It focuses primarily on urban flooding as opposed to riverine flooding, which caused many of the Lake Houston Area’s problems. However, area residents should not dismiss it. The two types overlap and the report largely addresses issues that exacerbate both, such as inadequate governmental systems, engineered structures and growth that overwhelms both.
The report contains eight major sections that quantify the scope of the challenge. Below, a few highlights from each.
I. Urban Floods: The Nation’s Hidden Challenge
Documents the stunning extent of urban flooding and factors that continue to make it worse. Did you know for instance, that two thirds of the nation’s population living in floodplains live in just two states: Texas and New York? Or that Texas led the nation in billion-dollar water and wind disasters between 1980 and 2018?
II. Analyzing Urban Flooding
Reveals statistics on the scope of the problem. Two gems:
III. Where Urban Flooding Occurs
Shows that Texas ranks in the middle of the pack in terms of frequency of events, as opposed to major events. The researchers found that nationwide, approximately 25% of all flood insurance claims are submitted by policy holders whose property lies outside the 100-year flood plain. New York found that “The problem in most communities is lack of enforcement. Communities need a comprehensive plan to address development, infrastructure needs, stormwater runoff, and building codes. When a community doesn’t address these issues it only exacerbates other problems and continued urban sprawl eats up rural areas causing flooding, erosion, and infrastructure malfunction.”
IV. Why Does Urban Flooding Happen?
Examines aging and inadequate drainage systems, increases in local and regional runoff, sewage and stormwater backups, changes in local physical conditions, and failure to maintain drainage systems. Sound familiar? If you’re worried about where your drainage fee goes, be thankful that you don’t live in Detroit. That city reports that 75% of the drains citywide are covered by debris or have a blockage.
V: Consequences of Urban Flooding
Talks about the economic and social costs of urban flooding. Did you know, for instance, that almost 40% of small business never reopen their doors following a flooding disaster? And that 90% of businesses fail within two years of being struck by a disaster? However, because no single federal agency collects and evaluates flood loss information, all national flood loss estimates are considered “approximations.” Therefore, the report says, they are of marginal use in conducting accurate economic analyses to support urban flood risk reduction mitigation.
Social costs hit moderate income, the old, and those facing social challenges the hardest. “For those lacking critical resources (savings, insurance, etc.), the flood losses gnaw away at their well-being.”
In regard to Houston, the study found that, “The urban flooding that occurs in the heart of the central city is mainly attributed to existing drainage infrastructure that predates today’s design standards or insufficient pipe sizes for the now fully developed urban areas.”
VI: What Can Be Done About Urban Flooding?
Examines different strategies to mitigate flooding:
Some key insights:
VII. Major Challenges
Includes discussions of lack of resources, population/urban growth, climate change, priority setting and fragmented governance.
If you want to understand why flood mitigation and what needs to be done to fix it, read this report.
VIII. Moving Ahead: Challenges and Recommendations
The study outlines ten challenges and makes 9 recommendations. Most target government leaders and policy makers. They are much too detailed to summarize here without tripling the length of the post. But if you want to know what you should push your representatives to consider, you must read section.
Number 8 read: “Governments, at all levels, have not provided effective means to communicate risks to those in urban flood- prone areas. A significant number of these areas are not identified by maps produced under the Federal Emergency Management Agency National Flood Insurance Programs, and actions by those responsible for urban flood mitigation are needed to delineate these areas. Communication of flood risk is often seen by public officials and developers as a negative.”
In my opinion, it’s a positive. A better understanding of risk could help everyone make better decisions that prevent heartbreaking losses, such as those we saw with Harvey.
All in all, this is a must read for anyone who wants to understand urban flooding and why it is so difficult to address.
Acknowledgements:
For University of Maryland
For Texas A&M University