Maintaining the path to safety27 April 2021
Effective and regular maintenance practices are an important component of good dam safety programmes. Any existing structural deficiencies or delays will create additional vulnerabilities as extreme weather events become more commonplace with climate change. Report by Suzanne Pritchard.
Recent concerns about the condition of a small dam in the US have highlighted the ongoing issue over maintaining ageing dams, particularly where there are questions over ownership and responsibility.
New Rochelle Reservoir No 1 Dam is located on the Hutchinson River in the town of Eastchester and the city of New Rochelle in Westchester County, New York. It was originally constructed around 1894 by the New Rochelle Water Company and used for water supply. Consisting of a masonry section about 206m long with earth embankments on each end, its primary spillway is an overflow channel approximately 9m wide near the middle of the masonry section. Dam height varies from 9m in the centre to about 1.8m at the end. Due to the presence of the Hutchinson River Parkway immediately downstream, it is classified as a Class C High Hazard dam.
The reservoir is no longer used by the water company and is primarily used for recreational purposes. According to New York State Department of Environmental Conservation (NYSDEC) records, the dam is presently owned by:
- City of New Rochelle (left embankment section and left masonry section from the centre of the spillway to left abutment).
- Block 138 Corporation (right masonry section from the centre of the spillway to the right abutment).
- Town houses at Lake Isle Association (right embankment section).
Maintenance of the dam has been lacking for many years. In August 2018, after visual safety inspections were conducted, NYSDEC assigned the dam a condition of Unsound, Deficiency Recognised. While earlier in March 2018, the New York Department of Conservation is reported to have filed legal action to compel the dam owners to repair the structure: a situation compounded by the fact that Delaware company Block 138 Corporation is reported to have dissolved over 30 years ago, leaving unanswered questions over who has responsibility for its part of the dam.
Hutchinson River Parkway in Eastchester, New York. Due to its presence immediately downstream, New Rochelle Reservoir No 1 Dam is classified as a Class C High Hazard structure.
In 2020 Mott MacDonald prepared dam inspection and assessment reports on behalf of the City of New Rochelle. The company said that based upon a review of information and inspections, it agrees with the current rating of “Unsound, Deficiency Recognised” and stated that the dam does not meet all safety criteria.
Mott Macdonald listed a host of maintenance deficiencies in its Dam Assessment Report of August 2020. Significant trees and woody vegetation were observed on the downstream slope of the dam embankment at the masonry section, and along the upstream slope of the right earthen dike. It is recommended that a development plan is implemented for their removal and should include:
- Removal of large stumps and roots.
- Clearing the vines and root intrusion on the masonry dam.
- Restoring/replenishing of riprap slope protection as needed.
- Filling in eroded areas and depressions.
- Re-establishing grass vegetation.
- Repairing several of the mortar joints along the masonry dam due to erosion and root intrusion.
In addition, minor seepage or wet spots were also observed along the stone masonry dam, and Mott MacDonald recommended that the damaged or missing joints should be repaired to help reduce the potential for seepage. Any observed seepage or wet spots should continue to be monitored for changes in the current conditions.
The dam assessment added that consideration should also be given to removing or relocating the security fencing along the crest of the masonry section of the dam which could be a safety concern to the structural integrity of the dam during an overtopping event.
Some undermining of the spillway wing walls was also observed along the spillway chute/discharge channel, while the downstream end of the spillway discharge channel is cracking and collapsing into the plunge pool. Erosion of the downstream channel was observed at the plunge pool and is probably due to the collapsing discharge channel. The above damage appears to have been present since the US Army Corps of Engineers carried out an inspection in 1979.
Furthermore, Mott MacDonald’s hydrologic and hydraulic analysis concluded that the existing dam “does not have the spillway capacity to safely convey the SDF (50% of the PMF storm event)”. Action required to bring the dam into compliance with the requirements of dam safety include:
- Spillway Modifications – At a cost of about US$4million, the dam would need to be modified to increase spillway capacity which includes lowering the primary spillway by approximately 1.2m and converting the left masonry dam into a secondary or auxiliary spillway.
- Overtopping Protection - The dam would require modifications to the downstream slopes to ensure integrity and stability during an overtopping event and could cost in the range of US$8 million.
- Dam Removal –Permanent breaching to eliminate the dam and the reservoir would cost about US$3million. Dam removal will have potential downstream impacts.
Based on the deficiencies noted at the dam and due to the lack of maintenance that continues, NYSDEC recommended that the impounded water level be lowered until “responsible ownership is in place” and any remedial measures have been performed.
In a recent paper published by Peter K Brewitt and Chelsea Colwyn in WIREs Water, the authors discuss the legal and policy issues of non-jurisdictional dams in the US, and say that the onus should fall on private dam owners to ensure their structures are properly inspected and maintained.
According to Brewitt and Colwyn, most of the US’ 2.5 million dams are not under the authority of any public agency. These small dams are under 1.83m tall and described as being unregulated, not inventoried anywhere, endangering public safety and deteriorating riparian ecosystems. The authors say that as the majority of American dams are more than 50 years old and suffer from a nationwide multi-billion-dollar backlog in maintenance, problems are only increasing due to the impact of climate change.
However, they believe that several policy changes and legal actions will help states to “vastly improve the situation”. Passing owner-responsible legislation and educating owners about their rights and responsibilities would be a positive step forward.
“The onus should fall on private dam owners to ensure that their structures are properly inspected and maintained,” the authors say. “Many landowners have little knowledge about their dams and the policies governing them; some may not even know that their land contains old dams. States should educate owners about their legal responsibilities and liabilities, and owners’ liability should be reduced when they comply with dam safety legislation.”
The authors go onto add that state jurisdiction of dam safety agencies should be expanded to embrace dams of any size, while all small dams need to be identified and inventoried. For those dams that are considered “defunct” and where “dam owners would probably be glad to be free of responsibility”, the dam removal process should be streamlined by relevant agencies, and creative funding mechanisms should be explored. In addition, states should encourage industrial land users to pay for dam removal to mitigate the impacts of development.
Costly deferred maintenance
As civil engineer Antti Ruokonen explained in the Law Fare Blog, deferred maintenance of critical infrastructure is a local, state and federal challenge that is a global phenomenon. A 2019 report by the nonpartisan think-tank Volcker Alliance, estimates that deferred maintenance in the US could already exceed an estimated US$1 trillion, or five percent of the country’s gross domestic product.
“In infrastructure, utilities, buildings and other systems, deferred maintenance consists of structural repairs and necessary upgrades that are postponed—usually for budgetary reasons—until the next year,” Ruokonen said. “The monetary costs associated with deferred maintenance continue to grow until maintenance is done. In some cases, the cost of deferral reaches a point where the level of funding required is identical to that required to build a completely new structure.”
Referring to the US state of Alabama which is the only one in the country without a safety programme for its dams (which number in excess of 2200), Ruokonen said that “Alabama’s extreme negligence in dam maintenance is a stunning example of dangerously unregulated and crippling infrastructure.”
Ruokonen also spoke about the cumulative effect of deferred maintenance and climate change and how it is considered a threat to national security.
“Extreme weather phenomena are already increasing in frequency and intensity,” he said. “The recent destructive hurricanes and wildfires, such as those in California, are just the tip of the spear. As these effects continue to multiply, all infrastructure will be subjected to more pressure. Existing structural deficiencies will create additional vulnerabilities and a possible cascade effect that could endanger multiple sectors of society and security infrastructure simultaneously.”
Legislative path to safety
Building upon previous legislation to help improve the condition and safety of the US’ ageing dam and levee infrastructure, Congress passed the Water Resources Development Act of 2020 (WRDA 2020) in late December. This new bipartisan water infrastructure legislation is setting a path towards safer dams in the US, the Association of State Dam Safety Officials (ASDSO) believes.
Included within WRDA 2020 are improvements to the National High Hazard Potential Dam Rehabilitation Act. These include clarifying who the recipients and sub-recipients for this grant programme can be, and the procedures, roles and responsibilities for plans and maintenance requirements. The new provisions allow small hydropower producing dams to be eligible for the grant.
The full WRDA 2020 bill addresses additional water infrastructure needs such as improvements to the USACE Levee Safety Programme, increasing water storage, providing protection from dangerous floodwaters, deepening nationally significant ports, maintaining the navigability of inland waterways, and addressing the threat of invasive species across the country. ASDSO says that the legislation also cuts red tape, is fiscally responsible, and strengthens national security.
Toddbrook reservoir in England fills to capacity due to heavy rain on 31 July 2019. The following day the spillway failed and led to the evacuation of hundreds of local people. Intermittent maintenance over the years was reported as being a contributory factor to the failure.
Over in the UK, the Canal and River Trust is feeling the growing pressure of climate change and the continued maintenance of its historic canals and river navigation network. The trust is a charity that looks after one of the oldest critical infrastructure networks in the world where more than 3200km of waterways extend across the country.
Most of the vital earth structures supporting these man-made waterways were built when civil engineering and geology were in their infancy and there were no standards or previous experience to draw on. The trust says its canal network was built for the demands of the late 18th or early 19th centuries with little expectation that its asset life would stretch over 200 years.
Increasing extremes in weather patterns are bringing considerable challenges to this ageing infrastructure and will require an unprecedented scale of expenditure to maintain its resilience and, ultimately, protect public safety.
However, the Canal and River Trust cautions that this not a distant future scenario; we are already experiencing regular extreme weather events on an unprecedented scale. The damage that incurred at its Toddbrook Reservoir in 2019 followed the rare combination of two consecutive storm events. In early 2020, storms Ciara, Dennis and Jorge – three major events within a month or so – collectively caused millions of pounds of damage across the waterways network in the north of England. Then in August 2020, following intense local rainfall and severe flooding in Scotland, the embankment carrying the Union Canal was breached. Furthermore, long dry weather spells can also be a serious problem causing earth structures to dry out and increase their vulnerability to erosion, especially if followed by intense rainfall when the weather breaks.
“We believe that there needs to be a step change in the scale of expenditure on high risk infrastructure – such as reservoirs, culverts, embankments, and cuttings – over the next five years or so, if we are to keep pace with the growing incidence of extreme weather and ensure that these highly-valued waterways remain available for people to enjoy and safe for the communities they run through,” the Canal and River Trust said.
Undertaking the vital work to increase the resiliency of the waterways over the next few years will require an additional investment of more than £200million.
In December 2020, the trust announced a £5 million upgrade to Harthill Reservoir in South Yorkshire, England. The reservoir, situated between Sheffield and Worksop near to the village of Harthill, was constructed more than 200 years ago to supply water to the Chesterfield Canal.
Over the next few months, a range of ground investigation and topographical studies will be carried out, along with heritage and ecological assessments. The main project is expected to start in 2022 and be completed within 12 months. Reservoir water levels will be temporarily reduced until the upgrade work is completed.
Sean McGinley, Yorkshire and North East regional director of the Canal and River Trust, said: “From time to time we need to upgrade and improve the canal infrastructure to present day standards. This project will involve redesigning the overflow spillway to increase the resilience of Harthill Reservoir. This important upgrade work will secure Harthill Reservoir’s long-term future and ensure that people can continue to enjoy the important physical health and wellbeing benefits of being by water for many years to come.”
Earlier in October 2020, the trust also announced that its £3 million major restoration programme at the Tees Barrage had reached the halfway milestone.
This project is the most extensive to be undertaken to date. All four gates and cylinders are being refurbished for the first time since it opened. A 150-tonne crane and team of engineers worked to refurbish the second of the four original 12m long cylinders which are used to operate the 88-tonne belly gates of the barrage. The cylinders should have another 25-year lifespan.
The barrage which straddles the River Tees at Stockton in the north east of England, cost £55 million to build in 1995 and stands 70m wide. Construction included a lock for boat navigation, fish passes for migratory fish as well as tidal power generation.
The River Tees Barrage in England under maintenance in July 2020.
Dam Safety Inspection Report. New Rochelle Reservoir No. 1 Dam. YYSDEC IDC No 215-0207. January 6, 2020. Mott MacDonald.
Dam Assessment Report. New Rochelle Reservoir No. 1 Dam. DEC Dam ID # 215-0207 August 10, 2020. Mott MacDonald.
Little dams, big problems: the legal and policy issues of non jurisdictional dam. Peter K Brewitt and Chelsea LM Colwyn. WIREs Water. Volume 7, issue 1. https://doi.org/10.1002/wat2.1393.
National Security Implications of Deferred Maintenance in Infrastructure By Antti Ruokonen. 8 January 2021. https://www.lawfareblog.com/national-security-implications-deferred-maintenance-infrastructure
Bipartisan Water Infrastructure Legislation Sets Path Toward Safer Dams. ASDSO. Posted January 5th, 2021 by K. Riley. https://www.damsafety.org/article/legislative/bipartisan-water-infrastructure-legislation-sets-path-toward-safer-dams