A series of catastrophic dam failures in the 1920s prompted critical safety reforms and engineering advancements that significantly improved the security of reservoirs. These historical disasters, born from flawed construction and insufficient oversight, led to new legislation and a century of relative stability in dam safety. Now, however, a new and unpredictable variable is testing the limits of this aging infrastructure. The escalating climate crisis, bringing with it extreme rainfall and weather volatility, is placing unprecedented strain on dams designed for a climate that no longer exists, forcing a modern reassessment of reservoir safety.
Nearly a century of successful containment has been built upon the lessons learned from these early 20th-century tragedies. The deadly dam collapses at Dolgarrog in Wales and Skelmorlie in Scotland during 1925 exposed critical weaknesses in design and maintenance, shocking the public and lawmakers alike. These events directly spurred the passage of the Reservoirs (Safety Provisions) Act of 1930 in the UK, a landmark piece of legislation that established rigorous, legally mandated standards for the design, construction, and regular inspection of large reservoirs by qualified engineers. This act became the foundation of modern reservoir safety management, shifting the industry from a reactive posture to one of proactive oversight and ushering in an era of improved reliability.
Historical Failures as a Catalyst for Change
The 1920s were a turning point for reservoir safety, largely due to two devastating failures that highlighted the dangers of unchecked construction. In April 1925, a reservoir failure at Skelmorlie, Scotland, set a worrying precedent. This was followed in October of the same year by the infamous Dolgarrog disaster in north Wales. After a month of heavy rain, two dams holding back the Eigiau and Coedty reservoirs failed. The breach at Coedty was particularly catastrophic, unleashing approximately 1.7 million cubic meters of water in a torrent that swept through Dolgarrog village. The flood destroyed homes, a bridge, and a chapel, killing 16 people, including six children, because there was no time to issue a warning.
These events captured national attention, revealing a pattern of inadequate construction methods and a severe lack of maintenance protocols. The public outcry and subsequent investigations led directly to the formulation of the 1930 Reservoirs Act, the first comprehensive attempt in the United Kingdom to regulate reservoir safety through law. It mandated that large reservoirs undergo periodic inspections by certified engineers, ensuring that potential issues were identified and addressed before they could escalate into disasters. For decades, this legislation has been credited with the UK’s strong safety record, preventing a repeat of the 1920s tragedies.
New Risks from a Changing Climate
The safety standards born from the 1930 Act were designed based on the climatic conditions and engineering knowledge of that era. Today, however, climate change is introducing weather patterns far more extreme than what these older structures were built to withstand. Professor Jeff Warburton of Durham University warns that more frequent and intense weather events are putting these aging reservoirs under serious new strain. The primary threat comes from extreme rainfall, which can overwhelm a dam’s spillway—the structure designed to release excess water safely. When a spillway’s capacity is exceeded, water flows over the top of the dam itself, an event known as overtopping, which is the leading cause of dam failure.
This increased risk is not limited to periods of intense rain. The volatility of the modern climate also includes prolonged droughts, which introduce a different set of challenges. Rapid and sustained decreases in water levels can affect the structural integrity of dams, particularly older embankment and masonry designs. These structures are often more susceptible to internal erosion, seepage through cracks or foundations, and slope instability. The combination of more intense storms and deeper droughts creates a cycle of stress that can accelerate the degradation of materials and compromise the fundamental stability of a reservoir, raising fears that the safety margins of the past may no longer be sufficient.
The 2019 Toddbrook Dam Incident
A Modern Near-Disaster
The vulnerability of aging dams to modern weather extremes was starkly illustrated in the summer of 2019 at the Toddbrook Reservoir in Derbyshire, England. Following a period of intense rainfall where the area received a month’s worth of precipitation in just two days, the dam’s emergency spillway was overwhelmed by the sheer volume of inflow. Water began cascading over the spillway, causing a large section of its concrete face to collapse and exposing the dam’s earthen core. This damage raised immediate fears of a total breach, which would have sent a catastrophic flood into the downstream town of Whaley Bridge.
An Unprecedented Emergency Response
The potential for disaster prompted a massive emergency intervention. Authorities ordered the immediate evacuation of more than 1,500 residents from Whaley Bridge. To relieve pressure on the damaged structure, fire services deployed high-capacity pumps to lower the reservoir’s water level. In a dramatic race against time, a Royal Air Force Chinook helicopter was called in to drop 400 tonnes of aggregate onto the damaged spillway section to stabilize it and prevent further erosion. After several days of intensive work, engineers declared the dam stable, and the evacuation order was lifted. The Toddbrook incident served as a powerful wake-up call, demonstrating how quickly a severe weather event could push a major reservoir to the brink of failure and endanger nearby communities.
Reassessing Reservoir Safety for the Future
The near-miss at Toddbrook has refocused attention on the thousands of aging dams across the UK and other countries that were built to last-century standards. According to experts like Professor Warburton, the incident underscores the urgent need to re-evaluate and update safety protocols in light of the climate crisis. The engineering assumptions that were valid in the 1930s must be revisited to account for the increased frequency of extreme floods and droughts. This involves not only reinforcing physical infrastructure but also enhancing monitoring systems and emergency action plans.
Many older dams, particularly embankment and masonry types, remain especially vulnerable. Investment in upgrading spillways, reinforcing dam cores, and improving drainage systems is critical to ensuring these structures can handle the volatile weather of the 21st century. As the climate continues to change, proactive and sustained investment in this foundational infrastructure is essential to prevent the hard-won lessons of the 1920s from being tragically learned all over again.
