Natural Security: Charles River, Massachusetts
Wetlands as Flood Protection
Challenge
The Charles River watershed is the most densely populated river basin in New England. Urban and suburban development from Boston, Cambridge and surrounding communities has paved over much of the lower river’s wetlands and natural landscapes, reducing natural water storage and causing downstream flooding. Major floods hit the basin in 1938, 1955 and 1968, causing millions of dollars in damages. The Army Corps of Engineers began examining how the repeated disasters could be avoided in 1965. They found that wetlands played a major role in storing excess floodwaters and reducing damage on the upper and middle portions of the Charles River. Yet even as their value became clear, wetlands continued to disappear due to development. Wetlands in Massachusetts were disappearing at a rate of 1 percent per year, with the greatest pressure on the Charles River wetlands. Destroying upper basin wetlands would not only extend flooding problems throughout the watershed, it would also worsen the lower basin’s predicament, as floodwaters would move downstream more quickly. If local leaders were to solve the lower basin’s recurring flooding and prevent those problems from spreading upstream, they would need to preserve existing wetlands and relieve the pressure from accelerating development.
Approach
In 1972, the Corps began work to alleviate flooding in the lower basin by replacing the existing dam at the mouth of the river. The new dam was completed in 1978 with a large pumping station to discharge 630,000 gallons of water per minute into Boston Harbor when the river gets too high. The Corps of Engineers’ initial proposal for the basin also called for levees and a second dam along the middle portion of the Charles River at an estimated cost of $100 million ($618 million in today’s dollars). However, when the 1968 flood hit, the Corps witnessed the capacity of the wetlands to store flood waters and decided to preserve them. In 1977 the Corps began purchasing land and acquiring easements, prioritizing parcels by location, storage capacity and threat of development. By 1983, the Corps had purchased 3,211 acres and acquired easements on 4,882 acres of private land. The protected area includes 75 percent of all existing wetlands in the Charles River watershed.
Benefits
Protection of the Charles River wetlands has provided numerous benefits to communities throughout the basin. Without protection, the Corps estimated that 40 percent of all existing wetlands at the time would have been lost to development by 1990. The wetlands have protected downstream communities on numerous occasions in recent decades. They prevent an estimated $40 million in flood damages every year. In contrast, communities in neighboring basins without in tact wetland systems have continued to suffer flood damages. In May of 2006, the community of Lawrence, which lies at the confluence of the Merrimack, Shawsheen and Spicket rivers, received 8.73 inches of rain over several days, resulting in an estimated $19 million in flood damages. At the same time, communities along the Charles River, including Boston and Cambridge, received 8.99 inches – the second highest four-day total in 134 years of record-keeping - and suffered almost no flood damage.
The protected wetlands provide a wide range of other water quality, recreational and economic benefits as well. There are 212,000 visitors to the protected area every year, and they contribute over $4.5 million to the local economy. Properties adjacent to the protected wetlands have shown direct benefits to local residents through increased property values. In all, the Charles River wetland protection project has been a great benefit to the watershed. In contrast to a flood control dam which would have cost over $100 million and provided few, if any, additional benefits, wetland purchases and easements cost less than $10 million and contribute over $95 million to the regional economy every year.
Adapting to a Changing Climate
The preservation of wetlands within the upper Charles River basin will be even more essential in a warming world. The number of heavy precipitation events in the northeast is projected to increase 8 percent by 2050 and 12-13 percent by the end of the century. As extreme storms become more frequent, the protected wetlands will continue to absorb floodwaters and release them gradually over the course of weeks or months, avoiding the deadly peak flows that can take lives and destroy communities. On the other hand, paving over these wetlands to support development would allow floodwaters to pick up speed and move rapidly downstream, amplifying the impact of more frequent and intense storms to come. The protection of the wetlands has also prevented new development in flood-prone areas, which will reduce the number of vulnerable structures as weather events become more extreme. In combination with the flood control dam in the lower basin, communities along the Charles are well equipped to withstand large floods without suffering devastating losses. The same is not true of neighboring watersheds that are stripped of their wetlands, and this vulnerability will be magnified as the climate shifts.
