Since 2007, NSRWA has worked with the Town of Scituate to balance municipal water demand with ecological streamflow requirements. The goal is to restore more natural seasonal flows and providing adequate flow for fish migration in the First Herring Brook, a tributary to the North River. As we see in so many other areas in our watersheds, water withdrawals, dams, and development have impacted natural streamflows, limiting the First Herring Brook’s ability to support native river species, including migratory river herring. Scituate’s doubling of water use in the summer months and failing infrastructure issues create additional stressors to the water system and factors to consider in its management.
One of the ways that the NSRWA and MassBays help Scituate comply with its State Water Management Act permit is to provide summertime forecasting of reservoir levels to aid the town in decision making around outdoor watering bans and streamflow releases. The model uses a number of inputs – including current reservoir level and water demand provided weekly from the Water Department – and forecasts reservoir levels using the lowest 20th percentile of precipitation (a very conservative forecast for precipitation) and the highest water useage for that period during the past 5 years. This allows the town to review when the reservoir will reach levels that trigger demand management actions, including water bans and curtailing streamflow releases using very conservative assumptions.
These demand management trigger levels are part of the First Herring Brook Interim Operational Plan that were approved by the Water Commissioners (who are also the Select Board members) in 2018. This plan sets out a policy for the Water Department to initiate an outdoor water ban when the reservoir reaches 49% full. When the reservoir drops lower, down to 20% full, streamflow that had been released to support habitat downstream is then curtailed. Over the last few years, residents of Scituate have experienced outdoor watering bans during times of infrastructure failure in order to protect the system.
MANAGING STREAMFLOWS
There are two methods that the town of Scituate uses for managing streamflow. The first is releasing water from the upper reservoir into Old Oaken Bucket for water supply and to maintain flows downstream.
The Water Department also uses a series of notched boards in the fish ladder to manage streamflow out of Old Oaken Bucket Pond. During the spring, when fish migrate from the ocean to their spawning grounds upstream, we need to be sure flows are as high as possible to allow for their passage. The picture below left is the correct way for the fish ladder to be operating from April 1 – May 31 to allow for immigrating adults. The top board of the fish ladder must be removed for flows to be appropriate and the town should release enough water from the reservoir to meet demands and allow for streamflows. In the fall, juvenile fish that are leaving the system need enough flow to travel to the ocean. In order to meet these goals, the town installs a notched board at the top of the fish ladder. The notched boards allow a smaller amount of water to trickle out of Old Oaken Bucket to conserve water for summertime demands while allowing smaller juvenile river herring to make their way back to the ocean.
The ultimate goal is for residents to conserve as much water as possible during the drier months before impacting the health of the ecosystem downstream. We need water to sustain us and for the natural world around us, but irrigating our lawns does not fall into either category. When Scituate has implemented and enforced outdoor watering restrictions in the past, usage has decreased by as much as 25%! That’s enough water to run the fish ladders and allow for streamflows in summertime.
As a result of the infrastructure issues that Scituate’s Water Department has to manage and the droughts we all have experienced in the last few years, the town has a number of factors to consider in its approach to streamflow management. Alternating droughts and rainy summers have shown that using the NSRWA adaptive model can be useful for predicting when water demand management actions are needed to preserve the public drinking water supply and the ecological resources in the First Herring Brook. For more information on this partnership, visit the First Herring Brook Restoration page.
