Natural Flow Regime and Ecological Integrity

In July 2013, the United States Geological Survey[1] (USGS) released CircularEcological Health in the Nation’s Streams, 1993—2005 1391 titled, “The Quality of our Nation’s Waters – Ecological Health in the Nation’s Streams, 1993-2005”.  Circular 1391 reported the approach and findings of multiple community assessments conducted in streams throughout the US.  Based on its application of integrated biological assessment (i.e., combined analysis of algae, macroinvertebrate, and fish communities), USGS concluded that at least one among these three biological communities was altered[2] in 83% of the assessed streams; while all three biological communities were altered in 22% of the streams considered.  The biological impairment USGS catalogued range from 79% in agricultural settings to 89% in urban settings.  A biological community was deemed unaltered in just 17% of the assessed streams.

By coincidence, in July 2013 Princeton Hydro, LLC completed, “The Monponsett Pond and Silver Lake Water Use Operations and Improvement Report”.  Princeton Hydro’s report, prepared on behalf of the Town of Halifax in Plymouth County, Massachusetts; was funded by a competitive grant program – the Massachusetts Sustainable Water Management Initiative (SWMI).  The overall principle of SWMI is stated as:SWMI Report cover

The Commonwealth’s water resources are public resources that require sustainable management practices for the well-being and safety of our citizens, protection of the natural environment, and for economic growth.

The central issue for us to consider was an archaic water management circumstance, established through an 1899 State legislative Act and further complicated by two crisis management episodes in the 1960s and 1980s, respectively; that authorized the City of Brockton, MA to source the majority of its municipal water supplies from three water bodies (Silver Lake, Monponsett Pond, and Furnace Pond) located near Halifax, MA.  Brockton is situated 20 miles northwest of its Silver Lake Water Treatment Plant (WTP).  Moreover, Silver Lake, Monponsett Pond, and Furnace Pond each lie in the headwaters of different watersheds.

Princeton Hydro’s Role: Review and Analysis of the Brockton Water Supply System

In December 2012, Princeton Hydro was asked by the Monponsett Watershed Association (MWA) and the Jones River Watershed Association (JRWA) to act as technical lead for a bid by the Town of Halifax seeking SWMI grant funding.  MPWA and JRWA viewed Princeton Hydro as an ideal partner for this project owing to our diverse skills and expertise in water resource management.  Moreover, although we work in a variety of settings throughout Massachusetts, as a geographic outsider, Princeton Hydro brought fresh perspective to a complex and controversial problem that has plagued southeastern Massachusetts for decades.  In late March 2013, our team was notified that our application would receive funding – our contract required that we complete all of our activities by June 2013 and issue our final report by mid-July.

Princeton Hydro examined an abundance of information regarding the macro-scale characteristics associated with Brockton’s water supply system.  Our review and analyses emphasized hydrologic and nutrient pollutant modeling of the individual water bodies that make up Brockton’s primary water sources.  Our objective was to evaluate the water supply system in the context of the overall natural resource regulatory framework as well as the impacts that current water management practices exert on the ecosystem, including the numerous ecosystem services that humans rely upon.Water Budget Chart

Overall, our evaluation of Brockton’s water sources demonstrated that existing water management practices are not sustainable – we showed that in an average year, Brockton uses the equivalent of every water drop that enters the Silver Lake watershed as precipitation.

Furthermore, Princeton Hydro demonstrated that the artificial movement of water across natural watersheds results in a suite of negative consequences for ecological and human communities that inhabit the setting.  The primary negative impacts of water management practice include deviation from natural stream flow regime in three watersheds: Jones River (Jones River watershed), Stump Brook (Taunton River watershed), and Herring Brook (North River watershed); accelerated cultural eutrophication of Monponsett Pond and Silver Lake; and, heightened concern for the long-term integrity of sensitive environmental settings such as the Stump Brook Wildlife Sanctuary and the Burrage Pond Wildlife Management Area.

Clean Flowing Water Defines Healthy Streams

As reported by USGS in Circular 1391, reduced stream health most frequently relates directly to manmade modifications of the physical and chemical properties of streams.  Maintenance of stream health in the face of land development requires that the physical and chemical properties of streams remain within the bounds of natural variation.  Land and water management practices lie at the heart of reduced aquatic ecological integrity.  The most common factors for reduced stream health include:

  • Stream Flow Fluctuation
  • Nutrient Enrichment
  • Changes in Temperature Regime
  • Changes in Light Availability
  • Contaminants
  • Exotic Taxa

Despite some of the bleak statistics reported by USGS about stream health in the US, Circular 1391 provides insight that can guide land and water managers toward better overall stewardship and even remediation of ecologically-damaged waters.  Moreover, although a distinct majority of streams exhibit altered biology, even in urban settings, USGS showed that more than 10% of assessed streams were not biologically altered and that statistic points to a silver lining; meaning that unaltered aquatic communities can be compatible with urban settings.

Possible Management Options for Brockton

The Brockton water system amounts to an unsustainable use of sources for water consumed well beyond the source setting.  The strain on waters in the source areas leads to cascading impacts on water quality, ecosystem functions, and property value – impacts that are consistent with diminished ecological integrity reported by USGS in Circular 1391.

As USGS demonstrated, there is widespread evidence that stream flow and nutrient status are the most critical variables for stream health, and by extension – aquatic health in general.  USGS also suggested that management strategies aimed at restoring aquatic health are best developed and applied at the local/ watershed scale, where there is an understanding of how land- and water-management activities modify the physical, chemical, and biological attributes of streams.

Princeton Hydro recommended that the most obvious alternative to existing water management practice is to apportion the Brockton water supply to more and/or different sources in order to alleviate strain on Silver Lake, Monponsett Pond, Furnace Pond and their respective individual watersheds – Brockton’s consolidation of three headwaters watersheds in order to export water to a distant region contradicts the basic tenets of modern watershed science.

Since 2008, a desalination plant (Aquaria located in Dighton, MA) has offered a seemingly sensible alternative source for Brockton to eventually offset as much as 50% of the approximately 9 million gallons of water currently sourced from Silver Lake daily, yet the City (despite a 20-year contract that requires multi-million dollar payments to Aquaria annually) declines to accept Aquaria’s desalinated water as an offset to its Silver Lake source.

Among conceptual alternatives for supply, we also suggested directly feeding stock water from Monponsett Pond (and/or Furnace Pond) into the Silver Lake WTP in lieu of diverting and diluting millions of gallons of nutrient-enriched water per year into the comparatively clean waters of Silver Lake.

Princeton Hydro also suggested that horizontal alignment of extraction wells placed into the highly transmissive Plymouth – Carver – Kingston – Duxbury (PCKD) aquifer system would represent a less ecologically-damaging water source that also could provide feedstock to the Silver Lake WTP.

Princeton Hydro readily acknowledges that development/utilization of any water source alternatives to the current Silver Lake system will require new capital investment or other additional costs by Brockton, but the long-term cost of unsustainable water supply management by Brockton is a costly endeavor right now.  And in the case of Brockton’s water supply system, Brockton and its customers are not bearing all of the current costs of its water management practice.

Even in a water-rich region like southeastern Massachusetts, deep conflicts over water management practices can and sometimes do erupt.  The magnitude of long-term water withdrawal that exceeds sustainability depends on the hydrologic effects that society is willing to tolerate, including the actual cost of infrastructure, labor, energy, and related items necessary to obtain, treat, distribute, and otherwise manage land and water resources responsibly.

Decision-makers today and in the future face increasing strains on natural as well as economic resources and particularly for water resource stewardship, sustainable management is becoming less an idealized notion and more an imperative.

[1] Carlisle, D.M., Meador, M.R., Short, T.M., Tate, C.M., Gurtz, M.E., Bryant, W.L., Falcone, J.A., and Woodside, M.D., 2013, The quality of our Nation’s waters—Ecological health in the Nation’s streams, 1993–2005: U.S. Geological Survey Circular 1391, 120 p.,

[2] USGS defined altered as the numbers and types of organisms were substantially different when compared to a regional reference stream.

Habitat Fragmentation – Culvert Blockages and Solutions


Culvert that is “perched” due to scour by high velocity flows through the pipe. ©Princeton Hydro.

The Bucks County Chapter of Trout Unlimited (Pennsylvania) and the Cooks Creek Watershed Association were featured in the Summer 2013 edition of Trout magazine, TU’s national publication, for their culvert inventory work in the Cooks Creek watershed.  Princeton Hydro was glad to assist via directly investigating and training of volunteers to inspect and document potential culverts in need of retrofit.  Princeton Hydro also completed design concepts and opinion of costs for two example culverts.  Identified culverts in need of retrofit will help the creek’s wild brown and brook trout.  Princeton Hydro based the training on the Vermont guidelines for rating culverts for pass-ability.  In this small watershed a total of 97 culverts were identified with 32 of them as potential barriers, and 11 identified as “high priority” in need of retrofit.

Why worry about culverts, you say?

One of the most unforeseen danger to the biodiversity in our river networks is habitat fragmentation through un-passable culverts throughout the United States.  While blockages via dams number upward of 100,000 or so, the blockages created by ecologically and biologically inefficient culverts is likely to number in the millions.   The majority of these culverts are located in headwater areas of rivers, which entail greater than 50% of most river miles in a watershed; a large cumulative impact.  As a result, native key headwater species such as brook trout (Salvelinus fontinalis) in the East and cutthroat trout (Oncorhynchus clarkii) in the West have had their historic ranges reduced to a fraction of their former extent.

Historically, culverts were designed by civil engineers to maximize flow capacity and minimize pipe size in order to create the most economical structure for developers, transportation authorities, and municipalities.  The unfortunate by-product of such a design approach is that water velocity through culverts is extremely high, often running in supercritical flow, even during base flow conditions, and the smooth and featureless surfaces in the structure make it extremely difficult to navigate.  To add insult to injury, the high velocity flows also scour and erode the stream channel immediately downstream of the culvert, leaving the pipe too high out of the new channel (“perched pipes”) for organisms to pass.  Downstream water dependent organisms cannot pass upstream to new habitat, and those populations upstream become extirpated due to downstream migration and mortality, and the lack of an ability to return or be replaced.  A study of impacts of fragmentation on brook trout is ongoing by the USGS Conte Anadromous Fish Research Center (USGS CAFRC) and others, and a study recently completed documented the impacts of fragmentation of local populations provides an informative view of the blockage potential of culverted streams.

There is hope in the re-connection of stream habitat through new research and initiatives developed since 1999.  One such approach is through the Stream Simulation design originally developed in its present form at the Washington State Department of Fish & Wildlife and adopted by the US Forest Service, US Fish and Wildlife Service, as well as others, and was also adopted shortly thereafter and refined by the University of Massachusetts, Amherst Extension (Stream Continuity model) for use in Northeastern States (initially in the Massachusetts River and Stream Crossing Standards, and then adopted in similar form by surrounding states).  Through the Stream Simulation/Continuity method, a culvert is not simply measured in terms of hydraulic efficiency, but also in terms of ecological and biological efficiency.

In the most basic terms, Stream Simulation (Continuity) requires a crossing that has a minimum width of the bankfull flow of the natural channel upstream and downstream, plus more width to allow passage of terrestrial organism passage such as reptiles and amphibians (in the UMASS model the increase in width is 20% wider than bankfull, but in the current Washington State model they use 20% plus 2 feet).  The other part of the design requirement is an opening area to length ratio to allow the maximum amount of natural light penetration into the culvert (openess ratio), as many organisms, such as fish, are too intimidated to travel through dark culverts.  Other design requirements include the use of slopes and velocities that allow for fish passage, and roughness (i.e. placement of natural substrate) to also slow down the flow.

The key challenge for the retrofitting of culverts to be more passable is cost.  As with any civil engineering project, the larger it is, the more expensive.  To replace a 36 inch diameter culvert with a 10-14 foot wide structure could increase the cost by 10-fold.  However, there are ways in completing an economic analysis to justify the costs.  For example, most culverts were historically only designed to pass storms up to the 25-year event, but in even more cases, never were sized by engineers.  A larger culvert will increase its capacity and reduce overtopping events that would require road closings and worse, cause the roadway to collapse.  Road closings require emergency management and road crews to set up detours and slowing down commerce, or worse require repetitive reconstruction efforts that, over time, may exceed the cost of installing a Stream Simulation designed culvert.


Same culvert as in photograph above, after the retrofit using Culvert Simulation. ©Princeton Hydro.

Other ways of encouraging installation of these larger and passable culverts is through the permitting process.  In New England, the US Army Corps of Engineers, allows for a by-pass of a formal review for their approval if the Stream Simulation guidelines are followed. This approach can save a significant amount of time to fast-track a retrofit.  To complement the Corps’ permit facilitation process, the states of Connecticut, Massachusetts, New Hampshire, and Vermont, have developed stream crossing guidelines to meet the Corps’ permit by rule compliance.  These states have even instituted state level regulations requiring aquatic organism passage via the Stream Simulation model.

Princeton Hydro was contracted to design a culvert retrofit to replace a 36 inch diameter culvert with a 12 foot wide arch culvert on a tributary of West Brook which is being monitored as part of the USGS CAFRC research project in Massachusetts.  This retrofit will be used to assess the increase in efficiency of headwater stream accessibility by local brook trout populations.

It would appear that the Stream Simulation or Continuity model is catching on, however, there needs to be more outreach and changes to existing rules in other regions of the US.  Further studies, such as that being conducted by USGS and their partners, will determine the true benefits of increasing culvert fish passage efficiency and bolster the economics of protecting fish populations for future generations.
Geoffrey M. Goll, P.E.
Vice President and Founding Partner

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