Reasons to Rethink the Muddy River Restoration Project:  Dredging Impacts

This addresses one aspect of a project (dredging), in two areas of impact (trees and groundwater levels), in one section of the total project area.  Specifically, the Muddy River Restoration Project.

Geographically, the Muddy River is situated in Eastern Massachusetts connecting Jamaica Pond in Jamaica Plain to the Charles River in Boston.  ItÕs a meandering river running for approximately three miles through suburban and urban areas, serving as municipal boundary, parkland, and wetland, and its use has changed over time, reflecting the values and needs of the encroaching populations.   The riverÕs watershed is a sub-watershed within the Charles River watershed.  The watershed that feeds the Muddy River receives water from springs, ponds, reservoirs, as well as storm drains and runoff from roadways, paths, sidewalks, ball fields, parking lots, lawns and rooftops, all of which contain many possible combinations of various toxics, nutrient overloads and bacteria.

For the past eleven years, since the riverÕs flooding from an unusual rain event, the municipalities  (Boston and Brookline) which share Muddy River and upstream ponds, together with the State and the Army Corps of Engineers have been shaping a plan to alleviate the threat of future flooding by means of a dredging and daylighting project.  The dredging will widen and deepen the river (and ponds) to increase water holding capacity, and the daylighting will return a portion of the river to the surface.  That is, open an area that had been channeled underground to accommodate a parking lot (across from the Landmark Center on Brookline Avenue, then Sears), freeing the river from the choking constriction of the undersized culverts used during that construction.  This choke-hold is what is credited with causing the bulk of the flooding damage to the Kenmore T Station in 1996.

If done with farsighted considerations the daylighting accompanied by construction of a bridge rather than culverts would likely decrease the threat of flooding to a sufficient degree, but the plan for the Muddy River Restoration Project doesnÕt stop there.  The project plans also call for the dredging of the river from Boylston Street to WardÕs Pond, and in some areas along that length, bank-to-bank.  While I have studied some of the effects of dredging on environmental values of the project area in another report (An Environmental Values Assessment of the Muddy River Restoration Project), here I would like to concentrate on a couple of other aspects of dredging impacts and to limit the area of the discussion to those areas known as the Fens and the Riverway – areas between Boylston Street and Brookline Avenue.

The first exploration considers the groundwater, and asks whether the impacts of dredging on groundwater levels, isnÕt an area that requires an additional environmental impact assessment.  This area is at sea level, and before the Charles River Dam was constructed, was a salt marsh subject to tidal fluctuations.  The water table is high.  High enough to be at the surface in the Spring and notorious for delaying the drying of soils in the Victory Gardens, much to the chagrin of the community gardeners there.  It is also high enough to ensure that the wooden pilings supporting buildings in Back Bay are preserved from dry rot, thus keeping the buildings upright. 

This area is part of what is known as a Groundwater Conservation Overlay District (GCOD).  Maintaining sufficient groundwater levels takes constant monitoring by means of scores of wells installed throughout the district.  When depletion is detected an investigation of the source of groundwater loss is undertaken.   Groundwater in the overlay district has been historically depleted by diversions, whether from being used to dilute and move sewage, or from urban infrastructure disrepair.  The disrepair can take the form of cracked sewer pipes and leaky joints that allow groundwater infiltration, or in the form of sump pumps in building basements, all of which take groundwater and relocate it far from where it would be able to recharge itself.  From Back Bay ground water, to the Atlantic Ocean being taxied by the sewer system to the Deer Island Water Treatment facility.  The MBTA also pumps ground water from its tunnels and underground transit infrastructure.  Ironically ground water levels have also fallen because leaking water supply pipes have been fixed, foiling recharge from water from the middle of the state (the Quabbin Reservoir, BostonÕs drinking water supply) to BostonÕs underground.  If a little leak here, and a little pumping there causes ground water levels to drop to problematic levels and damage buildings set on pilings in a filled parcel of land, how will dredging that will deepen the Muddy River by one to six feet impact a fragile water table?  (When I asked gardeners at Victory Gardens in the Fens what they thought about the proposed dredging, some have responded that it will cause the water table to fall and that means earlier planting.  Goody!)  However the building repairs and outright building loss in the area have been costly.  Property owners have needed to invest hundreds of thousands of dollars in piling replacement and building repairs.

Since dredging is known to lower water tables, and the depth of dredging for this project will range from one to six feet, should it be a concern that deepening the river will cause a precipitous lowering of the water table and thus bring about multiple building destabilizations?  Would it be prudent to undertake the impact studies far in advance of the dredging? 

The second area of concern is the impact of dredging on trees and tree health.  A fallen water table is known to adversely affect and outright kill trees by putting the needed water out of the reach of their root systems.  The stretch of river between the Victory Gardens and the Landmark Center contains a riparian area consisting of a conservatively estimated several hundred trees (I was not able to do an inventory before this writing, but I think itÕs likely thereÕs over a thousand trees growing there.), plus dozens more in the surrounding parkland (which is within the riparian zone as well).  That strip of green which buffers the Muddy River from the encroaching streets is very narrow.  Interestingly, the feeling one has while walking along the river is that the traffic is at a distance, thus illustrating how effective trees are in mitigating the drone, dust, and view of urban hubbub, as well as the gift Frederick L. Olmsted had for urban landscape design.  These are a few of the more obvious benefits of trees in the landscape, but there are others.

Trees also mitigate flooding in a number of ways.  Their leaves hold water on their surfaces, lessening the amount of water that reaches the ground at one time, as well as the degree of intensity with which the rain hits the ground.  Trees also hold the soil and lessen erosion, thus stabilizing river banks.  They bring groundwater closer to the surface.

Trees however are sensitive to environmental stresses, and these stresses can damage and kill a tree.  Many of the trees in the riparian and park areas are currently showing signs of distress.  Some of those signs, such as dead branches and leafless tops, may be due to the urban environment, such as air and water quality.  It could also be the result of compaction, resulting from police and park patrols being conducted from cars and trucks being driven on the pedestrian paths. (It takes very little pressure to destroy delicate feeder root ability to nourish a tree.)  The fluctuating river and groundwater levels could also be having an adverse impact.  ItÕs likely a combination of all of the above, plus climate change.  Trees are not getting the period of dormancy theyÕve evolved with in this particular geography.

As noted above, tree roots are particularly sensitive to damage.  They grow laterally and shallowly from the tree and extend well beyond the drip-line, by as much as two to three times beyond, which is why compaction is an issue.  Tree roots both anchor and support the tree, and on slopes actually grow more roots on the downhill side of the tree.  Trees need healthy roots to guarantee adequate water and nutrients.  Tree roots can sustain some damage and the tree will survive, but only if it is undertaken to actively assist the tree in recovery.  Tree experts vary in estimating the amount of damage which can be withstood by a particular tree.  The range is between thirty and fifty percent, and varies depending on the species of tree.  Very few will survive as much as fifty percent, and the ideal is zero percent damage.  The effects of damage on tree health may be immediately apparent, or not show for a few years.

Trees can be damaged by having roots severed, or the soil over them compacted by construction equipment, (the top four inches of soil contain the critical fine feeder roots on which the tree depends) as well as by equipment wounding the trunk or branches.  They can also be negatively impacted by the drop in the water table, and dust on the leaves.  These would all be present with dredging activities.  In particular, because of the slope of the riparian area of the Muddy River, the roots likely follow the river bank closely, both laterally and parallel, and with the heaviest feeder-root growth nearest the river.  That would indicate that bank-to-bank dredging activities could be expected to take a heavy toll on the critical support system of the riparian trees.  In an added note, if tree roots stand a chance of healing, each one needs to be cut cleanly not ripped or shredded, which would mean a lot of TLC for each impacted tree.

When trees are removed or damaged in a landscape and are to be replaced, the ratio is not one-to-one.  That is, not one tree removed and one tree replaces it.  Scales of replacement vary, some more conservative than others.  They are based on caliper inch-per-caliper inch replacement measurements.  So a tree to be replaced that has a twenty inch caliper would need to have twenty one inch, or five four inch, or ten two inch, etc. trees to take its place.

A hypothetical look at the trees which could be impacted in the process of dredging Muddy River might, conservatively, look something like this:  If five hundred trees in the riparian area were expected to be removed or damaged, and they range from two to twenty inches, averaging out at eleven inches each, then fifty-five hundred inches in tree width would be needed to replace them; translating into fifty-five hundred one-inch, or twenty-seven hundred plus two-inch, or eleven-hundred five-inch trees, and so forth, planted to compensate for the loss.  This leads to the question, how many trees can we afford to lose?  If this project goes forward as outlined in the plans, where will there be room to plant replacement trees, how will we pay for them, or are we to do without?

Another consideration is that since trees absorb water from the soil they increase the soils ability to hold water, therefore removing and then not adequately replacing trees could actually increase flooding.  Even if the rate of replacement plantings fits that scale above, small trees have small canopies, and scattered plantings do not compensate for the concentrated thirty foot spread of a mature tree.  Could dredging have as an unintended consequence worse flooding due to tree loss?

Without the trees that are there, and the shade they offer, the surface water and bank temperatures can be expected to rise.  Increased water temperatures lessens the waters ability to hold oxygen, thus decreasing water quality and impacting those aquatic species which require highly dissolved oxygen to survive. With the combined effects of climate change and urban stress, including vandalism, what will the survival rate of replacement trees be?

These are serious potential impacts, yet, and I may have missed it, there are no indications of these considerations in reports filed over the years on this project.  This project has been in discussion and planning for eleven years, the environmental impact assessment needs to be reconsidered in light of the latest data on ground water levels and climate change impacts.  It is imprudent to undertaken the dredging until a full thorough assessment of impacts on existing tree health, as well as the sheer scale of replacement and all that attends that.

            There are also some added concerns that need to be address when considering the area to be daylighted.  While opening up the river and constructing a bridge to replace the narrow culverts should remedy the rivers ability to overflow into the subway tunnel, we need to ask how water quality may be impacted.  The area to be newly re-exposed to the surface is to encounter a much changed environment.  The street configuration has not changed appreciably, but the vehicular traffic has grown exponentially.  The little patch that was river, then parking lot, now sloped grass island is surrounded by three to four lanes of continual heavy traffic and traffic jams, creating a lot of pollution taking the form of concentrated runoff as well as airborne particulates settling in the river, or the occasional overturned car or truck.  Careful consideration needs to be given in protecting the area from vehicular intrusion, as well as plantings that will be able to adequately screen or divert the particulates.  It would be an opportunity to design alternatives to catch basins and outfalls that would normally be expected to have outfalls along the river in order to ensure that Muddy River water quality does not deteriorate further as the result of "improvements."   

 

(Respectfully submitted to the commission)

 

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