Charles River Flood Model Part II: Nature-Based Solutions
Managing Future Flooding in the Upper and Middle Charles River Watershed with Nature-Based Solutions
Future Flooding in the Charles
Twenty communities that are part of the Charles River Climate Compact (CRCC) teamed up to develop the Charles River Flood Model (CRFM), a watershed-scale visualization that forecasts expected flooding under different climate conditions and models flood mitigation strategies of various nature-based solutions for the entire 174,080 acres of the Upper and Middle Charles River Watershed.
Click on the button below to view Part I of the Charles River Flood Model: Mapping Future Flooding in the Upper and Middle Charles River Watershed
To obtain input on which flood mitigation strategies to assess, the team conducted surveys to gain input from the public and municipal project partners. The three categories prioritized by both the public and the project team were:
- Green Stormwater Infrastructure
- Land conservation
- Less paved/impervious surfaces
What are Nature-Based Solutions (NBS)?
NBS are adaptation measures focused on the PROTECTION, RESTORATION, and/or MANAGEMENT of ecological systems to safeguard public health, provide clean air and water, increase natural hazard resilience, and sequester carbon. Incorporating NBS in local planning and design projects produces long-term solutions that benefit human and natural systems. (Source: MA Municipal Vulnerability Preparedness Program)
Examples of Nature-Based Solutions:
Graphics example of Nature-Based Solutions including land conservation, wetland restoration or protection and tree canopy
What is Green Infrastructure/Green Stormwater Infrastructure?
Green Infrastructure (GI) or Green Stormwater Infrastructure (GSI) helps STORE, FILTER and ABSORB stormwater where it falls and reduces flooding impacts. It uses plant or soil systems, permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater, all of which reduce runoff to sewer systems or surface waters. Learn more about Green Infrastructure.
Graphics example of different kinds of GSI systems: Tree filter boxes, rain gardens, green roofs and bioswales, that help mitigate local flooding impacts
Based on the three prioritized categories, the team modeled eight flood mitigation scenarios using different nature-based solutions
Nature-Based Solution Scenarios Modeled
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Scenario 1: Green Stormwater Infrastructure
Scenario 1A was designed to evaluate the potential flood mitigation benefits of using Green Stormwater Infrastructure (GSI) to store runoff in, under, and near impervious surfaces where the majority of runoff is created.
This scenario specifically modeled GSI that would store the equivalent of the 2070 2-year storm event (approximately 4.5 inches of precipitation) from 50% of all impervious areas within the Charles River watershed.
Flood reduction benefits for all NBS scenarios were evaluated for the 2- and 10-year storm events under both baseline and 2070 climate scenario.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 1A during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 1A would reduce total runoff by 26% (for the future 2-year storm compared to No Action) and 12% (for the future 10-year storm compared to No Action), with a total runoff reduction of more than 1,650 million gallons (MG) for both storm events. Total inundated areas would be reduced by 16% for the 2-year storm event and by 5% for the 10-year storm event.
Figure on the right shows impervious surfaces in several sub-basins where additional GSI was considered.
Changes by Sub-basin
GSI in Scenario 1A will reduce inundation area in Seaverns Brook by 19%, Rock Meadow by 15%, and Indian Brook by 15%.
All sub-basins will experience reduced total runoff ranging from 2% (Powisett Brook) to 30% (Charles River Watertown).
Figure on right shows the percent change in total inundated areas for Nature-Based Solution 1A, by watershed sub-basin, during the 2070 10-year storm event, in comparison to No Action.
Local Flood Reductions Using Scenario 1A
Swipe left on the map to see the changes in inundated areas and flood depths in Newton/Dedham if Scenario 1A was implemented for the Present Day 10-year storm events.
Scenario 1B was designed to evaluate the potential flood mitigation benefits of using Green Stormwater Infrastructure (GSI) to store runoff in, under, and near impervious surfaces where the majority of runoff is created.
This scenario focuses on large parcels only, with the expectation that targeting large impervious parcels could be a cost- and time-effective approach to adding flood storage into the landscape.
This scenario modeled storing the equivalent difference between the 2070 25-year and 2070 2-year storm events on all public and private parcels larger than 5 acres which include impervious surface.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 1B during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 1B would reduce total runoff by 4% (for the future 2-year storm compared to No Action) and 2% (for the future 10-year storm compared to No Action), with a total runoff reduction of more than 250 million gallons (MG) for both storm events.
Figure on the right shows locations of impervious surfaces on public and private parcels with atleast 5 acres of impervious surfaces
Changes by Sub-basin
GSI in Scenario 1B will reduce the total inundation area of Charles River (Watertown) sub-basin by 18% and by 5% for Lowder Brook.
- 27 sub-basins will see no or minimal reduction in inundation area.
Lowder Brook and Mine Brook will experience the largest total runoff reductions (5%) from Scenario 1B.
- 12 sub-basins will experience no reduction in total runoff, as very few of the large impervious parcels modeled were located in those sub-basins.
Figure on the right shows map of the percent change in total inundated area for Scenario 1B, by sub-basin, during the 2070 10-year storm event, in comparison to No Action.
Local Flood Reductions Using Scenario 1B
Swipe left on the map to see the changes in inundated areas and flood depths in Newton/Dedham if Scenario 1B was implemented for the 2070 10-year storm events.
Scenario 2: Reduce Impervious Cover
Scenario 2 was designed to evaluate the potential mitigation benefit of reducing the quantity of impervious surfaces throughout the watershed to reduce stormwater runoff
This scenario specifically modeled reducing the percent of effective impervious cover in all subcatchments by 25%.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 2 during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 2 would reduce total runoff by 9% (for the future 2-year storm compared to No Action) and 5% (for the future 10-year storm compared to No Action), respectively. Scenario 2 would also reduce watershed-wide inundation areas by 7% (2-year) and 2% (10-year).
The figure on the right shows the percent change in total inundated areas for Scenario 2, by sub-basin, during the 2070 10-year storm event in comparison to No-Action.
Changes by Sub-basin
Charles River (Dover to Wellesley) and Lowder Brook will both experience an 8% reduction of inundated area through Scenario 2.
Cheesecake Brook will experience a 14% reduction in total runoff while the Charles River (Wellesley to Stony Brook) sub-basin will experience a 12% reduction of total runoff.
Flood Reductions Using Scenario 2
Swipe left on the map to see the changes in inundated areas and flood depths in Waltham if Scenario 2 was implemented for the present day 10-year storm events.
Scenario 3: Upland/Pond Storage
Scenario 3 was designed to evaluate the potential flood mitigation benefit of increasing flood storage capacity of existing lakes and ponds throughout the watershed.
This scenario modeled an additional 1 to 3 feet of flood storage capacity to wetlands and open waterbodies greater than 20 acres in the watershed.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 3 during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 3 will reduce the total inundated areas by 2% for both the future 2- and 10-year storm events, compared to No Action. No reduction in total runoff is observed for the 2-year storm event with Scenario 3, and only a 1% reduction is observed for the 10-year storm event.
The figure on the left shows locations of non-reservoir surface waterbodies bigger than 20 acres that were evaluated in Scenario 3.
Changes by Sub-basin
In Scenario 3, Indian Brook is expected to experience a 40% reduction of inundated area, Charles River (Dover to Wellesley) by 6%, and both Rock Meadow Brook and Stop River by 5%.
8 sub-basins are expected to experience significant descreases in total runoff, ranging from 1% (Indian Brook, Charles River) to 5% (Lowder Brook) reductions.
The map on the left shows percent change in total inundated area for Scenario 3, by sub-basin, during the 2070 10-year storm event, in comparison to No Action.
Flood Reductions Using Scenario 3
Swipe left on the map to see the changes in inundated areas and flood depths in Natick if Scenario 3 was implemented for the 2070 10-year storm events.
Scenario 4: Wetland Restoration
Scenario 4 was designed to evaluate the potential flood mitigation benefit of restoring or increasing existing wetlands throughout the watershed so that surface area increases by a combined 20%
This scenario was modeled by adding buffers around existing Massachusetts Dept. of Environmental Protection (MassDEP) Wetlands GIS database, to reach a total wetland area 20% more than the current wetlands area in the watershed.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 4 during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 4 would reduce inundated areas across the watershed by 4% for the future 2-year storm event compared to No Action only. No reduction is observed for the 10-year storm event. Total runoff will be reduced by 2% for the 2-year and 1% for the 10-year storm events, respectively.
The figure on the right shows existing MassDEP-identified wetlands and the theoretical additional wetland incorporated into Scenario 4.
Changes by Sub-basin
In Scenario 4, Davis Brook is expected to experience a 7% reduction of inundated area. Six other sub-basins will have a 1% reduction, and the remaining will have no change.
All sub-basins, excep Seaverns Brook (2% reduction) will expereince a reduction of 1% or less in total runoff from Scenario 4.
Figure on the right shows the percent change in total inundated area for Scenario 4, by sub-basin, during the 2070 10-year storm event, in comparison to No Action.
Flood Reductions Using Scenario 4
Swipe left on the map to see the changes in inundated areas and flood depths in Medway and Norfolk if Scenario 4 was implemented for the 2070 10-year storm events.
Scenario 5A: Lack of Land Conservation
Unlike the other scenarios, Scenario 5A was designed to evaluate the potential increase in flooding that would be expected to occur with increased development in the watershed, and conversely, the flood mitigation benefit of minimizing development
This scenario specifically modeled 15% of the remaining undeveloped and unprotected land area in the watershed being developed show the benefit of limiting future development and protecting flood control benefits of natural lands.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 5A during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Scenario 5A would increase inundated areas by 21% (for the future 2-year storm compared to No Action) and 8% (for the future 10-year storm compared to No Action). Total runoff for the watershed would increase by 26% for the 2-year storm event and 14% for the 10-year storm event.
The figure on the left shows the 15% of the remaining undeveloped and unprotected land that were modeled to be developed for Scenario 5A
Changes by Sub-basin
Charles River (Stony Brook to Watertown) is expected to have the largest increase of inundated area with 29% increase, followed by South Meadow Brook with a 24% increase, and Rock Meadow Brook with a 23% increase.
- 8 sub-basins will experience little to no change in inundated area.
All sub-basins will see an increase in total runoff by atleast 2%. Mill River and Seaverns Brook will have the largest increases in total runoff with 35% for Mill River and 33% for Seaverns Brook.
Map on the left shows the percent change in total inundated area for Scenario 5A, by sub-basin, during the 2070 10-year storm event, in comparison to No Action. Darker blue indicates an increase in flooding.
Flood Reductions Using Scenario 5A
Swipe left on the map to see the changes in inundated areas and flood depths in Needham and Roxbury if Scenario 5A was implemented for the Present Day 10-year storm events.
Scenario 5B: Regulatory
Scenario 5B was designed to evaluate the capacity of increased stormwater retention requirements on new development to mitigate the increased flooding expected as a result of the new development.
This scenario specifically modeled the mitigating capacity of storing the difference between then 2070 25-year and 2070 2-year rainfall depths on 50% from the assumed new impervious surfaces as a result of new development. This strategy aimed to offset impacts of future development by requiring GSI in any new developments.
Regulatory example is based on City of Cambridge's Stormwater guidance .
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Scenario 5B during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
While Scenario 5B incorporated flood mitigation measures in response to increased development in the watershed, the mitigation strategy is not sufficient to offset the impact of new, additional impervious surface in the watershed.
Watershed-wide, total inundated areas would increase by 12% (for the future 2-year storm compared to No Action) and 5% (for the future 10-year storm compared to No Action), respectively, compared to No Action. Total runoff would increase by 11% for the 2-year storm event and by 6% for the 10-year storm events.
Figure on the right shows percent change in total inundated area for Scenario 5B, by sub-basin, during the 2070 10-year storm event, in comparison to No Action. Darker blue on map shows increased inundated areas.
Changes by Sub-basin
Mill River will experience the largest increase of inundated area with an 18% increase, followed by a 15% increase for both Rock Meadow Brook and Shephers Brook.
- 12 sub-basins will experience no change in inundated area
All sub-basins will experience an increase in total runoff by atleast 1%. Mill River and Seaverns Brook will experience the largest total runoff increase with 17% and 16%, respectively.
Flood Reductions Using Scenario 5B
Swipe left on the map to see the changes in inundated areas and flood depths in Needham and Roxbury if Scenario 5B was implemented for the Present Day 10-year storm events.
Scenario Alternative B: Dam Removals
Alternative B was designed to evaluate the potential flood mitigation benefit of removing unnecessary dams within the Charles River watershed to lower flood levels upstream.
This scenario specifically modeled the removal of 15 dams sitting on the Charles River.
Dams were identified as candidates for removal by identifying dams listed in the MassGIS database with a "Recreation" purpose, eliminating dams used for flood control and drinking water supply reservoirs.
Summary of inundated areas (acres) and total runoff for Nature-Based Solutions Alternative B during the 2070 2- and 10-year storm events on a watershed-scale, and the percent changes from No-Action.
Watershed-wide, Alternative B would reduce inundated areas by 5% for the future 2-year storm event compared to No Action, and by 1% for the future 10-year storm event compared to No Action. There are no expected changes in total runoff volume for Alternative B as the land surface does not change, thus resulting in no change to how runoff occurs.
The figure on the right shows the 15 dams that were assumed to be removed under Alternative B.
Changes by Sub-basin
Mill River is expected to experience an 8% reduction of inundated area based on the 2070 10-year storm event.
Charles River Headwaters will experience a 7% reduction of indundated area based on the 2070 10-year storm event.
Figure on the right shows the percent change in total inundated area for Alternative B, by sub-basin, during the 2070 10-year storm event, in comparison to No Action.
Flood Reductions Using Scenario Alternative B
Swipe left on the map to see the changes in inundated areas and flood depths in Medway and Norfolk if Scenario 5B was implemented for the Present Day 10-year storm events.
Watershed Wide Flooding Changes Under Proposed GI Scenarios
At the watershed scale, NBS Scenarios 1A, 2 and 3 had the largest reductions in total watershed volume as seen in the graph above.
How Effective are Nature-Based Solutions?
Figure above shows the effectiveness of NBS, on a sub-basin basis, in terms of total watershed runoff volume during the 2070 10-year storm event. The figure shows that some scenarios were more effective for one sub-basin versus another (Scenario 1A (blue line) is more effective at reducing total runoff volume for Charles River (Watertown) sub-basin than it was for Hobbs Brook).
Priority Sites for NBS in the Watershed
Hardy Pond, Waltham
Hardy Pond, Waltham. Click to expand.
40+ acre pond with adjacent wetland systems that connects to the Chester Brook tributary of the Charles River.
Oakland Park, Medway
Oakland Park, Medway. Click to expand.
Popular recreational field complex with soccer fields, playground and parking areas.
Albemarle Field, Newton
Albemarle Field, Newton. Click to expand.
Large athletic field/recreation complex for soccer, baseball, tennis and basketball.
Concept Plan for Hardy Pond, Waltham created by Weston & Sampson
Concept plan for Oakland Park, Medway created by Weston & Sampson
Concept plan for Albemarle Field, Newton created by Weston & Sampson
Read the final Charles River Flood Model Climate Adaptation & Flood Mitigation Implementation Plan for an in-depth dive on the flood model and report
View the Charles River Flood Model Results
The Charles River Flood Model Results Viewer allows you to preview flooding impacts from various storm events within the watershed. The viewer also demonstrates the potential flood reduction benefits from the installations of green infrastructure systems and upland storage.
To view a specific area, click the map to interact. Zoom in with the +/- buttons in the top left corner. In the "Model Results" tab on the right side, select the storm event or flood reduction scenario you would like to view. Toggle the scenarios on and off to view the change in flooding. For the full web mapping experience, click the launch button in the top right corner.
Charles River Flood Model Results Viewer
FAQ
Why is the model only for the Upper and Middle watershed, and not the Lower watershed?
Detailed stormwater system models for the Lower Watershed, including Boston , Cambridge , and Somerville , have already been developed and published.
Is the Charles River Flood Model Accurate?
The Charles River Flood Model uses several ways to verify the Model's accuracy. Read more in our Model Development section or the final report here ! Since the simulated peak discharge rates and total flood volumes in the Charles River watershed matched historical March 2010 values at multiple locations in the upper, middle, and lower reaches of the watershed, it indicates that the Model is well-suited to simulate flooding impacts throughout the watershed during a wide range of storm events.
How much worse will flooding get in the Charles with climate change?
Climate change will bring more extreme storm events to the Charles River Watershed and can add up to 78% more flooding (+2,733 acres in a 2-yr storm event) and up to 61% more in total runoff volume (+11,281 million of gallons in a 100-yr storm event).
