feb 11 2014 public meeting
DESCRIPTION
February 11, 2014 public meeting presentation for three proposed stormwater facility management projects off of Cabin Branch of Great Seneca Creek. (pdf file)TRANSCRIPT
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Cabin Branch Stormwater ManagementStormwater Management
Retrofit Projects
Quail Valley Pond #1il ll dQuail Valley Pond #2
Strawberry Knoll Facility
Concept Design PresentationF b 11 2014February 11, 2014
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T d ’ A dToday’s Agenda
Sources of Water on Earth Montgomery County backgroundWh t i W t h d & R ff? What is a Watershed & Runoff?
Intro to Stormwater What the County is Doing to Protect Our Streams What the County is Doing to Protect Our Streams Goals of the Project Proposed Pond Retrofit p Questions/Comments
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Sources of Water
About 97% is salt water About 2% is frozen Only 1% is available for drinking water Only 1% is available for drinking water
Across the country, most potable water is from groundwater In Maryland, most is from surface water
Potential for greater impacts from runoff in Marylandg p y
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Montgomery County, MD 500 sq. miles 970,000 people
Second only to Baltimore City within Maryland in average people per Maryland in average people per square mile
184 languages spoken About 12% impervious surface overallp
About the size of Washington DC Over 1,500 miles of streams Two major river basins:
P Potomac Patuxent
Eight local watersheds District of Columbia
I i N t ll i t t
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Impervious: Not allowing water to soak through the ground.
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What is a Watershed? A watershed is an area from which the water above and below ground above and below ground drains to the same place.
Different scales of watersheds:watersheds: Chesapeake Bay Eight local watersheds Neighborhood (to a storm drain)
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h ff?What is Runoff?Water that does not soak into the ground becomes surface runoff. This runoff flows over hard surfaces like rooftops, driveways and parking lots collecting potential contaminants and flows:
• Directly into streams• Into storm drain pipes, eventually leading to
streams• Into stormwater management facilities, then
streams
Two Major Issues:V l /Ti i f R ffVolume/Timing of Runoff
Water Quality6
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What is the County doing toprotect our Streams?
Must meet regulatory requirements Federal Clean Water Act permit program MS4 = MMunicipal SSeparate SStorm SSewer SSystem MS4 = MMunicipal SSeparate SStorm SSewer SSystem
Applies to all large and medium Maryland jurisdictions County programs
Restore our streams and watersheds Add runoff management
Meet water quality protection goals Reduce pollutants getting into our streams
Educate and engage all stakeholders Individual actions make a difference
Focus on watersheds showing greatest impacts
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MS4 P i Wh i i ?MS4 Permit: What is it? Montgomery County is responsible for:Montgomery County is responsible for:
• What goes into our storm drain pipes • What comes out of them• What flows into the streams
Requires additional stormwater management for 20 (percent of untreated impervious surfaces (4,292 acres =
6.7 square miles). That’s about three times the size of Takoma Park.
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O ll G l f h P jOverall Goals of the Project Provide water quality treatment and downstream channel Provide water quality treatment and downstream channel
protection to meet MS4 program requirements. Improve ecological value of existing stormwater
management facilities management facilities. Improve existing landscaping and plant diversity of
existing facilities. U d i ti f iliti t l ith f t d Upgrade existing facilities to comply with safety and
design standards. Utilize existing open space to provide stormwater
t management.
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P j t L tiProject Location
CabinBranch
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Quail Valley Pond # 1Q ySWM Retrofit
P j t O iProject Overview
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D i ADrainage Area 9.24 acre drainage 9.24 acre drainage area to pond
51% impervious
L d i l d Land cover includes roadway, sidewalks, manicured lawns/landscaping. a s/ a dscap g.
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Existing Conditions Constructed in the early 1980s
Fully developed drainage area
Does not provide water quality functions
High groundwater exists in bottom of facility
Does not meet current safety and design standards (materials and conveyance)
Sinkholes have recently developed in embankment
Maintenance access is inadequate
Minor sediment deposition from upstream erosion13
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E i ti Q il V ll P d # 1Existing Quail Valley Pond # 1
View of facility from Centerway Rd Bottom of facility showing base flowView of facility from Centerway Rd Bottom of facility showing base flow
14Existing substandard riser. Sinkhole resulting from riser
degradation.
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Grade bottom of pond and eastern bank
Retrofit Design Details Grade bottom of pond and eastern bank.
Create a 3.5’ deep wet pool.
Remove and replace existing riser and outflow pipe.
Reconstruct portion of existing embankment. p g
Remove small diameter trees within limits of work.
P id th f i t Provide access path for maintenance.
Re‐vegetate pond and plant additional trees.
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P d P d R t fitProposed Pond Retrofit
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Plan View
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Proposed Pond Retrofit
Profile
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Quail Valley Pond # 2Qua a ey o dSWM Retrofit
P j O iProject Overview
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D i ADrainage Area 48.9 acre drainage area to pond
24% impervious
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Existing Conditions
Constructed in the early 1980s
Fully developed drainage areay p g
Dry detention pond constructed in a stream valley
Very few ecological or water quality benefitsVery few ecological or water quality benefits
Good condition, but riser is nearing end of service life
Maintenance access is inadequate Maintenance access is inadequate
Minor sediment deposition from upstream erosion
Degradation and incision of downstream channel Degradation and incision of downstream channel
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E i ti Q il V ll P d # 2Existing Quail Valley Pond # 2
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Enlarge the storage volume to treat 50% of the
Retrofit Design Details Enlarge the storage volume to treat 50% of the Water Quality Volume (WQv)
Add a sand berm to increase infiltration
Grade an additional storage basin in existing open space adjacent to stream banks
Safely pass larger storms, including the 100‐year Safely pass larger storms, including the 100 year storm
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Retrofit Design Details
Install a forebay at the top of the pond to improve maintenance
Remove existing risers and replace with cobble riffle structures
Restore downstream channel using step poolsRestore downstream channel using step pools
Revegetate pond with native plants
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P d P d R t fitProposed Pond Retrofit
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Proposed Pond Retrofit
Profile of Proposed Retrofitp
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Cross‐Section of Proposed Retrofit
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Stormwater Pond RetrofitStormwater Pond RetrofitDuring Constructiong
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Stormwater Pond RetrofitStormwater Pond RetrofitWithin 1 Year After Construction
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Stormwater Pond RetrofitStormwater Pond RetrofitWithin 5 Years After Construction
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Strawberry KnollStrawberry KnollUnderground SWM Facility
Project Overview
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D i ADrainage Area 20.5 acre drainage20.5 acre drainage area to facility
37% impervious
L d i l d Land cover includes roadway, sidewalks, manicured lawns, open space, and ope space, a dlandscaping.
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Existing Site Conditions
Parcel is owned by the Flower Hill Central Corporation
Parcel provides open space for Flower Hill Communityp p p y
Two stormdrain systems connect under open space
Flow in existing stormdrain is not treated for Water Quality orFlow in existing stormdrain is not treated for Water Quality or Channel Protection
Space is available on site to provide an SWM facility
Site is accessible from Strawberry Knoll Road
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E i ti O SExisting Open Space
Location of Proposed SWM Facility. Open space south of proposed facility.
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Location of proposed construction and maintenance access.
Existing inlet which SWM system will connect to.
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Underground gravity driven treatment system
SWM Design Details Underground gravity driven treatment system. Three components: pretreatment, storage, and treatmenttreatment. Pretreatment simplifies and reduces the need for maintenancemaintenance.
Storage System stores stormwater until filtered. Filter replaces natural functions depleted with development Filter replaces natural functions depleted with development.
Provide stable vegetated access path for future maintenancemaintenance.
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P d SWM D iProposed SWM Design
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Plan View
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Proposed SWM Design
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Profile
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Grass Pavers
UrbanGreen Grass Paver Detail
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Stormwater Treatment
Vortechs Pretreatment System Stormfilter System
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Underground SWM FacilityUnderground SWM FacilityDuring Constructiong
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Storage system being installed Watertight joint being sealed
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Q il V ll P d # 1 C t ti AQuail Valley Pond # 1 Construction Access
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Q il V ll P d # 2 C t ti AQuail Valley Pond # 2 Construction Access
Access from CenterwayRoad Cl id h ill lik l Clear width will likely require tree removal and gradinggrading
Tree protection where needed
Mulch placed on path and removed after
i
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construction
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St b K ll C t ti AStrawberry Knoll Construction Access
Access from Strawberry Knoll Road
ll b b l d Access will be stabilized to prevent sediment transport to Strawberry Knoll RoadStrawberry Knoll Road
Curb ramp and grass pavers will be provided at final stages of Location of proposed construction and
construction. Location of proposed construction and maintenance access.
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Construction Access (Example)
During Construction After ConstructionDuring Construction After Construction
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Reforestation
Attractive native trees and shrubs trees and shrubs will be planted within the project area
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Schedule
Public meeting to discuss 30% designs 2/11/2014Public meeting to discuss 30% designs 2/11/2014
60% design – Summer 2014
90% design Winter 201490% design – Winter 2014
Permits issued – Spring 2015
C t ti S Construction – Summer 2015
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Q ti /C t ?Questions/Comments?
Darian Copiz, Montgomery County Department of Environmental Protection240‐777‐7774 / [email protected]
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4 777 7774 / p @ g y y gwww.montgomerycountymd.gov/watershedrestoration
Click on “Stream Restoration” and “Stormwater Pond Retrofits”