Upper Broad Run Watershed Management Plan

Upper Broad Run Watershed

Management Plan

Nancy Roth, M.S., PMPAlexi Boado, M.S., M.P.A.

April 10, 2014 – Loudoun Valley Estates Clubhouse

Watershed Partnership WorkgroupMeeting #3

1

• Introductions

• Overview of watershed plan development process

• Field results – Retrofit reconnaissance

• Highlights of Interim Report • Pollutant loads and general strategies for load reductions

• Subwatershed-specific restoration strategies

• Comments

• Planning for Community Meeting

• Work in progress and next steps

Agenda

Overview of Watershed Plan Steps• Public Involvement

• Community meeting (September 2013), 1 more planned (May 2014)• Watershed Partnership Workgroup meetings, 2 to date (Oct. 2013,

Jan. 2014), 2 more (April and May 2014)• WRTAC presentation (Feb. 24, 2014)

• Development of vision, goals, and objectives• GIS investigations• Field investigations• Development of proposed watershed management actions

and strategies• Modeling pollutant loads and expected load reductions• Interim report• WPW review• Refine proposed actions and strategies• Model future land use and pollutant loads• Watershed plan report

Retrofit Reconnaissance of Existing Stormwater BMPs

• Seeking opportunities to enhance water quality treatment in existing stormwater infrastructure

• Current database of BMPs (94) reviewed to select best candidates for field investigation

• 28 small and/or “manufactured” BMPs• Small drainage = not cost effective to update

• 66 “ponds”• Large drainage areas = cost effective to update

• Types• 19 wet ponds• 46 “dry” ponds• 1 wetland

• Ownership• 35 County-owned• 28 privately-owned • 3 school-owned

• Screening for field visit • Type of pond (efficiency), date of construction, aerial

pictometry, conversations with County staff

• = 35 “ponds” field visited of 66• Budget limited

66 “Ponds”

Retrofit Reconnaissance of Existing Stormwater Ponds

Results of 35 Field Investigation

• 35 ponds yielded 44 possible options• Complete pond conversion or pre or post

treatment within “pond” boundary using bioswales/bioretention

• 12 high priority conversions, 14 medium, 16 low• 2 not upgradeable / state-of-the-art

• Poor soils (slow percolation) and flat topography made conversion to wet pond or wetlands most common recommendation (31)

• Not upgradeable / Modern multi-chamber design with wet pool• 20% nitrogen, 45% phosphorus, 60% sediment• One fault, it attracts Canada Geese

Claiborne & Zion Chapel Rd. (BC45)

(1) Existing flood control dry “pond” conversion to a wet pond or wetland (20% N, 45% P, 60% sediment)

(2) Pre-treat stormwater entering existing “pond” with dry swale (70%,75%,80%)

• Low pollutant removal value (5% nitrogen, 5% phosphorus, 10% sediment)• Few secondary ecological benefits• Aesthetic value?• Possible wet pond (20%,45%,60%)

Allison Ridge Terrace (AJ4280)

Rogerdale Place (GC554)

• Low pollutant removal value (5% nitrogen, 5% phosphorus, 10% sediment)• Few secondary ecological benefits• Aesthetic value?• Possible wet pond or wetland (20%,45%,60%)

• Pretreatment into existing pond using bioswales in existing grassed swales

• These opportunities are very uncommon within ponds• Existing swale treatment 0%,0%,0%?• Bioswale, 70% N, 75% P, 80% sediment

Loudoun Valley Estates(JC3947)

• Pretreatment into existing pond using bioswales in lieu of concrete swales

• This is not within pond area but may be within pond easement?

Gleedsville Manor (JC4162)

Interim Report on the Upper Broad Run Watershed Management Plan Pilot Project

• Chapter 1: Introduction • Chapter 2: Vision, Goals, and Objectives • Chapter 3: Desktop Assessment of Current

Conditions • Chapter 4: Field Assessment • Chapter 5: Stormwater Management and Other

Watershed Management Strategies • Chapter 6: Modeling • Chapter 7: Subwatershed Restoration Strategies• Chapter 8: Subwatershed Ranking

Based on 2012 land use

• Total Nitrogen: 231,000 lbs/year

• Total Phosphorus: 15,000 lbs/year

• Total Sediment: 3,298,000 lbs/year

Estimated Pollutant Loads from Upper Broad Run

Data from Interim Report, Chapter 6

Upper Broad Run: Sources of Nutrient and Sediment

34%

46%

20%

Nitrogen Loads

Urban

Agricultural

Forest/Wetlands/Water

30%

63%

7%

Phosphorus Loads

Urban

Agricultural


49%

43%

8%

Sediment Loads

Urban

Agricultural


2012 Land Use Scenario


Types of Proposed Urban/SuburbanStormwater Control Measures (SCMs)

• Urban nutrient management• Pond conversions:

• Conversion of dry detention ponds (DP) to extended detention dry ponds (ED DP)• Conversion of dry ponds to infiltration practices• Conversion of dry ponds to extended detention wet ponds / wetlands (ED WP)• Addition of pretreatment or post treatment SCMs within existing dry or wet pondboundaries

• New SCMs (retrofits) outside of existing dry or wet pond boundaries but which woulddrain into an existing pond or capture and treat stormwater just outside of the existingpond.• Reforestation

• Stream buffers• Upland areas

• Stream restoration for erosion control and nutrient processing• New Micro-SCMs (LID) such as bioretention, bioswales, urban filtration practices, etc.not associated with an existing dry or wet pond• Downspout disconnection• Impervious cover removal

Interim Report, Chapter 5

ErosionTable 4-21: Pollutant Removal Efficiencies of Select BMPs as Provided by VAST February 2014

Select BMPS from VAST**Nitrogen

Effectiveness (%)Phosphorus

Effectiveness (%) Sediment Effectiveness (%)

Urban Nutrient Management Plan Low Risk Lawn 6 3 0

Street Sweeping 25 times a year-acres 3 3 9

Urban Nutrient Management Plan 9 4.5 0

Vegetated Open Channels - C/D soils, no underdrain 10 10 50

Urban Nutrient Management Plan High Risk Lawn 20 10 0

Dry Detention Ponds and Hydrodynamic Structures 5 10 10

Permeable Pavement w/o Sand, Veg. - C/D soils, underdrain 10 20 55

Permeable Pavement w/ Sand, Veg. - C/D soils, underdrain 20 20 55

Dry Extended Detention Ponds 20 20 60

Wet Ponds and Wetlands 20 45 60

Vegetated Open Channels - A/B soils, no underdrain 45 45 70

Bioretention/raingardens - C/D soils, underdrain 25 45 55

Urban Forest Buffers 25 50 50

Permeable Pavement w/o Sand, Veg. - A/B soils, underdrain 45 50 70

Permeable Pavement w/ Sand, Veg. - A/B soils, underdrain 50 50 70

Urban Filtering Practices 40 60 80

Bioswale 70 75 80

Bioretention/raingardens - A/B soils, underdrain 70 75 80

Permeable Pavement w/o Sand, Veg. - A/B soils, no underdrain 75 80 85

Permeable Pavement w/ Sand, Veg. - A/B soils, no underdrain 80 80 85

Urban Infiltration Practices w/o Sand, Veg.-A/B soils, no underdrain 80 85 95

Urban Infiltration Practices w/ Sand, Veg. - A/B soils, no underdrain 85 85 95

Bioretention/raingardens - A/B soils, no underdrain 80 85 90

Restoration Strategies

Two categories:

County-led strategies - large capital projects

Citizen-based strategies - locally based programs

Partnership between County government, other agencies, citizens, businesses, and other organizations

Participation at all levels is critical for success

Photo credit: Rain Barrels of Annapolis

Two Implementation Scenarios

• Maximum Potential: All available units

• Projected: with expected participation rates

Reduction estimates based on available BMP removal efficiencies

Pollutant Removal Analysis


Pollutant Load ReductionsTable 6-28: Summary of Pollutant Load Reduction Estimates (TN, TP, and Sediment)

BMP How Credited

TN Efficiency

TP Efficiency

Sediment Efficiency

Max Potential TN Load Reduction (lbs/yr)

Max Potential TP Load Reduction (lbs/yr)

Max Potential Sediment Load Reduction (lbs/yr)

Units Available

Projected Participation (%)

Projected TN Load Reduction (lbs/yr)

Projected TP Load Reduction (lbs/yr)

Projected Sediment Load Reduction (lbs/yr)

Existing Stream Restoration Lbs per Ln Ft 0.2 0.068 54.25 100 34 27,125 500 ft 100 100 34 27,125

Existing SCMs Efficiency varies varies varies 4,209 522 232,961 2,047 acres 100 4,209 522 232,961

SCM Conversion Efficiency varies varies varies 1,843 242 196,554 48 acres 100 1,843 242 196,554

New SCMs (NSA, ISI, PAA, HSI) Efficiency varies varies varies 235 42 19,731 43 acres 50 117.7 21.04 9,866

Impervious Cover Removal (ISI) LU Conversion N/A N/A N/A 3.84 0.86 350 0.49 acres 50 1.92 0.43 175

Reforest Stream Buffer LU Conversion + Efficiency 25% 50% 50% 4,601 315 78,735 419 acres 65 2,991 205 51,178

Pervious Area Reforestation LU Conversion N/A N/A N/A 379 15 4,500 50 acres 50 190 7.43 2,250

New Stream Restoration lbs per Ln Ft 0.2 0.068 54.25 1,122 381 304,234 5,608 ft 75 841 286 228,176

Downspout Disconnection (NSA) Efficiency 50% 60% 90% 515 61 35,312 47 acres 33 170 20 11,653

Tree Plantings (NSA) LU Conversion N/A N/A N/A 394 15 4,668 52 acres 33 130 5 1,540

Tree Plantings (ISI) LU Conversion N/A N/A N/A 385 15 4,573 51 acres 66 254 9.96 3,018

Urban Nutrient Management Efficiency varies varies N/A 678 39 N/A 15 acres 100 678 39 N/A

Total 14,465 1,682 908,742 11,526 1,391 764,495

Total Existing Urban Load (lbs/yr) 79,126 4,503 1,579,710 79,126 4,503 1,579,710

Reduction Achieved 18.3% 37.4% 57.5% 14.6%

30.9% 48.4%


Reductions from Proposed Restoration Strategies


Subwatershed Strategies – ExampleExisting Conditions


Subwatershed Strategies – ExampleRecommendations


Subwatersheds – Overall Ranking


Work in Progress and Next Steps

• Refine Best Management Practice (BMP) options and restoration strategies

• Map – projected future land use and model future pollutant loads

• Continue coordination with Watershed Partnership Workgroup

• Community outreach meeting• Develop Implementation section• Prepare Watershed Plan report (draft, final)

Thanks again for your participation!

www.loudoun.gov/upperbroadrunwatershed

http://www.loudoun.gov/upperbroadrunwatershed

Upper Broad Run in Loudoun County

Upper Broad Run Watershed Management Plan

Documents

Transcript of Upper Broad Run Watershed Management Plan