Managing the Watershed- Reducing Nutrients in Stormwater Runoff

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Managing the Watershed- Reducing Nutrients in

Stormwater Runoff

Buzzards Bay CoalitionDecision-Makers Workshop Series

UMass Cranberry Station, E. Wareham, MAMarch 20, 2013


Today’s Agenda

• The basics of stormwater and watershed management

• The evolution of stormwater management towards Low Impact Development(LID)/ Green Infrastructure (GI)

• 2 Examples of watershed planning efforts geared towards nutrient reduction


Stormwater/Watershed basics

http://planetearth.nerc.ac.uk/features/story.aspx?id=668

Watershed Hydrology What is a watershed?A: a building for water storage

B: the land area that drains to a given water body

C: a shack from which fishing occurs

D: a moment in time when you cross into a new area

E: a new way of organizing environmental agencies


Watershed Boundaries


Cape Cod Watersheds


Stormwater/Watershed basicsUrbanization results in

increased surface runoff

BEFORE AFTER


Components of Impervious Cover in the Urban Landscape



At ~10% impervious we begin to see: •Water quality issues•Impacts to biological communities•Increased flooding•Stream erosion•Loss of recreational uses•Shellfish bed closures•Reduced baseflow and recharge


8-10%8-10%

20%20%

30%30%> 65%> 65%

< 5%< 5%


% impervious


Community Planning

LID Site Design

LID/GI BMPs

Large Conventional BMPs

Receiving Waters

Stormwater Evolution LID/GI


Traditional controls

• Goal: Get the water out of here as fast as possible

• Collect and storage in big, “hole in ground” off-site

• Pipe discharge to a stream or wetland

• Limited water quality treatment and infiltration

• Stormwater is a waste product

LID/GI controls• Goal: Reduce the amount of

surface runoff by reducing impervious cover and preserving natural areas

• Rely on small, distributed on-site practices

• Infiltrate or reuse as much as possible; filter before discharge

• Source controls to minimize pollution

• Stormwater is a resource

Stormwater Evolution LID/GI


Time (hrs)

Ru

nof

f (c

fs)

Post-development

Pre-development

Adapted from David Nyman, ENSR

Runoff Hydrograph

Stormwater basics

Post-development (with traditional controls)

Post-development (with LID/GI)


Low Impact Development (LID)

Site Design

Traditional LID/GI

BMPs


LID/GI Practice Library: Bioretention


LID/GI Practice Library: Rain gardens


LID/GI Practice Library: Porous Pavement/pavers


LID/GI Practice Library: Infiltration


LID/GI Practice Library: Green/blue roofs


LID/GI Practice Library: Swales


LID/GI Practice Library: Sand Filters


LID/GI Practice Library: Gravel wetlands


LID/GI Practice Library: Hydrodynamic separators


LID Practice Library: Others

• Downspout disconnection

• Pervious area restoration/soil amendments

• Urban reforestation• Municipal pollution

source control (street sweeping, catch basin cleaning, leaf litter pick-up, etc.)


Pollutant Removal Capability

Source: 2010 Rhode Island Stormwater Design and Installation Standards Manual

WVTS = wet vegetative treatment system = constructed wetland


Pollutant Removal (continued)


LID/GI Runoff Reduction Potential

Practice: Runoff ReductionPonds and Wetlands none to lowInfiltration highestBioretention moderate to highSwales moderate to highPorous Pavements highGreen Roofs moderateHydro-Separators none


Roger Williams Park, Providence, RI

• Largest & Most Important Open Space in Providence

• 435 Acres• 100+ Acres of Ponds• 1 Million visitors per

year• Horace Cleveland

(Olmstead School), 1874


Roger Williams Park Ponds

Watershed Areas

North Watershed

South Watershed

Watershed AreasNorth—977 acresSouth—649 acres

Total—1,626 acres 50% Impervious


Roger Williams ParkPond System


The Ponds Are Part of the Park’s

Historic Design and Character


The Roger Williams Park Ponds are in trouble

today


Rooted Aquatics


Shallow Ponds, generally less than six feet

deep


Lots of Resident Geese


Sedimentation


Invasive Species


Upper Watershed


* Some Uncertainty Here

Total: 906 lbs/year

Preliminary Estimates of Annual Phosphorus LoadsComing into the Roger Williams Park Ponds (lbs/year)

~70% Reduction required by TMDL


Watershed Management Plan Implementation

Recommendations• Structural Best Management Practices;• Non-structural measures (pavement

removal/shoreline vegetation);• Geese population management• In-pond treatment (water column,

sediment);• Education and Outreach;• Water quality monitoring; and• Upper Watershed recommendations


Proposed Proposed Structural and Structural and

Non-Non-Structural Structural

SitesSites


Rapid Retrofit Reconnaissance (RRR)

• Covered both Upper and Lower Watersheds

• Assessed potential retrofits, shoreline restoration/slope stabilization sites, neighborhoods, hotspots, maintenance needs, and overall watershed boundaries

• GIS maps, various existing design plans, manhole poppers, measuring tapes, etc.


Name this activity?


Site 3B – Carousel Parking Lot Bioretention (concept plan)


Site 3B – BioretentionDesign Plan

Diversion inlet/channel

Forebay

BioretentionPlanting Bed

Overflow/outlet


Site 3B – Bioretention Installation

and Training Workshop (day 1)


Site 3B – Bioretention Installation

and Training Workshop (day 2)


Site 3B – Nearly Complete


Slope Stabilization and Slope Stabilization and Buffer PlantingBuffer Planting


Geese Management(not necessarily

a popular activity)


Inflow Pipe from Upper Watershed


In-pipe or In-lake Management?


Educational Banners/Signage


Rhode Island Salt PondsWatershed Restoration Plan


Scope of Project• Watershed Assessment

– Stormwater management inventory– Existing wastewater management

programs/policies– Alternative wastewater technologies,

disposal & funding options• Watershed Management Plan

– Stormwater/Wastewater Management Options– Outreach and education plan– Specific Implementation plan– Monitoring plan


Nitrogen Thresholds and Water Quality Classification

Classification Nitrogen (mg/L)

Excellent Quality <0.30Good Quality 0.3 - 0.39Moderate Impairment 0.39 - 0.50Significant Impairment 0.50 - 0.70Severely Degraded >0.70


Total Loading and target TN Reduction:

Ninigret Pond: 71,237 #/year: Reduction needed = 0 #/yr

Green Hill Pond: 57,805 #/year: Reduction needed = 39,978 #/yr


Stormwater Management Design Objectives

• Runoff Reduction • Groundwater Recharge• Water Quality Mitigation


Wastewater Treatment Alternatives

• Decentralized Treatment - Onsite Individual Dwellings

• Centralized Treatment/Small Scale/Cluster (multi-home) Treatment

• Porous de-nitrification media


Other Pollutant Sources:

• Waterfowl (Canadian Geese and Mute Swans);

• Other wildlife;• Pets;• Fertilizer from lawns/gardens;• Some agricultural loading; and• Atmospheric deposition.

Managing the Watershed- Reducing Nutrients in Stormwater Runoff

Education

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