Managing the Watershed- Reducing Nutrients in Stormwater Runoff

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Managing the Watershed- Reducing Nutrients in

Stormwater Runoff

Buzzards Bay CoalitionDecision-Makers Workshop Series

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

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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

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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

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Watershed Boundaries

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Cape Cod Watersheds

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Stormwater/Watershed basicsUrbanization results in

increased surface runoff

BEFORE AFTER

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Components of Impervious Cover in the Urban Landscape

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Stormwater/Watershed basics

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

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8-10%8-10%

20%20%

30%30%> 65%> 65%

< 5%< 5%

Stormwater/Watershed basics

% impervious

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Community Planning

LID Site Design

LID/GI BMPs

Large Conventional BMPs

Receiving Waters

Stormwater Evolution LID/GI

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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

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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)

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Low Impact Development (LID)

Site Design

Traditional LID/GI

BMPs

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LID/GI Practice Library: Bioretention

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LID/GI Practice Library: Bioretention

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LID/GI Practice Library: Rain gardens

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LID/GI Practice Library: Porous Pavement/pavers

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LID/GI Practice Library: Infiltration

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LID/GI Practice Library: Green/blue roofs

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LID/GI Practice Library: Swales

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LID/GI Practice Library: Sand Filters

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LID/GI Practice Library: Gravel wetlands

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LID/GI Practice Library: Hydrodynamic separators

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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.)

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Pollutant Removal Capability

Source: 2010 Rhode Island Stormwater Design and Installation Standards Manual

WVTS = wet vegetative treatment system = constructed wetland

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Pollutant Removal (continued)

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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

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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

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Roger Williams Park Ponds

Watershed Areas

North Watershed

South Watershed

Watershed AreasNorth—977 acresSouth—649 acres

Total—1,626 acres 50% Impervious

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Roger Williams ParkPond System

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The Ponds Are Part of the Park’s

Historic Design and Character

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The Roger Williams Park Ponds are in trouble

today

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Rooted Aquatics

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Shallow Ponds, generally less than six feet

deep

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Lots of Resident Geese

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Sedimentation

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Invasive Species

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Upper Watershed

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Upper Watershed

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Upper Watershed

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* 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

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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

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Proposed Proposed Structural and Structural and

Non-Non-Structural Structural

SitesSites

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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.

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Name this activity?

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

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Site 3B – BioretentionDesign Plan

Diversion inlet/channel

Forebay

BioretentionPlanting Bed

Overflow/outlet

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Site 3B – Bioretention Installation

and Training Workshop (day 1)

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Site 3B – Bioretention Installation

and Training Workshop (day 2)

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Site 3B – Nearly Complete

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Slope Stabilization and Slope Stabilization and Buffer PlantingBuffer Planting

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Geese Management(not necessarily

a popular activity)

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Inflow Pipe from Upper Watershed

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In-pipe or In-lake Management?

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Educational Banners/Signage

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Rhode Island Salt PondsWatershed Restoration Plan

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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

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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

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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

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Stormwater Management Design Objectives

• Runoff Reduction • Groundwater Recharge• Water Quality Mitigation

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Wastewater Treatment Alternatives

• Decentralized Treatment - Onsite Individual Dwellings

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

• Porous de-nitrification media

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Other Pollutant Sources:

• Waterfowl (Canadian Geese and Mute Swans);

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

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