This document outlines a study to assess the effectiveness of a regional stormwater facility in Sarasota County, Florida, designed to treat stormwater runoff from over 55 square miles. It describes the methods for hydrologic and water quality monitoring over a 24-month period, including sampling during storm events and baseflow conditions. The data collected will inform future improvements in stormwater management practices and BMP designs to enhance water quality.

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Abstract
Contact information
Quantifying the Effectiveness of Stormwater BMPs Through
Hydrologic and Water Quality Monitoring
Rob Mooney, Hydrologic Data Collection; John Coffin, Hydrologic Data Collection;
Gary Serviss, Vanasse Hangen Brustlin, Inc.
This poster gives an overview of a planned study to measure the
effectiveness of a Regional Stormwater Facility (RSF) in the
treatment of stormwater runoff.
The RSF is designed to treat more than 55 square miles (3,583
acres) of the Phillippi Creek Watershed in Sarasota County, Florida.
The treatment Best Management Practices (BMPs) consist of a
series of four cascading wet detention ponds and a large wet
retention/wetland area. The southern portion of the project is a 30-
acre wet detention pond that will also serve to treat and re-route
water into the RSF during high flow periods. The wet detention
system includes treatment cells planted with a variety of emergent
wetland plants.
The site will also serve as a passive recreational use facility where
educational displays about stormwater treatment and flood control
will be constructed.
HDC and VHB will conduct continuous hydrologic (stage and
discharge) monitoring at multiple locations over a 24-month period
as well as a time of travel study. Flow-weighted storm event and
baseflow sampling will also be conducted using refrigerated
samplers at two inflow, two internal and three outflow stations
during seven to ten storm and baseflow events. In situ water quality
monitoring will be conducted concurrent to sampling events.
Samples will be analyzed by the County’s laboratory for ammonia
nitrogen, NOx nitrogen, TKN, organic nitrogen, total nitrogen,
orthophosphorus, total phosphorus, total suspended solids and
BOD. VHB will review the data, conduct the BMP effectiveness
evaluation and produce the final report. The study will help to
improve future estimates for nutrient load reductions and improve
future management decisions and BMP designs.
Methodology, Site Map and Site Photos Data Examples
Summary
Contact information
Hydrologic Data Collection
805 Vassar Road
Alexandria, VA 22314
Rob Mooney
Vice President
202-341-9811
Rob.Mooney@hydrologicdata.com
Vanasse Hangen Brustlin, Inc.
8043 Cooper Creek Boulevard, Suite 201
University Park, FL 34201
Gary M. Serviss, LEED AP
Principal Scientist
941-351-8986
gserviss@vhb.com
Water quality, discharge, and rainfall will be monitored and recorded on a continual basis over a 24-month period.
Stage and Discharge Measurements
Discharge will be measured at two inflow locations, at the inflow and
outflow of the South Cell, and at the three outflow locations from the
site using pressure transducers and velocity meters. Stage vs.
discharge ratings will be developed by making discharge
measurements using the standard USGS mid-section method using
Price AA, Pygmy or Acoustic Velocity Meters. Discharge will be
computed at 15-minute increments by developing standard stage vs.
discharge ratings for pressure transducers, and point velocity vs. index
velocity and stage vs. area ratings for the velocity meters.
Water Quality: In Situ Monitoring
In situ water quality measurements (temperature, pH, conductivity,
dissolved oxygen, and turbidity) will be collected concurrent with
automatic sampler sample collection using a multi-parameter sonde.
The water quality measurements will be approximately mid-stream
near the bottom of the water column.
Water Quality Samples: Stormwater Sampling
Water quality samples will be collected on a flow-weighted basis at
the two inflow sites, at the inflow to the South Cell, at the inflow to the
Walker Tract and at the three outflow sites during rain events by
using automated refrigerated samplers. Unless there are drought
conditions, it is anticipated that water quality data for seven to ten
storms would be collected. In addition to storm event sampling, seven
to ten samples of baseflow will be taken to determine the
effectiveness of the BMP under these conditions. The water quality
data will provide the basis for calculating the efficiency of the system
in reducing pollutants. The water quality samples will be delivered to
a certified laboratory who will analyze water quality samples using
standard EPA methods.
This project outlines an approach to hydrologic and water quality
monitoring that can be used to document the effectiveness of newly
constructed stormwater BMPs. Collection of data during baseflow
and storm events can be used to determine the impact of various
designs on the reduction of stormwater volume, nutrient loads and
sediment transport.
Billions of dollars are being spent nationwide on BMP construction
and stream restoration projects to mitigate the effects of stormwater
on water quality. Setting up monitoring networks on these projects
provides critical information that can be used for multiple purposes,
such as:
• Improving future estimates of nutrient load reductions for use
in models and watershed planning.
• Improving future BMP and stream restoration designs based
on real-world data.
• Demonstrating quantifiable project results to taxpayers.
• Improving future watershed management decisions.
Examples of Overall BMP Pollutant Removal Efficiencies
(Final report will detail overall removal efficiencies as well as individual section efficiencies of the monitored
BMP for all parameters, under both storm and baseflow conditions, in dry and wet seasons).
Aerial photo of the Celery Fields Regional Stormwater Facility.
Water flows through the facility from North to South.
VHB and HDC staff select monitoring locations at the Central Cell
overflow culvert of the Celery Fields RSF.
Weatherproof equipment shelter at wet detention pond with
continuous stage and water quality monitoring instruments,
refrigerated sampler, and telemetry.
Equipment installation at Central Cell outflow culvert (Site 4) will
include continuous stage and water quality monitors, a refrigerated
sampler and telemetry system.
Total Phosphorus Load Duration Curve
0.0
0.1
1.0
10.0
100.0
1000.0
10000.0
0 10 20 30 40 50 60 70 80 90 100
Percent of Days Flow Equaled or Exceeded (%)
MeanDailyStreamflow(cfs)
Higher Loads Lower Loads
Discharge of 36.4 cfs is equalled
or exceeded 60% of the time
Black Line - flow duration curve for the station's period of record
Red line - load duration curve for the parameter standard
Blue line - load duration curve allowing for a 10% safe margin
▲ - Water quality samples as loads plotted using the flow duration
at which they were sampled.
Points above the curve represent exceedance
of standards and allowable loadings