Lake Seminole Restoration Dredging Presented by Rob Burnes MS, MAS - - PowerPoint PPT Presentation

Lake Seminole Restoration Dredging

Presented by Rob Burnes MS, MAS Senior Environmental Scientist Pinellas County Public Works

Background

▪ 684 acres ▪ 5.5 feet average depth ▪ Control structures regulate lake

level

▪ Primarily used for recreation ▪ Fish community dominated by

sunfish family

▪ Healthy emergent and

submerged vegetation communities

Lake Seminole History-1940’s

▪ Tidal estuarine system

▪

Mangroves

▪

Salt marshes

▪ Lake created in late-1940’s

▪

Irrigation for orange groves

▪

Potable water source

▪ Impounded an arm of Long

Bayou

▪ Flooded the system with

freshwater from Long Creek

Lake Seminole History-1950’s & 1960’s

▪ Rapid expansion in the

area surrounding the lake

▪ Start of decline in

ecological conditions

▪ Lake Seminole Park

Constructed

▪ Current semi-circular weir

installed in late 1960’s

Lake Seminole History-1970’s & 1980’s

▪

Land use Switch

▪

1976 Lake Seminole Bypass Canal created

▪

By the mid to late 1980’s

▪

Water quality was at an all-time low

▪

Nuisance vegetation at an all time high

▪

1989 Pinellas BOCC passes resolution of long-term management plan

Lake Seminole History-1990’s to Present

▪ Built out watershed ▪ Poor water quality

▪

Habitat loss

▪

Decline of sport fishery

▪

Harmful algal blooms

▪ Restoration efforts kick into

high gear

▪ Watershed management

plan finalized in 2001

Lake Seminole Restoration Efforts

1971- Elimination of direct input from wastewater plant 1987- Grass Carp introduced 1990’s- Stormwater pond rehabilitations 2001- Lake Seminole WMP 2002- Littoral shelf sediment removal and revegetation 2006- Lake draw-down and nuisance vegetation removal, replanting, and drainage improvements 2007- Lake Seminole Reasonable Assurance Plan adopted 2010’s- Construction of alum stormwater treatment systems

Reasonable Assurance Plan

▪ Developed in response to

being an impaired waterbody pursuant to section 303(d) of the federal Clean Water Act

▪ Plan finalized in 2007, updated

every 4 years

▪ Defined Structural,

Management, Legal, and Policy Components

Organic Sediment Dredging

▪

Number one recommended project in Reasonable Assurance Plan

▪

Removal of 900,000 cubic yards

• f organic sediments

▪

Result in removal of ▪

416 tons of TN

▪

77 tons of TP

▪

Goal is to reduce lake’s internal nutrient loads

In-Lake Dredging Timeline

▪ Dredge Material Management

Area (DMMA) construction started in January 2019

▪ Active dredging to began in

December 2019

▪ Dredging to be completed by

2021

Hydraulic Dredging-How it Works

▪ Dredge barge moved

into place by tender vessels

▪ Dredge template loaded

• nto barge GIS system

▪ Cutter head of barge

will loosen muck and vacuum will suck up sediment

Hydraulic Dredging-How it Works

▪ Sediment then sent by pipe

to upland dewatering site

▪ Slurry in the pipe

approximately 5-8% solids

▪ Sediment and associate

debris separated at upland site

▪ Clean sediment-free water

returned to the lake

Dredge Material Management Area

Example

▪

Area where dredged sediment will be placed.

▪

At the end of the project area will be capped with sand and sodded

▪

Pinellas County Parks will take over for use as recreational fields

Dredge Material Management Area

▪

21 Acres at the top

▪

50’ Deep

▪

Will contain approx. 800,000 CY during

• peration

Why this Approach

▪

Positive long-term environmental benefits (water quality, fisheries, beneficial habitats)

▪

Increases recreational opportunities

▪

Expanded youth sports in the unincorporated Seminole area

▪

Expand upland recreational opportunities

▪

Reduces traffic and impacts on schools and residents on 98th St.

▪

Reduces project cost by nearly $20 million dollars

The Good News-Recent Water Quality

▪ Time series analysis

shows significant decreasing trends

▪

Chl-a (Both Lobes)

▪

TP (Both Lobes)

▪

TN (Both Lobes)

▪

Turbidity (Both Lobes)

▪

TSS (Both Lobes)

Next Steps in Restoration

▪ Allow the DMMA site to settle and consolidate

for at least one year prior to capping

▪ Continue monitoring

▪ Surface water ▪ Groundwater wells around the DMMA ▪ Groundwater seepage into the lake

▪ Plant trees to offset removal from DMMA site ▪ Wetland restoration near DMMA site

SWFWMD Project Video

For additional project information and updates:

▪ Visit the project website at

www.pinellascounty.org/lake_Seminole_restoration.htm

• r

www.pinellascounty.org/environment/watershed/watershed- lake-seminole.htm

▪ Contact the Project Manager

Rob Burnes Public Works Environmental Management 22211 US Hwy 19 N Bldg 10, Clearwater, FL 33765 Phone (727) 453-3149 Email rburnes@pinellascounty.org

www.pinellascounty.org/publicworks

Special Thanks to our Funding Partners