Reusing Dredge Material on a Tidal Wetland

Alison Rogerson1, Andy Howard 1, Bart Wilson2

1 Delaware Department of Natural Resources and Environmental Control2 U.S. Fish and Wildlife Service

December 12, 2016

Project origin

• Delaware Wetland Conservation Strategy goal

• DNREC desire to find alternate uses

• Funded task under EPA wetland grant

• Goal:– Test the efficacy of restoring tidal wetland with dredge

material

– Investigate techniques, equipment, logistics, results

– Work towards developing a DNREC program

– Share as much information as possible

Project Site

Piney Point Tract of Assawoman Wildlife AreaDagsboro, DE

Background

- multi agency and partner project- tidal marsh restoration via thin layer application of dredge material-raise elevation to 1.05’ NAVD88- supply sediment and boost surface elevation-22 acres-10,000yd³

Upland Disposal

Aerial Application

Sediment sills: straw bales and waddles

Demonstration:February 25- March 25, 2013

Continuation:September 9-December 21, 2013

Southwest (SW)

Southeast (SE)

RTN Survey transects

elevation goal was 1.05 ft

Plant Regrowth

Biomass and Bearing Capacity

0

1

2

3

4

5

6

7

8

9

10

275

325

375

425

475

525

575

2012 2013 2014 2015B

ear

ing

Cap

acit

y

Bio

mas

s (g

)

Year

DemonstrationBiomass SW

ContinuationBiomass SE

DemostrationBearing SW

ContinuationBearing SE

2016

Feldspar marker horizons

Plot 1

Plot 4

Feldspar marker horizons

0

20

40

60

80

100

120

140

160

180

200

Mat

eri

al T

hic

kne

ss (

mm

)

Plot 1 Demonstration Plot 2 Demonstration Plot 3 Demonstration

Plot 4 Continuation Plot 5 Continuation

Lessons Learned:

• Site specific conditions will vary greatly!

• Aerially broadcasting material is possible

• Spray distance is limited by debris and wind

• Difficult to measure precisely how much is being applied

• Limit sediment to 10-15 cm

• Do not apply before heavy freeze

• Vegetation prevents major sediment runoff

• More feldspar plots

• Monitor mussels

Thanks for listening!

Alison Rogerson

Wetland Monitoring and Assessment Program

DNREC

alison.rogerson@state.de.us

302-739-9939

Cryogenic coring for feldspar horizon markers

measuring accretion thickness and surface movement