LANDSATAug 31, 2011

Sediment transport and deposition:salinity fronts and storm eventsDavid Ralston, Rocky Geyer,John Warner, Gary Wall

Hudson River Science SymposiumSUNY New Paltz – April 24, 2013

ETM

RiverOcean

Marinesediment

Fluvialsediment

deposition

Estuaries efficiently trap sediment

30 psu15 psu

1 psu

High sediment concentrations and deposition rates, efficient trapping

How does the Hudson compare with this cartoon?

stratified unstratified

estuarine circulation seaward flow

Hudson River estuary

Poughkeepsie

Haverstraw Bay

Tappan Zee

GW Bridge

Battery

120 km

60 km

45 km

18 km

0 kmHi

gh Q

r

Salin

ity in

trusio

n at

low

Q rAverage sediment input ~0.5 Mtons/yr

Newburgh Bay

95 km

NYC

AtlanticOcean

Lower Hudson ETM: near GW Bridge high deposition rates

June 1998

0 50 cm Woodruff et al. 2001

June 1999

AtlanticOcean

Geyer et al. 2001

Lower Hudson ETM: near GW Bridge high deposition rates high sediment concentrations (>1 g/L)BUT, at intermediate salinities, not at salinity limit

NYC

AtlanticOcean

Nitsche et al., 2010

Upper Hudson ETM? Haverstraw BayHigh deposition rates in Haverstraw;frequent dredging

Upper Hudson ETM: Haverstraw Bay

Ralston et al., 2012

Suspended sediment concentration

Salinity

High sediment concentrations observed at flood tide salinity fronts

Salinity intrusion

bottom salinityN S N S N S N S N S

Advances during neap tides, retreats during spring tides

Dist

ance

from

Bat

tery

(km

)

model results, Fall 2009

Frontal locations distributed along the estuary

bottom salinity gradient (s/x)

At constrictions: salinity gradient intensified and persistent

model results, Fall 2009

Piermont

GW Bridge

Croton Pt.

West PointDi

stan

ce fr

om B

atte

ry (k

m)

Salinity + bathy

bottom stress + sal.

SSC + velocityerosion/deposition + sal.

Net over 1 tidal cycleSlack before flood

Salinity front sediment trapping: Haverstraw Bay

model results, Fall 2009

Slack before flood Net over 1 tidal cycle

salinity + bathy

stress + sal.

SSC + velocity

erosion/deposition + sal.

Salinity front sediment trapping: GW Bridge

model results, Fall 2009

Tropical Storms Irene and Lee

Mohawk River @ Cohoes 8/29/11, 2.2 g/L (G. Wall)

Extremely high discharge: introduce new sediment, push salt seaward added almost 3 Mton of new sediment to the Hudson where did it go?

Tropical Storms Irene and Lee: discharge and sediment flux net sediment flux past Poughkeepsie only ~ 1/3 total input model consistent with observed fluxes data from USGS & HRECOS

3-2riversediment ~ QQ

Where did the new sediment go?

Mass distributions along the Hudson through time

Tropical Storms Irene and Lee

Irene start

Irene end

model results

Where did the new sediment go?

Mass distributions along the Hudson through time

Tropical Storms Irene and Lee

Before Lee

After Lee

model results

Where did the new sediment go?

Mass distributions along the Hudson through time

Tropical Storms Irene and Lee

1 mo. after Lee

model results

New sediment largely in the tidal river

Sediment in estuary remobilized by increased velocities & reduced stratification

Irene and LeeSuspended sediment

model results

New sediment deposition

1 month after Tropical Storm Lee

Bed sediment erosion & deposition

model results

Summary- Salinity fronts at topographic transitions trap sediment at multiple locations in estuary

- Sediment loading from extreme events greatly exceeds near-term transport capacity, with trapping in both tidal river and estuaryWhat’s next? Transport and trapping processes in tidal river not well documented or understood

Extreme events remobilize bed sediments in estuary, potentially with contaminants that had been sequestered

Sediment residence times may be much longer than thought, limiting export of carbon and other terrigenous material to the ocean