Salinity Intrusion: Integrating Riverine and Coastal Forces

Paul Conrads U. S. Geological Survey SC Water Science Center

Columbia, SC

NIDIS Carolinas Pilot Project Scoping WorkshopJuly 31, 2012

Outline Conceptual model of salinity

intrusion Look at some data Drought and salinity intrusion Coastal drought index and data

resource Summary

Short Review Salinity DynamicsFreshwater

SaltwaterRiverine

FlowTidal Forcing mean water level, tidal range

“…estuaries may never really be steady-state systems; they may be trying to reach a balance they never achieve.”

Keith Dyer, from Estuaries – A Physical Introduction (1997)

Saltwater-Freshwater Interface

High flowsLow water

levels

Tidal MarshesCritter Communities

Saltwater-Freshwater Interface

Low flowsHigh water

levels

Tidal MarshesCritter Communities

Example of Data: Yadkin-Pee Dee Basin

FreshwaterSaltwater

Riverine Flow

Tidal Forcing mean water level, tidal range

Flow: Pee Dee River at Pee Dee

Water level and Tidal Range: Atlantic Intracoastal Waterway at Little River Inlet

Specific conductance (salinity): Waccamaw River the Hagley Landing

Example of Data: StreamflowFreshwater

SaltwaterRiverine

FlowTidal Forcing mean water level, tidal range

Example of Data: Water levelFreshwater

SaltwaterRiverine

FlowTidal Forcing mean water level, tidal range

Two signals:Mean water level & Tidal Range

Tide Range

Mean Water Level

Water Level and Tidal Range

Pee Dee River Flows

Waccamaw River Specific Conductance

Flows and Specific Conductance

SPEC

IFIC

CO

ND

UC

TAN

CE,

UG

/CM

and

FLO

W, F

T3 /S

GA

GE

HEI

GH

TS A

ND

FIL

TER

ED G

AG

ES H

EIG

HT,

FEE

T

Converging Conditions

Looking Inside the Black Box

3D response surfaces Surface created by

model “Unseen” variables

set to constant value

Manifestation of historical behavior of system

Insight to the process dynamics or physics

What Conditions Cause Large Intrusions?

High water

Low water

3-D Response surface – Flow, Tidal Range, and Salinity

Sal

inity

>

Sal

inity

>

Flow >

Flow > Tide range >

Tide range >

Low Coastal Water Level High Coastal Water Level

Savannah River

Riverine Flows

Savannah River at Clyo

Tidal ForcingMean Water levelTidal Range

Fort Pulaski

FreshwaterSaltwater

Specific conductance

I-95

Savannah River at I-95

Converging Conditions:Savannah River

Flow and Drought Index

Very quick look at South Carolina Coast

Weekly drought index for Marion County

Plot with 7-day average flow & 7-day average specific conductance

Flow and Drought IndexD4

D3

D2

D1

0-D0

Specific Conductance and Drought Index

D4

D3

D2

D1

0-D0

Data Resource – USGS Real-time Network

USGS Coastal Carolina Real-time Network~50 active gages:

Parameters: water level, sp. cond., temperature, dissolved oxygen, turbidity, pH, and/velocity

Summary Salinity dynamics results of flow and

coastal water interaction Salinity intrusion events caused by

convergence of conditions Potential of a salinity coastal drought

index Real-time data networks available to

support potential coastal drought index

Paul ConradsUSGS South Carolina Science Center

pconrads@usgs.gov

Fast Forward

FERC Re-licensing

AIW/North End Salinity

Example of Data: StreamflowFreshwater

SaltwaterRiverine

FlowTidal Forcing water level, tidal range

Convergence of Conditions

Orbital Mechanics and Tide Range

Neap Tides Spring Tides

Tidal Range and Specific Conductance

Water Level and Specific Conductance

Converging Conditions:South End – Waccamaw River