Groundwater-Surface Water Interactions

• Groundwater and surface water are intertwined• Different types of interactions of groundwater with:

– streams and rivers– lakes– wetlands– oceans

• Focus on groundwater-stream interactions– gaining vs losing– measurements– role of hyporheic zone

Groundwater-Stream Interactions

Gaining reach

Losing reach

Groundwater can discharge to streams (gaining stream) or streams can discharge to groundwater (losing stream).

Gaining and losing reaches can occur along the same stream (see example above)

Fetter, 2000

Determine gaining/losing stream via equipotentials

Gaining Stream:convex equipotential lineszones of groundwater dischargenet increase in flow

Losing Stream:concave equipotential lines zones of groundwater rechargenet loss of flow

Freeze and Cheery (1979)

Hyporheic Zone: region between groundwater and surface water

ground water

active channel

floodplain

hillslope

riparian

hyporheic zone

Defined as the portion of the groundwater interface in streams where mixture of surface and groundwater is found.

Occurs beneath the active channel and within the riparian zone

Key Components of the Hyporheic Zone

interface of groundwater and channel water

associated gradients in biogeochemical variables (pH, redox, microbial populations, organic content, light, temperature)

Hyporheic zone: ground water habitat of stream ecosystems

Stygobromus: subterranean amphipod

hyporheic mayfly

Original use by Orghidan (1959) as groundwater environment with distinctive biota

Hyporheic zone metabolically active, impacts nutrient cycling, which impacts stream ecology

Upwelling waters bring groundwater nutrients to stream channel

Controls on upwelling vs. downwelling

Streambed morphology

Vertical Gradients

Dahm and Valett, 1996

dhdL

= ' - '

= ' + 'dh

Downwelling

Upwelling

Vertical Hydraulic Gradients measured using piezometers or manometers

dL

dh

dL

dhfree water surface

dL

Temporal variations in gradients can be significantV

HG

(c

m/c

m)

from Valett (1993)

Influence of ET Influence of Floods

Time (days) 1 2 3 4 5 6 7 8 9

hea

d (m

)0.1

0.2

0.3

0.4

downwelling

0.8m belowstream bed

streamupwelling

after Lee and Hynes (1977)

Groundwater-stream interactions exert control on solute cycling, biota, and stream hydrology

Can be better understood through:• delineating gaining (upwelling) and losing (downwelling)

reaches through measuring vertical gradients• quantifying the upwelling or downwelling discharge (Q)

using stream gauging methods• mass balance methods to assess the role of the

hyporheic zone in impacting solute transformation, retention and/or release

Challenge: spatial and temporal variability may be significant!

Case Study 1: Hyporheic influences on Sycamore Creek, AZ (Valett et al., 1994)

upstream algal communities (750 mg/m2 as

Chl a) dominated by green algae

100 m downstream algal communities (98 mg/m2 as Chl a) dominated by bluegreen bacteria

Flash flooding represents a disturbance thatreduces Chl to belowdetection limit and kills 95-99% of allinvertebrate fauna

From Valett et al. (1994)

Patterns of GW/SW Exchange: Sycamore Creek

From Valett et al. (1994)

VHG: 0.1 - 0.7 VHG: ~ 0 VHG: 0 to -1

Dry Stream Bed

after Valett et al. (1994)From Valett et al. (1994)

GW/SW Exchange and Ecosystem Resilience

after Valett et al. (1994)From Valett et al. (1994)

Case Study 2: Groundwater-stream interactions in a mine setting

º

0 0.5 1 Km

" BAMS

Virginia

Tailing piles

Arsenopyrite-bearing schist

Produced As2O3 1903-1919

Brinton Arsenic Mine

Lottig, 2005Watson, 1911

Mine

Foundation

Waste

piles

50 m

N

Waste piles resulting from mining operations lie adjacent to a headwater stream

Streamflow

Start

End

Schreiber, unpublished

Waste pile

stream

stream

Gaining stream

Groundwater contributes high concentrations of As to stream

Schreiber, unpublished

gwgwgw QAsLgross

*][

Is there any retention of arsenic in the HZ as groundwater discharges to the surface?

Gross groundwater load

Groundwater arsenic concentration

Groundwater discharge

Hyporheic zone

Stream

grossgwL[As]

[As]

Use a mass-balance approach. First, find the gross groundwater load

.

B. Brown, unpublished

Now, find the net groundwater load: the difference between loads entering and leaving the study reach

updwngw LLLnet

Net groundwater load

Load entering the study reach

Load leaving the study reach

Hyporheic zone

Stream

upL

netgwL

dwnL B. Brown, unpublished

Now, calculate retention: the difference between the gross and net groundwater loads

netgross gwgwHZ LLR

If RHZ = negative,=> net release in HZ

If RHZ = positive,=> net retention in HZ

Hyporheic zone

Stream

netgwL

grossgwL

B. Brown, unpublished

Using the mass-balance method, whole reach retention of As can be calculated

Process:

(1) Delineation of hyporheic zone

(2) Establishment of the spatial variability of groundwater discharge

(3) Characterization of groundwater flowpaths

(4) Preliminary assessment of subsurface arsenic concentrations

Stream

B. Brown, unpublished