View
240
Download
1
Category
Tags:
Preview:
Citation preview
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
Recommended