Surface and Ground Water Mixing in a Karst Aquifer: An Example From the Santa Fe River

1
Surface and Ground Water Mixing in a Karst
Aquifer An Example From the Santa Fe
River

• Randy Dean

Department of Geological Sciences University of
Florida
2
Surface and Ground Water Mixing in a Karst
Aquifer

• Introduction
• Tracing the Subsurface Flow of the Santa Fe River
• Surface and Ground Water Mixing
• Conclusions/Whats Next

3
Introduction

• Vulnerability of Karst Aquifers
• Importance of Karst Aquifers
• Variations of Spring Discharge
• Physical and chemical changes
• Linked systems

4
Objectives

• Determine surface and ground water mixing in a
  karst aquifer
• Determine extent of fluid-solid reactions
  resulting from mixing

5
Specific Questions

• 1) Does injection of surface water influence flow
  through and chemical reactions within a karst
  aquifer?
• 2) Subsurface flow rates vs. river discharge
  rates?
• 3) Does mixing proportion of surface water and
  ground water vary?

6
Study Area
Hamilton
Madison
Jefferson
Suwannee River
Columbia
Baker
Suwannee
Taylor
Union
Lafayette
Bradford
Suwannee River Water Management District
Dixie
Gilchrist
Gulf of Mexico
Alachua
Santa Fe River Basin
Suwannee River
Levy
Scale in Miles
0
10
20
30
7
Santa Fe River
Ravine Sink
Odgen Pond
Pareners Branch Sink
Sink Well
Oleno Sink
Small Sink
New Sink
Bellamy Rd.
Jims Sink
Hog Pen Pond
Two Hole
Downing Lake
Alligator Rd.
Sweet Water Lake
Santa Fe River Rise
Rise Well
8
Surface and Ground Water Sampling Within OLeno
State Park

• Surface Water Locations
• Sink, Sweetwater Lake, Rise
• Ground Water Locations
• Sink Well, Rise Well
• Sampled during five periods

Date
River Stage (masl)
Period 1
April 28 - May 1, 1998
10.70
Period 2
June 1 - 4, 1998
10.50
Period 3
June 19 - 26, 1998
10.45
Period 4
October 5, 1998
13.43
Period 5
October 13 - 14, 1998
11.90
9
Santa Fe River Stage - OLeno State Park 1998
10
Santa Fe River Sink
Santa Fe River Water Temperature
Temperature (ºC)
Sweetwater Lake
1998
Santa Fe River Rise
11
Correlation of Water Temperature Data
18
17
16
11.25 hours
16 hours
Overland Flow
15
Temperature (ºC)
14
Rise
13
Sweetwater Lake
Sink
12
11
Feb/12
Feb/14
Feb/16
Feb/18
Feb/20
Feb/22
Feb/24
Feb/26
12
River Subsurface Travel Time
13
(No Transcript)
14
Variations in Water Chemistry
Chloride
Low Flow
High Flow
Period 1
Period 5
mg/L
Sweetwater Lake
Sweetwater Lake
Sink Well
Rise Well
Sink Well
Rise Well
Sink
Rise
Sink
Rise
15
Variations in Water Chemistry
Calcium
Low Flow
High Flow
Period 1
Period 5
Sweetwater Lake
Sweetwater Lake
Sink Well
Rise Well
Sink Well
Rise Well
Sink
Rise
Sink
Rise
16
Variations in Water Chemistry
Sulfate
Low Flow
High Flow
75
Period 3
Period 4
60
45
mg/L
30
Sweetwater Lake
Sweetwater Lake
Sink Well
Rise Well
Sink Well
Rise Well
15
Sink
Rise
Sink
Rise
0
17
Conclusions

• Temperature can be used as a natural tracer of
  short residence times
• Mixing of surface and ground water varies with
  river stage
• At low flow, substantial exchange of surface and
  ground water occurs
• At high flow, river water may be injected into
  aquifer rocks
• Unknown ground water sources increase complexity
  of the river system

18
Whats Next?

• Quantify surface water discharge rates
• Ground water contribution
• Determine chemical composition of ground water
  sources
• Determine surface and ground water mixing/exchange