A Study of the Lower Channelized Portion of Spring Creek

 

John R. Chadwick III, Department of Earth Sciences, University of South Alabama, Mobile, AL 36608. E-mail: jrc312@jaguar1.usouthal.edu

 

            In 2002, the lower portion of Spring Creek was physically changed forever. Thirty thousand cubic yards of sediment were removed and a gabion system was installed for bank stabilization and flood control. The project was so outstanding that it received a prestigious award. This study incorporates data from prior studies of the area with new physical characteristics and water quality parameters to see if this award winning project deserves the accolades it received. The physical characteristics recorded consisted of vegetation growth, aquatic life and sediments deposited. The water quality parameters recorded consisted of air/water temperature, dissolved oxygen, pH, alkalinity, hardness and turbidity. It was found that large amounts of sediment have returned to the creek bed and some vegetation like grasses and small shrubs have taken advantage of this. From the water quality data collected it was found that water temperature, dissolved oxygen and pH stayed constant throughout the gabion system but the level of alkalinity and hardness increases as you go down stream. As seen in other studies, limestone is the cause of this increase. Turbidity levels were low throughout the project but it was noted to be less turbid at the base of the gabion system which could be from the backing up of water caused by a debris blockade. Overall Spring Creek seems to be healthy and full of life. Hopefully this study will assist DRCR in evaluating future channelization projects for the watershed.

            Keyword: Spring Creek, gabion, water quality 

 

Introduction

            The Dog River Watershed is located on the northwest side of Mobile Bay and covers about 95 square miles (note: a watershed is the total land area that drains to a common point such as a river or bay). About 60% of the watershed is located within the City of Mobile, with the remainder in suburban and rural areas of Mobile County. The river and its tributaries drain most of the city (Alabama Water Watch 2004). One of these tributaries is the focus of this study.

            Spring Creek is a tributary to Halls Mill Creek which is a tributary to Dog River. In 2002, the lower portion of Spring Creek was physically changed forever. Thirty thousand cubic yards of sediment were removed from Spring Creek and gabions were installed for bank stabilization. Gabions are wire fabric containers that are filled with rocks to form monolithic structures used as retaining walls, sea walls and or channel linings. In comparison to concrete lined channelization projects the modular gabion system seems to be the way to go. Gabions are subjected to forces of tension and compression, the inherent flexibility of the gabion structure enables it to deform rather than break like concrete ones. The efficiency of a gabion system increases rather than decreases with age. During early periods of use the rocks fill with silt and vegetation to form a naturally permanent structure, enhancing the environment (Gabions.net, 2005).  This project extends from just north of US Highway 90 to just south of Halls Mill Road and upstream of the confluence of Spring and Halls Mill Creeks. This area is within the largest remaining bottomland forest in the Dog River watershed, so taking care of this area is of utmost concern (Summersell, 2004).

            The main purpose of the channelization project on Spring Creek was the elimination of the flooding hazard and the bank erosion. The project was so outstanding that it was presented a prestigious award by the Alabama Associated General Contractors of America, Inc. on January 10, 2003 (Land and Water 2003). Now it is 2006, and monitoring of the project has been done ever since the completion of it. This study will incorporate prior baseline data with new physical characteristics and water quality parameters to see if this award winning project deserves the accolades it received.

 

Research Question

            How have the physical characteristics and water quality parameters of the award winning Spring Creek gabion system south of US Highway 90 changed since the completion of the project?

 

Methods

            With this study, the physical characteristics and water quality parameters of the lower portion of Spring Creek within the gabion construction were evaluated. I walked the full length of the channelization project and took a survey of physical characteristics such as vegetation growth, aquatic life, and deposited sediment within the creek itself. I also established three testing sites on the creek from which I obtained water quality parameters (Figure 1).

            The first site was located above the award winning channelization project just north of Hwy 90. The second site was located at the bridge on Halls Mill Rd. which has also been AWW's (Alabama Water Watch) established water quality testing site since before the gabion system was installed. The third site was located at the lower end of the project just south of Halls Mill Rd.

            I visited these three sites and acquired water quality data over the months of March and April between 11:00 in the morning and 14:00 in the afternoon. The chemical monitoring was done using a LaMotte Co. water quality test kit that measured air/water temperature, pH, dissolved oxygen, total alkalinity and hardness ( AWW 2002). I also collected turbidity samples for later analysis at Dr. Frean's office using a LaMotte Co. 2020 Turbidimeter. The meter provided data based on the Nephelometric Method in which the intensity of light scattered, as compared to a standard, will increase as suspended materials reflecting or absorbing light also increases. The intensity is recorded in NTU's or Nephelometric Turbidity Units (Summersell, 2003).

 

Results

            The results of this study where obtained by evaluating new physical characteristics and water quality parameters. The project expands from just north of Hwy 90 to just south of Halls Mill Rd. I took a walk through the full length of the project and observed lots of vegetation and aquatic life. North of Halls Mill Rd. to just south of Demotropolis Rd. I observed small shrubs, multiple grasses, arrowheads, and lots of black berry vines. In this area the creek makes an s-curve and large amounts of sediment have been deposited on both sides of the creek. This build up has aided in the return of the vegetation. I also observed large amounts of sediment in the middle of the creek between Hwy 90 and Demotropolis Rd. that were covered by a dense mat of grasses. From south of Halls Mill Rd. to the lower end of the project there was little vegetation observed due to the water backing up from a large pile of debris just inside the woods. The aquatic life found throughout the project consisted of bull frogs, large mouth bass, blue gill brim, small minnow-like fish and water snakes.

            I looked at water quality parameters at the three test sites I established. These water quality parameters consisted of air/water temperature, pH, dissolved oxygen, total alkalinity, total hardness and turbidity. It was found that the pH levels stayed between 7.5 and 7.0 and that the water temperature generally stayed near 24oC throughout the entire project. The total alkalinity and hardness of the water increased as I went down the gabion system. The turbidity levels were very low throughout the project but I did find that the creek was less turbid at site #3. Dissolved oxygen levels were also recorded and it was found that the percent of saturation stayed above 100% throughout the project as well (Table 1).

 

Table 1: My 2006 Data Averages.

Site

Air Temp.

Water Temp.

pH

DO

% Sat.

Alkalinity

Hardness

Turbidity

1

23C

24C

7

9.3

111

33

30

1.12

2

23C

24C

7.5

10.2

121.5

73

55

1.3

3

26C

24C

7.5

10.8

128.6

78

60

0.56

 

            I also compared the data that I recorded from site #2 to the data collected by AWW at the same site. The data coordinator of AWW Ron Estridge (AWW, 2006) provided me with a compiled list of data that covered from 1995 to 2005 (Table 2). Since my project was done over the months of March and April, I calculated an average for the data received by AWW for those months to see if there were any trends. It was found that since 2002 when the project was completed there was a rise in pH, total alkalinity and total hardness. When compared the same rise was found to be true with my data as well.

 

Table 2: AWW's Test Site Data Averages for 1999-2005 March and April.

Year

Air Temp.

Water Temp.

pH

DO

% Sat.

Alkalinity

Hardness

Turbidity

1999

21.5C

19.6C

6.5

8.3

91.3

39

39

6

2000

23C

22C

6.5

8.9

103.2

30

28

3

2001

24C

22C

6

8.7

99

25

25

5

2002

24C

21oC

6

8.2

93

30

27

3

2003

18C

19C

7.5

8.9

97

82

60

3

2004

25C

23C

8

9.6

113.5

63

70

7.5

2005

22C

24C

7.5

7.4

89

68

45

3.5

 

Conclusion

            In conclusion, this study of Spring Creek will serve as a guide line of data for future studies of the project. In this study questions like "why does the total alkalinity and hardness increase as you go down the creek?" arose. Although increased levels of alkalinity and hardness have little effect on the aquatic life the question can be answered by looking at the materials used in the project. Limestone was utilized in the project and it tends to affect alkalinity and hardness. In future projects this might be avoided by using recycled concrete to fill the gabions instead of limestone. Another question that was brought about was "why is it less turbid at the lower end of the project?". This is simply because of a large debris blockage. Because of the blockage the water has slowed down and allowed for the sediments to settle to the bottom of the creek.

            Overall I believe that the Spring Creek channelization project is performing adequately for now. The gabion system has effectively stopped the bank erosion in the area but due to the accumulation of sediment flooding might return in the near future. With this study I hope to assist Dog River Clearwater Revival in evaluating future channelization projects for the watershed and also help AWW in achieving their goal of developing long-term data sets for establishing water quality trends.

 

References Cited

 

AWW. 2002. Tenth Anniversary Edition. Alabama Water Watch, Water Chemistry Monitoring. Alabama Water Watch. Auburn University, AL.

 

Bob Oertel. Land and Water. 2003. pg 26-29. Prestigious Award for Hobbling Spring Creek.

 

Dr. Bill Deutsch. AWW. 2004. Citizen Volunteer Water Quality Monitoring on Alabama's Coast, Dog River. Alabama Water Watch. Auburn University, AL

 

Gabions.net 2005. Modular Gabion Systems. C.E. Shepherd Co. http://www.gabions.net Accessed on 3-20-06.

 

Ron Estridge. AWW. 2006. 1999-2005 Spring Creek Water Quality Data. Alabama Water Watch. Auburn University, AL.

 

Summersell, S. G. 2004. Spring Creek Revisited. University of South Alabama. Department of Earth Sciences. Mobile, AL.

http://www.usouthal.edu/geography/fearn/480page/03Summersell/revisit04.htm. Accessed on 02-10-06.

 

Summersell, S. G. 2003. Channelization in the Spring Creek Sub-watershed. University of South Alabama. Department of Earth Sciences. Mobile, AL.

http://www.usouthal.edu/geography/fearn/480page/03Summersell/03summersell.htm. Accessed on 02-20-06.