SPRING CREEK REVISITED

 

Steven G. Summersell, Department of Earth Sciences, University of South Alabama, Mobile, AL 36608. Email: stvnlusmsl@aol.com.

 

 In the Spring of 2004 an urban stream within the Dog River watershed was evaluated one year following a study that recorded the physical characteristics of the construction project before, during, and after bank stabilization was performed. The bank stabilization project was completed on the lower portion of Spring Creek just above a pristine, bottomland forest that forms the confluence with Halls Mill Creek. In-situ data was collected using a water quality data sonde, which recorded the following characteristics: salinity, conductivity, pH, dissolved oxygen (mg/L), temperature and water depth.  Turbidity samples were collected and later analyzed using a turbidity meter. Content analysis of the data were inconclusive and left lingering questions concerning the downstream portions of the creek.  The second year’s study evaluated the same parameters using identical methods. The goal of the second study was to evaluate Spring Creek’s condition one year after the original study and investigate the irregularities found in the downstream portion.

 

Keyword: Channelization, Spring Creek, Dog River watershed.

 

 

Introduction


Spring Creek is a tributary to Halls Mill Creek within the Dog River watershed, located in Mobile, Alabama.  In mid February 2002 the lower portion of Spring Creek underwent physical modifications (see Figure 1). Thirty thousand cubic yards of sediment were removed from Spring Creek and gabions were installed for bank stabilization. This project extended from US Highway 90 to south of Halls Mill Road and upstream of the confluence of Spring and Halls Mill Creeks. The confluence area is within the largest bottomland forest in the Dog River watershed.  A study of the modifications, before, during and after was necessary to assess the overall health of the sub-watershed and any effect modification may have had on Spring Creek.

 The second year’s study evaluated the same parameters using identical methods. The goal of the second study was to evaluate Spring Creek’s condition one year after the original study and investigate the irregularities found in the downstream portion.

 

 

Research Question


What is the current status of the lower portion of Spring Creek one year after a major channelization project?



Methods

 

            The second year’s study evaluated the same parameters using identical methods. In-situ data was collected using a water quality data sonde, which records the following parameters: salinity, conductivity, pH, dissolved oxygen (mg/L), temperature and water depth (meters). Turbidity samples were collected in an individual ¼ gallon plastic container, preserved on ice to 4°C, and analyzed in the ADEM Field Operations office Laboratory on a Hach Ratio Turbidmeter (Model 18900-00), reported in Nephelometric (NTU) units.

            A content analysis of the data collected will look for parameter levels that vary from the norm (parameters collected before the construction project), and how parameters after the project will compare to the norm to identify any degradation.  Data are presented in the form of graphs to assist in interpreting changes in physical characteristics.

 

 

Results

 

The construction project was titled “Spring Creek Phase 1B” and encompassed the removal of 30,000 cubic yards of sediment from Spring Creek and the construction of stream bank stabilizers (gabions). The total disturbed area was 4.9 acres and best management practices (BMPs) included a large sediment trap, silt fences, hay bails, grass matting, hydroseeding of slopes, and a total bypass (pumping around the site) of the creek during sediment removal and gabion placement. The sediment trap is a permanent fixture and will allow for the removal of future construction sediment. The characteristics evaluated during the first study inferred that the significance of modifications made in Spring Creek was relatively low immediately after completion of the construction project (see Figures 2 and 3). Figure 4 depicts Spring Creek’s location and sampling points..

            The main BMP for the construction project was the sediment trap at the downstream construction point .This trap is a large basin that “slows water velocities, thereby allowing soil particles to settle out” (Fifield and Harding 1992). Over time and as future upstream bank stabilization projects are carried out, this trap should collect sediment accumulations and was designed to be a removal point with routine maintenance. In the beginning of the second study, the condition of the trap was one of neglect as the trap was completely filled in.

Figures 7 and 8 also show the extent of sedimentation. Both pictures are of the Halls Mill Road bridge over Spring Creek in their various phases of the project. Average depth readings at this location have changed from 0.5 meters immediately after completion of the construction project to 0.16 meters for the second study, essentially the creek depth has become 0.34 meters (1.1 feet) shallower.         

Figures 9 and 10 contain the 3 main parameters evaluated in both studies, Turbidity, Dissolved Oxygen, and Salinity. There is a difficulty in reevaluating water bodies from year to year due to seasonal change (Burton and Pitt 2002). The problem of seasonality is further compounded by the fact that the creek has undergone such a drastic change.

Of particular interest was the slight increase in Salinity. It was previously assumed that Spring Creek was not tidally influenced upstream to the construction site. Yet, it was noticed during the first study that after completion of the construction project, there was a lower occurrence turbidity and higher DO at the downstream locations than at the upstream location. A review of the data further indicated that this was also true of Salinity. This is a strong indication of tidal influence. It should be noted that at the beginning of the construction project, a large beaver bam was removed resulting in a noticeable lowering of the creek’s water level, even as high up as the further most sampling point, SC-1alt.

A review of the topography in the area shows that the lower portions of the study area are within the 10 foot contour line. According to the Alabama Department of Environmental Management (ADEM) Administrative Codes, a coastal area is defined as being located “seaward of the continuous 10 foot contour” and hence maybe subject to tidal influence.  However, Interstate 10 is seaward of the study area and field investigations were needed to shed light on the question of tidal influence (ADEM 1995).

            A small body of water resembling a lake was noticed and tidal flow into this “lake” was also noted. Figures 11 and 12 show the location of the lake. With its proximity to the confluence of Spring Creek and Halls Mill Creek, make it possible that tidal observations at the lake could also indicate tidal influence of Spring Creek within the study area. This may answer the question raised in the original study of increased salinity in the downstream sampling locations.

            How the lake was formed is unknown. It was initially thought that it may be a remnant of the artificial lake  of Hall’s mill. However, in a historic map (Township 5 South, Range 2 West, As recorded in Township Map Book 2, page 57, 1800's), Hall’s mill is situated in the 15th section; the present day lake is in the 14th (Probate Court of Mobile County, AL 2004).
             A possible explanation can be found in the US Geologic Survey’s technical report on road construction modifying surface water flow in Florida. In the report, road construction “act(ed) as an earthen dam that impounded creeks…blocking the natural movement of creeks in coastal areas, thus altering water salinity”. The report further stated that, “adjacent creeks commonly flowed into one another during high-water conditions, thus allowing the transfer of water from one drainage basin to another”. The impoundment effect could be due to construction of I-10 thus forming the lake (USGS 2004).
            After the discovery of tidal exchange in the area, one must consider how the force of the incoming tide can overpower stream flow to allow water with higher salinity up to the sampling sites. Levinton explains that fresh water from a stream can have a lower density than that of the incoming water and is forced up by the denser saline water. This phenomena has been observed in the Chesapeake Bay estuarine system

(Levinton 2001).

            With the changes to the hydrology in the area, one must consider the whole of Dog River, Halls Mill Creek, Spring Creek, and any adjacent creeks as one estuary with one affecting the other. To that end, data was needed to gage the overall effect Spring Creek has to its receiving water, Halls Mill Creek.

This could entail a study whole and unto itself and with limited resources a full study could not be achieved. It was decided to collect turbidity samples of Halls Mill Creek upstream and downstream of the confluence with Spring Creek. These two different sample locations would provide data of Spring Creek’s effluence to Halls Mill Creek. The following observations were made:

            There was a rain event on 2/26 that accounts for the high turbidity level at Halls Mill Creek Upstream, yet notice the relatively low turbidity on Spring Creek for that same day. Stranger still is the very low turbidity reading that same day on the downstream sample of Halls Mill Creek. It is highly unlikely that Spring Creek could mix well enough with Halls Mill to reduce its turbidity so drastically. A sand slug originating on Halls Mill Creek and not Spring Creek was noticed just down stream of the confluence during the original study.

            A man made channel was found connecting the lake and Halls Mill Creek just east of the I-10 Bridge. It should also be sampled to see if it flows into Halls Mill Creek during rain events, however, rain events were inadequate after its discovery.

 

 

Conclusion

 

            Though difficulties arose in comparing data due to seasonal change, some lingering questions from the original study were addressed. Higher Dissolved Oxygen and Salinity could have been due to water from Halls Mill Creek entering the study area along with the incoming tide. Due to dynamic changes in the hydrology of the study area, the research question would be better answered with more long term trend data as the dynamics are still fluctuating.

            The results of Turbidity testing on Halls Mill Creek show a possible relation to Spring Creek discharging less turbid water in to Halls Mill Creek. This relation, along with the discovery of a lake in the study area should also be included in a future study.

There is a lack of knowledge of the interactions the Spring Creek Sub-watershed has with not only Halls Mill Creek, but also Dog River.

            This need to study a target sub-watershed along with adjacent watersheds has been identified by John Lehrter in his dissertation, “Estuarine Ecosystem Metabolism and Retention of Allochthonous Nutrient Loads in Three Tidal Rivers Estuarine Systems” (Lehrter 2003). Lehrter’s multiple watershed approach is the basis for an upcoming Mobile Bay National Estuary Program funded project to be preformed by the Mobile Branch of the Alabama Department of Environmental Management.

            The NEP/ADEM study will simultaneously evaluate multiple watersheds within the greater Mobile Bay watershed. While streams and creeks such as Spring Creek will be included in the study, more emphasis will be placed on the interactions between sub-watersheds and there accompanying estuaries.  

            The second year Spring Creek study (Spring Creek Revisited), has shown that there is more interaction between Spring Creek and Halls Mill Creek and Dog River than was previously thought. Data and observations from both the original study (Channelization in the Spring Creek Sub-Watershed) and the second Study (Spring Creek Revisited), has recorded the changes the creek has undergone and discovered that there are other influences that should be evaluated as well. It is only after these aspects have been investigated that Spring Creek’s importance to the Dog River Watershed can be fully understood.

 

 

References

 

Alabama Department of Environmental Management (1994). A Survey of the Dog River

Watershed: An overview of land use practices and an assessment of the effects

of development on the natural resources of the basin. (ADEM Technical Report)

Mobile Branch, Mobile, Alabama.

 

Alabama Department of Environmental Management (1995). A Survey of the Dog River

Watershed, Second year’s findings: A review of ongoing development in the

watershed and assessment of the effects of urban non-point sources on the aquatic resources of the basin. (ADEM Technical Report) Mobile Branch, Mobile, Alabama.

 

Alabama Department of Environmental Management (1995). Administrative Code, Division 8,  Coastal Program. Montgomery, AL.

 

Burton, G. and Pitt, R.(2002). Stormwater Effects Handbook. Lewis Publishers, Boca Raton, FL.

 

Lehrter, J. ( 2003). “Estuarine Ecosystem Metabolism and Retention of Allochthonous Nutrient Loads in Three Tidal Rivers Estuarine Systems” . University of Alabama.

 

Levinton, J. (2001). Marine Biology, 2nd ed.. Oxford University Press, New York, NY.

 

Probate Court of Mobile County, Alabama (2004). Township 5 South, Range 2 West, As recorded in Township Map Book 2, page 57, 1800's. Provided by M. Fearn, Ph.D.

 

Summersell, S.G. (2003). Channelization in the Spring Creek Sub-Watershed”.

University of South Alabama Department of Earth Sciences, Mobile, AL.

 

 US Geologic Survey (2000). “Assessment of the Effect of Road Construction and Other Modifications of Surface-Water Flow at St. Vincent National Wildlife Refuge, Franklin County, Florida”. US Geologic Survey Water Resource Investigations Report 00-4007.

 

Volkert and Associates, Inc. (2004).  Drainage Services. Accessed 4/25/2004. http://www.volkert.com/Services/Drainage%20Services.htm