CHANNELIZATION IN THE SPRING CREEK SUB-WATERSHED
G. Summersell, Department of Earth Sciences,
physical change has occurred within the
Channelization, Spring Creek,
Creek is a tributary to Halls Mill Creek within the
In 1994 and 1995 the Alabama Department of Environmental Management (ADEM) conducted two studies on the Dog River Watershed. These studies identified problems and documented the water quality of the Dog River Watershed (DRW), yet Spring Creek had only a vague reference in the second study (Alabama Department of Environmental Management 1995). With the lack of prior documentation and an impending construction project, a study concerning the Spring Creek sub-watershed was of the utmost importance.
assessing Spring Creek’s physical condition, I have acquired baseline data that
will be useful for future studies and have documented the effect of physical
changes to Spring Creek and their relation to the
the modification project to the lower portion of Spring Creek have a
significant impact on water quality of Spring Creek itself and subsequently
Halls Mill Creek and
A qualitative and quantitative assessment of Spring Creek
was necessary to determine any impacts from the construction project. The
qualitative portion consisted of documenting land use within the sub-watershed
from its origin, just north of
The qualitative assessment included a watershed reconnaissance, using topographic and street maps. Reconnaissance began with identifying Spring Creeks sub-watershed by determining high elevations that separate Spring Creek from other creeks using a topographic map. Street maps were used to map out a reconnaissance route. Photographs and detailed field notes recorded initial observations.
Next, a habitat assessment and physical characterization was conducted in accordance with the Alabama Department of Environmental Management’s Field Office Annual Stream Sampling Quality Assurance Quality Control Training Workshop Manual on the proposed construction site and the area upstream of it. Observations made include the following: water quality indicators, flow conditions, riparian land use, and vegetation. It appeared that both areas were previously channelized and allowed to stabilized as evidenced by the presence of fish, an indication of water quality (Cole 1983). It was also observed that there was abundant canopy cover in the riparian zone for the entire length of the creek.
The study’s quantitative portion took explicit measurements in a controlled setting (the construction zone). During this phase, data was collected to address the research question in the form of a time series experiment, “data collected on the same element for the same variable at different points in time” (Mann 2001). Two sampling points were established and are discussed in the results.
In-situ data have been collected using a Hydrolab Surveyor 2/H2O water quality data sonde, which records the following parameters: salinity, conductivity, pH, dissolved oxygen (mg/L), temperature and water depth (meters). The data sonde was calibrated prior to data collection and post-calibrated after data collection to assess the meter’s performance and accuracy. Air temperature was collected using a Fisher Celsius thermometer, placed in the shade before reading. The performance of both the data sonde and the air thermometer were determined to be within acceptable limits throughout the study. Turbidity samples were collected in an individual ¼ gallon plastic containers, preserved on ice at 4°C, and analyzed in the ADEM Field Operations office Laboratory on a Hach Ratio Turbidmeter (Model 18900-00), reported in Nephelometric (NTU) units. The performance of the turbidity meter was determined to be within acceptable limits by the ADEM Laboratory’s internal quality control evaluation.
The parameters that were evaluated are key to evaluating water quality and were collected by the data sonde in the following ways: Salinity was determined by the meter after calibration against a standards solution of standard seawater. This parameter is a measure of the mass of dissolved salt content of water. Conductivity (specific conductance) was also determined by the meter using the same standards solution to calibrate for salinity. Conductivity is a measure of the ability to carry an electric current which is greatest in the presence of inorganic compounds and less with organic compounds (Clesceri, Greenberg, and Eaton 1998).
The data sonde was also used to determine pH. The meter was calibrated against buffer solutions with a pH of 7.00 and 10.00 (pH 4.00 was read at both pre and post calibrations but not calibrated). The best pH range for aquatic life is 6.5 to 8.5 and less than 4.0 or more than 10.0 are considered lethal (Alabama Water Watch 2003).
Dissolved Oxygen (DO) was collected by the data sonde using the electronic method. Membrane electrodes were calibrated using water temperature and barometric pressure to determine a DO saturation percentage (DO %), then calibrated to 100% and reported in mg/L. Aquatic animals and plants require oxygen which enters water from the atmosphere. Streams with adequate shade and that are free of pollution in the form of organic matter have high DO levels and support aquatic life (Alabama Water Watch 2003).
Turbidity is a measure of water clarity, which is impacted by suspended and colloidal matter. Clay, silt, and sand were the greatest cause of high turbidity levels in Spring Creek due to the removal of sediment and channelization. Turbidity was collected as a grab sample that was preserved on ice and later read with a Hach Ratio Turbidmeter. The meter utilized the Nephelometric Method in which the intensity of light scattered, as compared to a standard, will be increased as suspended materials reflecting or absorbing light are also increased. This intensity is recorded in NTU’s or Nephelometric Turbidity Units (Clesceri, Greenberg, and Eaton 1998).
A content analysis of the data collected looks for parameter levels that vary from the norm (parameters collected before the construction project), and how parameters after the project compare to the norm to identify any degradation. Data are presented in the form of graphs to assist in interpreting changes in physical characteristics (Ott 1995).
During the reconnaissance of Spring
Creek, I determined that it has been channelized for
some time from its origin to just south of
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 bales, 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. Routine maintenance will also allow for the removal of garbage from the creek.
site selection was decided on by allowing for an
upstream (of construction site) station designated SC-1 and a station down
stream of the sediment trap, SC-2b. Figure 4 depicts
Spring Creek’s location and sampling points. SC-2a is a downstream sampling
station at the
safety reasons, I established an alternate upstream sampling point at
should be noted that after the establishment of these
upstream sampling points, I discovered an unnamed tributary that enters the
creek between SC-1 and SC-1alt. On
was first evaluated on
Both sites were
Other physical characteristics limits as set forth by ADEM for water bodies with Fish and Wildlife designations are: pH-range of 6.0 to 8.5 or one unit from the normal or natural pH, water temperature- 90°F maximum (there are no industrial thermal discharges to Spring Creek), and Dissolved oxygen (DO)-5 mg/l minimum (Alabama Department of Environmental Management 2001). At no time were any of these criteria exceeded during the study.
The importance of turbidity levels in Spring Creek relates construction work performed and the transportation of material as suspended solids. Turbidity measures the “cloudiness caused by suspended matter” and is “caused by soil erosion and runoff” (Alabama Water Watch 2003). As construction activities clear-cut riparian zone vegetation, the exposed stream banks were allowed to erode into the stream (Figures 6a before and 6b during construction). Also, as equipment entered the creek, the bed load was affected and caused further suspension of sediment. Given these causes, turbidity levels during the construction phase did exceed their limits. To gauge the effectiveness of the construction company’s BMPs to keep erosion on site, portions of the creek must be investigated for deposition of sediment.
The main BMP for the construction
project was the sediment trap at the downstream construction point (Figure 7). This trap is a large basin that “slows water
velocities, thereby allowing soil particles to settle out” (Fifield
and Harding 1992). Though other BMPs were in place
during the project, the trap collects the larger particles of sand, however,
silt and clays are allowed to travel downstream into Halls Mill Creek and
To further investigate deposition, the confluence of Spring
Creek and Halls Mill Creek was reached via a small boat on
With removal of the riparian zone vegetation and loss of cover, water temperature should reach a level equivalent to that of the ambient air temperature resulting in lowered Dissolved Oxygen (DO) rate exclusive from seasonal change (Alabama Water Watch 2003). Table 2 shows the relation of air and water temperature along with dissolved oxygen observed for this study. The average air temperature, water temperature, and DO before the project was air: 13, water: 16, and DO: 7.9. After the project (for the same month last year) air: 20, water: 20, and DO: 9.5. Note that the average air and water temperature is the same, 20 degrees, after construction. While this cannot be the final comparison, it is intriguing that after such a construction project, when air and water temperatures begin to mirror one another and DO should be lower, DO increased.
Judging by the characteristics evaluated during this study, it could be inferred that the significance of modifications made in Spring Creek is relatively low immediately after completion of the construction project. However, lack of significance does not equal lack of importance. These established sampling points would need to be continually evaluated to determine the overall effect on Spring Creek. More work needs to be done to answer questions discovered in this study. For example, there needs to be data collected to explain occasions of lower turbidity and higher DO at the downstream locations than upstream. Future studies will provide data to help answer new questions raised and further catalog the effects of channelization in Spring Creek.
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