CHANNELIZATION IN THE SPRING CREEK
SUB-WATERSHED
Steven
G. Summersell, Department of Earth Sciences,
A
physical change has occurred within the
Keyword:
Channelization, Spring Creek,
Spring
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.
By
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
Did
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.
Sampling
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
For
safety reasons, I established an alternate upstream sampling point at
It
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
SC-1
was first evaluated on
Both sites were
revisited on
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.
On
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
ultimately
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.
Alabama
Department of Environmental Management (1994). A Survey of the
Alabama
Department of Environmental Management (1995). A Survey of the
Alabama
Department of Environmental Management (2001). Methodology for
coastal watershed assessments.
(ADEM Technical Report) Mobile Branch,
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Cole, Gerald A.
(1983) Textbook of Limnology (3rd ed.)
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erosion and sediment control.
Mann, Prem S. (2001). Introductory Statistics (4th
ed.)
Ott, Wayne R. (1995). Environmental
Statistics and Data Analysis.
Rosgen, Dave (1996). Applied
River Morphology.
