CAUSES FOR CHANGE IN STREAM-CHANNEL MORPHOLOGY
Chad A. Whaley, Department of Earth Sciences, University of South Alabama,
MobileAL, 36688. E-MAIL: caw408@jaguar1.usouthal.edu
The ultimate goal of this project was to determine the causes for change in stream
channel morphology. With the use of Geographic Information Systems, a horizontal
profile of Spring and Moore Creeks was created. The examination of both these profiles
can help us understand and analyze the causes of erosion, sand deposits and sediment
transport by measuring elevation changes. By comparing the elevation changes from the
profile with the actual land, it can then be determined if changes in the stream channel are
due to human or natural causes. Findings supported a conclusion that changes in
elevation along both creeks were due to human activity. Long-term adjustments can now
be made in relation to drainage changes or base-level changes through the use of
horizontal profiling. This technique can be useful for predictions of up to several decades,
which can in turn provide valuable information to the surrounding community and Dog
River Clearwater Revival.
Keyword: stream, channel, morphology, Geographic Information Systems,
horizontal profiling, sedimentation.
Introduction:
Covering a total area of approximately ninety-five square miles, The Dog
River Watershed (DRW), encompasses most of Mobile’s streams and creeks. Nearly
60% of the watershed lies within in the city’s boundary. Dog River serves as not
only a drainage way for Mobile, but also as recreational waters for surrounding
residents (ADEM, 1994). As with any watershed, there are major concerns that affect
people and the environment in a variety of different ways. Erosion, runoff, sediment
transportation, deposition are just a few of the concerns. To better understand the causes
of these watershed problems, research has been conducted on changes in stream channel
morphology within the Dog River Watershed.
Geomorphology is the study of landforms including the origin, evolution and the
processes that form them. These processes are each influenced differently by climate,
ecology, and human activity. Present day structures are studied not only to help us
understand the geological features we see today and the forces that created them, but also
to help us understand the features from previous ages that we see recorded in geological
history (Schumm 1977).
River morphology is the field of science dealing with changes of river form and
cross-section shape mainly due to sedimentation and erosion processes. River
morphology is a complex subject, which can be subdivided into several different areas
that are often related to each other. These areas include: overland flow and channel flow,
drainage systems and channel networks, stream channels, stream flow, and stream stages,
stream discharge and basin area, horizontal profiling and profile development, stream
erosion and transportation (Schumm 1977). The focus of this research is the aspect of
horizontal profiling on stream channels.
A good way to understand stream channel morphology is to conduct a
horizontal profile of the actual streams. The monitoring of the profile can help us to
understand and analyze the causes of erosion, sand deposits and sediment transport by
measuring elevation changes across set transects on a stream over time (Russell, 1895).
Streams, creeks and rivers are all landforms that are subject to rapid change in
channel shape and flow pattern. Water and sedimentation build up can determine the
dimensions of a stream channel (width, depth, meander wavelength, and gradient).
What is the significance? The physical features of stream channels reflect the magnitude
of water and sediment discharges. In the absence of different hydrologic data, an
understanding of stream morphology through horizontal profiling, can help to conclude if
any environmental changes have taken place (Chang, 1988).
When looking at changes in stream channel morphology, people often wonder
why these changes have taken place. Are the changes due to human or natural causes or
even both? Land use changes, such as land clearance, construction, farming and forestry
can all have an effect on streams and rivers. Climatic events such as heavy rainfall,
flooding, and tectonic activity are believed to be the primary cause for morphology
changes. Assumptions are also being made that human activity is to blame for
changes in stream morphology over time.
Research Question:
It has been my research goal to examine changes in stream morphology by
horizontal profiling and to assess if the changes were associated with management,
topography or other factors. Are there similarities and/or differences in the morphology
of nearby streams? Is there some natural or human cause for erosion, sedimentation
transport or deposition in a certain area of the streams’ profile? What are the causes?
Through the use of Geographic Information Systems (GIS), I will inform the surrounding
community that horizontal profiling can prove beneficial to the assessment of the causes
and effects regarding changes in stream channel morphology.
Methods:
Geographic information system (GIS) is a computer system capable of
integrating, storing, editing, analyzing, sharing, and displaying geographically-referenced
information. In a more generic sense, GIS is a tool that allows users to create interactive
queries (user created searches), analyze the spatial information, edit data, make maps, and
present the results of all these operations(Goodrich 2007). The goal of this study was
to derive predictive relationships for stream channel characteristics using a highresolution ArcInfo GIS database.
I chose Spring and Moore Creeks, located in the Dog River Watershed, to
examine in my study. Utilizing GIS technology, I investigated the morphological
relationships of the two creeks previously mentioned.
The City of Mobile offers a wide variety of shape files that can be used to produce
various types of maps using GIS software. Obtaining the data for Dog River Watershed
area, streams, water bodies, major roads, 2-foot contour lines and an aerial photograph of
the City of Mobile
was the first step in
the process. The
area of Spring and
MooreCreeks,
Figure 1, were
selected from the
watershed data file.
With this specific
area, I created a
map using ArcMap,
a GIS software with
the capabilities
Figure 1: Dog River Watershed, Mobile AL.
Source: Dog River Watershed Website 2007
of producing, editing
and analyzing maps of all varieties. I displayed streams, major roads, bodies of water and
the aerial photograph of the city designated area. To measure or analyze any elevation
changes, a surface layer had to be created in order to make observations and derive
conclusions. Using the topographic to raster image function in ArcMap spatial analyst, a
surface layer was created from the 2-foot contour file (2002) of the Spring and Moore
Creek’s vicinity. With an elevation surface now established on a map, the horizontal
profile of the two creeks could then be created. The length of Spring and Moore Creeks
were then digitized from the head waters (beginning) down to the mouth (end) of both
creeks. Horizontal profiles of Spring and Moore Creeks were then established. Studying
the completed profiles and analyzing the creeks’ elevation changes, I then measured
distances along both creeks in the map so that reference points could be made on the
profile graphs. Once reference points were accounted for, I then chose two sites along
each creek where there were obvious changes in elevation. I went out in the field to the
actual creeks and compared and contrasted the data that was presented to pin point the
causes of change in morphology whether natural or manmade.
Results:
After creating a horizontal profile for both Spring and Moore Creeks and doing
field observations, I came to the conclusion that the most drastic elevation changes in the
profiles were due to human activity or manmade causes. From the horizontal profile of
Spring Creek, Figure 2, two sites on the graph were chosen that were of interest. The
first major elevation change was simply due to a major road, Cottage Hill, being in
the path of the creek. Also located here was a large pond which was only visible from an
aerial photo of this particular place, (Figure 3). The elevation gradually decreased by
Cottage Hill
Rd
Government
Blvd.
Girby Rd.
Demetropolis
Rd.
Halls
Mill Rd.
Figure 2: Horizontal Profile of Spring Creek
Source: City of Mobile GeoDatabase, 2007
the pond and then increased
as the creek approached
Cottage Hill Rd. The
elevation again began to
decrease on the other side
of the road. A very drastic
change in the graph occurred
towards the mouth of the
creek where there were four
simultaneous peaks in
Figure 3: Spring Creek at Cottage Hill Rd.
Source: City of Mobile GeoDatabase 2007
elevation. This is where Spring
Creek crosses four major roads, Girby Rd., Government Blvd, Demetropolis Rd., and
Halls Mill Rd. At the corner of Government and Demetropolis is an elevated shopping
center which also leads to differences in elevation, (Figure 4). With respect to Spring
Creek, my research
concluded that any
morphologic
changes were a
result of manmade
changes to the
landscape, through
the construction of
ponds, shopping
centers, parking lots
and major roads.
Figure 4: Spring Creek at Government Blvd.
Source: City of Mobile GeoDatabase 2007
When examining the horizontal profile of Moore Creek, (Figure 5), and making
field observations, the conclusion was made that the changes in stream morphology were
also due to human activity. The first major change in elevation was where Moore Creek
ran underneath Government Blvd. On the south side of Government Blvd. There were a
series of drop offs causing the first significant drop in elevation, (Figures 6 & 7). On the
north side of Governemnt Blvd., I noticed some sedimentation buildup upstream. The
elevation peaked at Government and decreased rapidly due to the drop offs. The
other drop in elevation was due to a manmade dam where Moore Creek meets the
Montlimar Canal at Halls Mill Rd, Figure 8. There was also some sedimentation buildup
upstream from the dam. I did not find any other changes in morphology.
Government Blvd.
and series of
manmade drop offs
Moore Creek
meets Montlimar
Canal at Halls Mill
Rd.
Figure 5: Horizontal Profile of Moore Creek
Source: City of Mobile GeoDatabase 2007
Figure 6: Moore Creek Embankment
@ Government Blvd.
Figure 7: Moore Creek Embankments
@ Government Blvd.
My research concluded that changes in Moore Creek were a result of manmade changes
to the morphology through the construction of roads, small dropoffs, and a small dam.
Figure 8: Dam where Moore Creek meets the Montlimar Canal.
Discussion and Conclusions:
An emerging interest in environmental quality highlights the importance in
determining what the natural and human impacts are on streams and rivers. In the
absence of data such as water flow rates, sediment deposits, or other hydrologic
parameters, analyzing and monitoring stream morphology through horizontal profiling
proves to be very useful and beneficial. With natural impact and human causes such as
urbanization and construction, runoff and sediment loads increase, causing geomorphic
changes in size and form. In the Spring Creek profile, noticing 4 peaks in elevation due to
the presence of roads is a possible indicator that sedimentation might occur between these
peaks of elevation. It is extremely important to understand and predict these channel
changes since they are often associated with flooding, sedimentation, water quality, and
even fish habitat problems (Leopold, 1915). There are so many ways and techniques
used to study the physical character of stream channels. Hydrologic parameters such as
channel flow direction, flow rates, deposition of sediments, slope, roughness, bedmaterial size, cross sectional shape, erosion/runoff and an understanding of stream
morphology, can help identify environmental changes of many sorts (Harrelson 1994).
Due to certain technical and timing issues though, geomorphologic analysis on large and
complex study areas has been prohibitive. With the advent of Geographic Information
Systems, watershed and hydrologic modeling can now be carried out rapidly and
accurately. With the completed research, I anticipate that the Dog River Clearwater
Revival will gain valuable information on the causes for change in stream channel
morphology through the horizontal profiling. It would be in my interests to further my
research and to conduct a more complex study on river geomorphology through the use
of GIS and field observations in the Dog River Watershed.
References Cited:
ADEM. Alabama Department of Environmental Management. 1994 A Survey of the
Dog River Watershed Mobile.
Chang, H.H. 1988. Fluvial processes in river engineering. New York: John Wiley &
Sons.
City of Mobile GeoDatabase, GeoDatabase, no date
http://maps.cityofmobile.org/metadata/geodatabasename.aspx (20 March 2007)
Goodrich, David C., Guertin, Phillip D., and Miller, Scott N. 2007. Investigating Stream
Channel Morphology Using a Geographic Information System.
http://gis.esri.com/library/userconf/proc96/TO300/PAP291/P291.HTM (13 March 2007)
Harrelson, C.C., C. Rawlins, and J. Potyondy, 1994. Stream Channel Reference Sites: An
Illustrated Guide to Field Techniques. USDA Forest Service Rocky Mountain Forest and
Range Experiment Station General Technical Report RM-245, 67 p.
Leopold, Luna B., Miller, John P., Wolman, Gordon M. 1915. Fluvial processes in
geomorphology. San Francisco, W. H. Freeman, 1964
Russell, Richard J. 1895. River and delta morphology. Baton Rouge, Louisiana State
University Press, 1967.
Schumm, S. A. 1977. The fluvial system. New York: John Wiley & Sons.