Constructing a Detailed Long Profile of the Lower Chippewa River:
Evidence for Stream Incision, Aggradation, and Vertical Stability
Proposal: Project Objectives
Previous collaborative research
with Harry Jol, Garry Running, and several undergraduate students has yielded
compelling evidence of periodic downcutting by the lower Chippewa River (LCR)
since the waning stages of the last major continental glaciation (the Late
Wisconsinan). Downcutting likely began over 15,000 years ago in response to
Mississippi River incision (Kuchta 2011). It then proceeded up the lower
Chippewa River valley (LCRV) in an episodic fashion, resulting in a stair-step
series of stream terraces that become younger in the upstream direction (Figure
1).
Figure 1:
Terraces of the Lower Chippewa River Valley. The Wissota Terrace is the highest
terrace in the valley, and it marks the river’s maximum level of Late
Wisconsinan aggradation. T-6 is the terrace immediately below the Wissota; T-1
is the lowest terrace. Areas along the river are shown are active floodplain.
Note: "OSL" stands for "optically stimulated luminescence;" OSL is a technique
to determine when quartz sand in a sedimentary deposit was last exposed to
sunlight.
From its level of maximum Late
Wisconsinan aggradation to its present elevation, the LCR has incised a total of
30 to 35 meters. And it may still be incising, at least along its upper reaches.
In the 30 km from the Dells Dam to Rock Falls, the amount of active floodplain
below the lowest terrace is small, suggesting that the river has incised
recently or is actively incising. In contrast, a multi-channeled (or
anabranching) section that begins downstream from Rock Falls has the appearance
of a river that is actively aggrading (Huang and Nanson 2007). The same is true
of the 20-km section of river between Round Hill and the Mississippi River.
Between these multi-channeled reaches the river flows primarily in a single
channel bordered by extensive low-lying floodplain with oxbow lakes and other
recent meander features. Along this section the river appears to be vertically
stable and actively constructing a floodplain by lateral migration.
The overarching goal of this
research, then, is to test the hypothesis that different sections of the LCR are
incising, aggrading, or vertically stable. The specific research objective is to
construct a detailed long profile of the LCR to determine if these sections are
characterized by stream gradients that are consistent with incision,
aggradation, and vertical stability. Project Significance We've made great
strides in our past research in reconstructing the geomorphic history of terrace
formation in the LCRV, and have extended our understanding the valley’s
geomorphology well beyond what George Andrews did in his pioneering publication
in 1965. We have not, however, identified clear evidence that the processes of
terrace formation that began in the Late Wisconsinan are still operating and
affecting the modern river. While we can make inferences about present processes
based on the presence or absence of an active floodplain or on variations in
channel planform, we lack other types of field data that would support (or
refute) those inferences. This study is designed to generate data that would
help fill this void.
Project
Plan
If incision is occurring in the
upper section of the LCR, it should be characterized by anomalously steep
reaches or "knickzones" (Simon and Rinaldi 2006). In contrast, if aggradation is
taking 3
place in the
multi-channel sections, they should be located at concavities in the river’s
long profile, with relatively low gradients on the upstream sides and relatively
steep gradients on the downstream sides. Finally, if active lateral migration
and floodplain construction characterize the single-channel section, it should
have a long profile free of knickzones with a consistent gradient.
A long profile of the LCR from
the Dells Dam to the Mississippi is presented in Figure 2. This profile was
constructed using distance and elevation data extracted from maps belonging to
the 1:24,000 topographic map series published by the U.S. Geological Survey. The
contour interval of these maps is 10 ft.
Figure 2: Long profile of the Lower Chippewa River (solid black line). The straight dotted line that roughly parallels the profile is a reference line to help identify where the river is steeper and where it is less steep.
While Figure 2 illustrates fairly well the expected profile concavity caused by aggradation along the multi-channelled reach that begins at a distance of 30 km from the Dells Dam, it overall shows a long profile exhibiting little variability. This apparent lack of variability could be a true characteristic the river, or it could be due to the inherent limitations of the topographic maps used in constructing the long profile. Specifically, those maps have a scale and contour interval that could make it impossible to identify local variations in river slope that active incision or aggradation could produce.
Figure 2: Long profile of the Lower Chippewa River (solid black line). The straight dotted line that roughly parallels the profile is a reference line to help identify where the river is steeper and where it is less steep.
While Figure 2 illustrates fairly well the expected profile concavity caused by aggradation along the multi-channelled reach that begins at a distance of 30 km from the Dells Dam, it overall shows a long profile exhibiting little variability. This apparent lack of variability could be a true characteristic the river, or it could be due to the inherent limitations of the topographic maps used in constructing the long profile. Specifically, those maps have a scale and contour interval that could make it impossible to identify local variations in river slope that active incision or aggradation could produce.
Our proposed project is designed
to overcome the limitations of the 1:24,000 topographic maps for studying the
long profile of the LCR. The main focus of the project is a detailed topographic
survey of the river from the Dells Dam to the Chippewa-Mississippi confluence.
For the survey, we will use a department-owned Topcon total station surveying
system, which consists of a total station (a surveying instrument that combines
a laser distance meter, theodolite, data processor, and data logger), a Topcon
GPS unit (which provides geographic coordinates via a Bluetooth connection to
the total station), and a prism pole with prism (which is the target for the
total station laser beam). We plan to survey the river in 4 approximate 1-km long sections,
and in each we intend to survey the water surface of the river every 100 m or
so. (Survey sections will be shorter in places where local conditions negatively
affect sight distance from the total station.)
As we work our way down the river, we will periodically tie into bench marks to ensure that our surveyed elevations are correct. Benchmarks, which are maintained by county land records offices, are commonly located where section lines intersect the river. We will acquire the precise locations of BMs that we can tie into from the land records offices of the various counties through which the LCR flows. The proposed surveying work will require a crew of three people – one to operate the total station, one to operate the GPS unit, and one to be responsible for the survey prism. It will also require boats for accessing survey sites – a two-person canoe for the total station and GPS people, and a single-person kayak or canoe for the prism person. With a 3-person crew, I estimate that we will being able to survey five to ten kilometers of river per day. At that rate, surveying the entire length of the LCR will take 10 to 20 full days. We will do the proposed field work as weather conditions allow in late July and August when streamflow is typically near its lowest for the year and varies little from day to day.
In addition to the field work, I and my collaborators will spend considerable time downloading data from the total station, backing it up, and analyzing it. We will use bad-weather days during the field season to accomplish some of this work, but much of it will doubtless be done during the Fall semester. We will also spend time in the Fall preparing and presenting results at an academic conference. Nature and extent of student and faculty/staff mentor activities and involvement.
Two students will be intimately involved in all aspects of the proposed research. While none have committed to the project yet, I know of a couple who are interested in collaborating with me on summer research. Both student researchers will be responsible for helping out with fieldwork logistics this summer and for making the field component of the study a success. Both will be responsible for downloading, organizing, and backing up data, and both will play a role in analyzing the field data and preparing the results for presentation. I, as faculty mentor, will work closely with the students in the field 5 this summer, and I will meet with them regularly and provide guidance as they work on the office component of the research.
Plan
for dissemination of the results
As we work our way down the river, we will periodically tie into bench marks to ensure that our surveyed elevations are correct. Benchmarks, which are maintained by county land records offices, are commonly located where section lines intersect the river. We will acquire the precise locations of BMs that we can tie into from the land records offices of the various counties through which the LCR flows. The proposed surveying work will require a crew of three people – one to operate the total station, one to operate the GPS unit, and one to be responsible for the survey prism. It will also require boats for accessing survey sites – a two-person canoe for the total station and GPS people, and a single-person kayak or canoe for the prism person. With a 3-person crew, I estimate that we will being able to survey five to ten kilometers of river per day. At that rate, surveying the entire length of the LCR will take 10 to 20 full days. We will do the proposed field work as weather conditions allow in late July and August when streamflow is typically near its lowest for the year and varies little from day to day.
In addition to the field work, I and my collaborators will spend considerable time downloading data from the total station, backing it up, and analyzing it. We will use bad-weather days during the field season to accomplish some of this work, but much of it will doubtless be done during the Fall semester. We will also spend time in the Fall preparing and presenting results at an academic conference. Nature and extent of student and faculty/staff mentor activities and involvement.
Two students will be intimately involved in all aspects of the proposed research. While none have committed to the project yet, I know of a couple who are interested in collaborating with me on summer research. Both student researchers will be responsible for helping out with fieldwork logistics this summer and for making the field component of the study a success. Both will be responsible for downloading, organizing, and backing up data, and both will play a role in analyzing the field data and preparing the results for presentation. I, as faculty mentor, will work closely with the students in the field 5 this summer, and I will meet with them regularly and provide guidance as they work on the office component of the research.
The results
of this research will be presented at an academic conference (such as at the
regional conference of the West Lakes Division of the Association of American
Geographers in November) and at Student Research Day next Spring. In addition,
the results will be included in future manuscripts about the geomorphic history
of the LCRV that I, Harry Jol, and Garry Running (hopefully with student
collaborators) will be submitting for publication in peer-reviewed
journals.
References Cited
Andrews, G.W. 1965. Late Quaternary Geologic History
of the Lower Chippewa Valley, Wisconsin.
Huang, H.Q., and Nanson, G.C. 2007. Why some rivers develop an anabranching pattern.
Kuchta, M. 2011. Late Quaternary terrace and long profile development in the Lower Chippewa Valley.
Simon, A., and Rinaldi, M. 2006. Disturbance, stream incision, and channel evolution: the roles of excess transport capacity and boundary materials in controlling channel response. Geological Society of America Bulletin 76: 113-124. Water Resources Research 43, W07441, doi:10.1029/2006WR005223. Geological Society of America Abstracts with Programs 43(5): 508. Geomorphology 79: 361-383.
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