reyurchisin
Registered: October 2013
City/Town/Province: Huntingdon
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Abstract
In the summer of 2012, the Cleveland Metroparks (CMP) began a plan to assess stream bank erosion potential within the Cuyahoga River Watershed using Rosgen’s modified Bank Erosion Hazard Index (BEHI). The BEHI rates six metrics: bank angle and height, root depth and density, bank material and stratification and assigns point values for each factor to calculate a score that indicates each site’s streambank erosion potential. The project was designed to identify and map sources of sediment pollution and to prioritize restoration projects that retain and restore stream banks to their natural disposition. The assessment conducted involved a Class III primary headwater stream named “Echo Mills” and an additional unnamed Class II headwater stream, located within the CMP Brecksville Reservation. Eighty-four sites were assessed on “Echo Mills” with fifty-three sites (63%) recording scores for high or very high potential for erosion. Seventy-two sites on the Class II stream were assessed with twelve sites (16.7%) recording scores for high or very high potential for erosion. The BEHI emphasizes the importance of streambank materials, often elevating sites into the high or very high range based on the presence of highly erodible, non-cohesive materials such as gravel and sand. Results suggest that “Echo Mills” evidenced higher erosion potential overall than the unnamed stream when considering that approximately 60% of the “Echo Mills” sites recorded sand as the dominant bank composite, whereas 8.3% of the unnamed stream sites were comprised of sand, causing it to be less susceptible to potential erosion.
Key Terms
Stream bank stratification sediment storm water erosion
Riprap riparian zone
Introduction
Sediment is one of the principle pollutants of surface waters of the United States and sediment eroded from stream bank failures has been found to be the single largest contributor to suspended sediment loads to streams draining unstable systems in the mid-continent (Simon et al., 2004). Additionally, accelerated streambank erosion is a major cause of non-point pollution (Rosgen, 2001) that is associated with the increased volume and rate of urban stormwater runoff. The rainwater or melted snow has the potential to erode stream banks and stream beds; dislodging and suspending sediment that might otherwise have remained in place. Erosion can be gradual, or can occur rapidly through a sudden collapse of a streambank (Booth, 1990). Increased sediment loads affect water quality and the shape and dimension of river channels, thereby altering aquatic habitat and channel stability (Rosgen, 1993). A major factor that affects the sediment yields for the Cuyahoga River is bank erosion of tributaries which contributes to approximately 187,000 tons of sediment annually (Source: Water Quality Lab, Heidelberg College). Furthermore, when these sediments are dredged to remove the excess deposits from harbors and transportation routes, these sediments are often concentrated with heavy metals and toxicants that further reduce water quality and increases costs for filtration and disposal. In the summer of 2012, the Cleveland Metroparks (CMP), Division of Natural Resources, in partnership with the Northeast Ohio Regional Sewer District’s Stormwater Management Program (NEORSD), began a plan to assess stream bank erosion potential within the Cuyahoga River Watershed (CRW). The project is designed to identify and map sources of sediment pollution that diminish the quality of the drinking and recreational water supply and to prioritize restoration projects that retain and restore flood plains, riparian zones, and stream banks to their natural disposition. The assessment conducted involved a Class III primary headwater stream named “Echo Mills” and an additional unnamed Class II headwater stream, both of which are tributaries of the Cuyahoga River located within the CMP Brecksville Reservation.
Streambank erosion can be traced to two major factors: stream bank characteristics (erodibility potential) and hydraulic/gravitational forces (Rosgen, 2001). The processes by which streambanks erode include: surface erosion, mass failure, particle shearing, freeze-thaw, ice scour and liquifaction/collapse (Rosgen, 2001). Streambank erosion is a natural process, but acceleration of this natural process due to urbanization and stormwater runoff leads to disproportionate sediment supply, stream channel instability, land loss, habitat loss and other adverse effects (United States Environmental Protection Agency, 2012). Determining the potential for streambank erosion either by natural or by improper land use practices and urbanization was often difficult to distinguish until the Bank Erosion Hazard Index (BEHI) was created by David L. Rosgen, P.H. of Wildland Hydrology, Inc. (Rosgen, 2001). This model was developed by identifying several key stream bank characteristics that indicate erosion potential and assign point values for each factor to determine a rating for each site being investigated. Once the point values are determined, the overall score indicates a risk rating of very low, low, moderate, high, very high, and extreme potential for erodibility.
Previous studies evidenced that stream bank erosion contributions were shown to be the majority of total sediment supply in the West Fork Madison River, Montana (Rosgen, 1973, 1976). Streambank erosion contributed 49 percent of the total annual sediment yield from three miles of unstable channel on the East Fork San Juan River, Colorado caused by willow eradication in the 1930’s (Rosgen, 2001). Lateral streambank erosion may be accelerated in systems that have been hydraulically affected by changes in land-use, removal of riparian vegetation, and/or changes in channel dimension from activities, such as, in-stream gravel removal. Accelerated lateral erosion contributes additional sediment to the stream network that can impact water quality and increase the potential for river instability (Van Epps, et al. 2002). Simon (1989) reported lateral bank erosion rates from the Forked Deer River system in West Tennessee at 1.5m/year representing a bank erosion contribution of 82 percent of the 10 million tons/year, with 18 percent contributed by bed degredation. In the past, most research was conducted for western streams; in January, 2011, the US Army Corps of Engineers provided a workshop to the Cleveland Metroparks, the Northeast Ohio Regional Sewer District and other interested parties to educate and implement practices that will decrease bank erosion rates, reduce sediment supply, improve aquatic and land habitats, and aid in stormwater management (reducing urban runoff), thereby bringing best practices to the eastern streams.
Erosion of stream banks and stream beds are not the only negative effects of urban stormwater runoff; urban runoff can harm aquatic life in many ways due to changes in water chemistry and habitat loss (US EPA, 1997). When stormwaters transport eroded material downstream, inevitably, sediment settles and macroinvertebrates and their eggs can become covered, causing death and loss of habitat (Michaud, 1991; and Moore, 1989). Sediment suspended in water increases infection and disease among fish by irritating their gills and reduce the survival rate of fish eggs. Suspended sediment scours submerged plants attached to rocks, as well as blocks sunlight that aquatic plants use to produce growth through photosynthesis (Schueler, 1997). Futhermore, sediment may carry nutrients, bacteria, toxic metals and organic chemicals to the water (Horner, 1994) which cause eutrophication and may have negative effects on the immune systems and early development of aquatic life (Colborn, Dumanoski, and Myers, 1997). In addition, stream bank erosion also causes changes in hydrology which affect the shape and dimension of river channels, thereby altering aquatic habitat (Rosgen, 1993). The changes in water flow alter temperature and dissolved oxygen levels possibly threatening insect and fish populations. The impacts of sedimentation, contaminant loadings, eutrophication, and hydrologic instability not only threaten individual animals, but also reduce the diversity of life living in these waterbodies (Schueler, 1994).
The objective of this study was to identify erosion hot spots and collect data regarding two tributaries of the Cuyahoga River located in the Brecksville Reservation of the Cleveland Metroparks using a modified version of Rosgen’s Bank Erosion Hazard Index (BEHI); this version consists of six metrics, none of which requires exact measurements. A field form was used to document the six metrics as follows: root depth as a percent in comparison to bank height, root density marked as a percent of the stream bank surface covered by plant roots, and surface protection described as the percentage of the stream bank covered by downed logs and branches, rocks placed along or imbedded in the bank, and bank material that is protecting the bank toe. Bank angle is determined by visual estimates for both right and left banks and bank materials can be described as bedrock, boulder, cobble, gravel, sand or clay; the last of which can be verified using a ribbon or ball test. The last metric is the observation of bank stratification; no layers, a single layer, or multiple layers accounting for the indication of erodible strata. Documentation of negative qualitative indicators included: unvegetated mid-channel bars, braided channels, leaning trees on both sides, exposed infrastructures, failed Best Management Products (BMP), headcuts, location downstream of a dam, exposed tree roots on both sides, slumping stream banks and perched tributaries. Once the data is calculated, interpreted, and mapped for sources of sediment pollution, the Cleveland Metroparks and NEORSD can implement restoration projects such as widening flood plains, native planting projects in riparian zones, conduct surface protection improvements to retain stream banks and ultimately, reduce sediment pollution within the Cuyahoga River.
Problem Statement
Sediment is one of the principle pollutants of surface waters of the United States and sediment eroded from stream bank failures has been found to be the single largest contributor to suspended sediment loads to streams draining unstable systems in the mid-continent (Simon et al., 2004). Further scientific research has indicated that increased sediment load affects water quality and the shape and dimension of river channels, thereby altering aquatic habitat and channel stability (Rosgen, 1993). A major factor that affects the sediment yields for the Cuyahoga River is bank erosion of tributaries which contributes to approximately 187,000 tons of sediment annually. In the summer of 2012, the Cleveland Metroparks, in partnership with the Northeast Ohio Regional Sewer District’s Stormwater Management Program, initiated a plan to assess stream bank erosion potential using a modified version of Rosgen’s Bank Erosion Hazard Index (BEHI) to locate sources of sediment pollution within the Cuyahoga River Watershed (CRW) and implement projects for restoration of stream banks to reduce sediment yields and pollution within the Cuyahoga River.
Hypothesis
If the modified Rosgen’s Bank Erosion Hazard Index (BEHI) is used to evaluate “Echo Mills,” a Class III primary headwater stream, and an additional unnamed Class II primary headwater stream located within the Cuyahoga River Watershed, then the “Echo Mills” stream will have, on average, higher BEHI scores based upon the composition of the stream bank material.
Purpose
The objective of this field study was to assess two primary headwater streams within the Cuyahoga River Watershed for stream bank erosion using a modified version of Rosgen’s Bank Erosion Hazard Index. The assessment is part of an ongoing project conducted in conjunction with the Cleveland Metroparks and the Northeast Ohio Regional Sewer District, to identify and map sources of sediment pollution, examine storm water management, and prioritize projects to retain and restore floodplains, riparian zones and stream banks to their natural disposition so as to reduce sediment loads within the Cuyahoga River Watershed.
Materials
Global Positioning System (GPS) Unit
Digital Camera
Waders/Boots
Bank Erosion Hazard Index Data Field Forms
Clipboard
Map of Stream Locations
Protractor
Procedures
Pre - Assessment Preparations
Meet with mentor at test site to obtain training for using GPS unit and instructions on how to implement the modified version of Rosgen’s Bank Erosion Hazard Index (BEHI).
Obtain field forms (100) and equipment required to conduct assessment.
Assessment Procedures
Travel to test site (Brecksville Reservation) utilizing maps citing location of Echo Mills, a class III, primary headwater stream.
Using GPS unit, mark location of test site and date on the field form ensuring the location within 10 meters of accuracy.
Estimate left and right bank height in meters and left and right bank length in meters.
Indicate stream bank material as one of the following: bedrock, boulder, cobble, gravel, sand, or clay.
Record root depth for the left and right bank as a ratio of the average plant root depth to the bank height expressed as a percent (e.g. roots extending 2’’ into 4’’ tall bank = 50 %.)
Determine root density by estimating the percent of stream bank surface covered by plant roots (e.g. a bank whose slope is half covered with roots = 50 %)
Estimate the percentage of the stream bank that is covered by plants, downed logs and branches, rocks along or imbedded in the bank, and slumped bank material and record as surface protection average.
Find the bank angle of the left and right banks and record approximate degree value for each.
Note and record the presence of erodible strata by stating no layers, a single layer, or multiple layers.
Estimate the distance of site from an existing infrastructure such as a road, bridge, culvert, utility, or pipe in measurement of 0-10 ft., 11-20 ft., 21-40 ft., 41-80 ft., or > 80ft.
Determine accessibility to site as by either walking or driving from a general public parking area in increments of: < 5 min., 5-10 min., 11-20 min., > 20 minutes.
Note and record the observance of any of the following negative qualitative indicators: unvegetated mid-channel bar, braided channel, leaning trees on both sides, exposed infrastructure, failed Best Management Projects (BMPs) downstream of a dam, head cuts, exposed tree roots on both sides, slumping stream banks, and perched tributaries.
Calculate data by scoring the left and right bank separately, adding up each value checked from each column together, then subtracting for any material or box that indicates to do so. The resulting total is the final, overall score for the test site.
Use digital camera to collect visual data; one image of left bank, one image of the right bank and one image downstream. If site exhibited one or more negative qualitative indicators, images should be taken to document their presence at the site.
Proceed downstream to next test site which is indicated by a change in bank curvature or a change in any one of the six metrics of plant root depth, plant root density, bank angle, surface protection, bank materials or bank stratification. Travels as far downstream as possible to obtain an accurate description of stream, for this research, 49 sites were assessed for the class III headwater stream.
Repeat procedures 1-15 for unnamed class III, primary headwater perennial stream. 38 sites were assessed for the class II headwater stream.
Graph results from field work.
Make conclusion and recommendations based on your results.
Data Analysis/Discussion
Streambank erosion is a natural process, but when accelerated due to urbanization and stormwater runoff, the effects of disproportionate sediment supply, stream channel instability, land loss, habitat loss and other adverse effects occur (United States Environmental Protection Agency, 2012). The field study conducted investigated Echo Mills, a Class III primary headwater stream and an unnamed Class II primary headwater stream; two tributaries of the Cuyahoga River located in the Brecksville Reservation of the Cleveland Metroparks for the potential for stream bank erosion. Streambank erosion can be traced to two major factors: stream bank characteristics (erodibility potential) and hydraulic/gravitational forces (Rosgen, 2001). In order to determine stream bank erosion potential, Rosgen’s modified Bank Erosion Hazard Index (BEHI) was employed to focus on the stream bank characteristics of bank height and angle, bank material, percentage of root depth and density, surface protection, and stratification; allowing the BEHI to be a useful tool in identifying actively eroding locations or hot spots and aid in stormwater management and restoration practices.
The modified version of Rosgen’s BEHI does not require measurements so the variables of bank height and angle are estimated, facilitating the rapid assessment method for stream bank erosion. The bank angle is found in degrees by viewing the bank toe (the waterline) to the top of the bank. The left and right banks are assessed separately due to the meander patterns of the streams; one bank naturally tends to higher than the other, therefore, their scores for bank angle will differ. In general, steeper banks tend to be more erodible than less steep banks. Bank angles greater than 90 degrees occur on undercut banks (Rathbun, 2011). Undercut banks hang over the stream and tend to provide a stable habitat for macroinvertebrates and fish, however, if seriously undercut, it may be vulnerable to collapse. Steeply sloping banks (30 degrees or more), tend to be highly prone to erosion while gradual sloping banks are more resistant to erosion but do not provide much streamside cover (USEPA, 2003). Specific sites that demonstrated undercut banks include, but are not limited to sites 24, 27, 28, 39L, 48L, 54L, 85, 90L, and 91. The modified BEHI used for this study subdivides the bank angle from 0 to 20 degrees, 21 to 60 degrees, 61 to 80 degrees, 81 to 90 degrees, 91 to 119 and any bank angle greater than 119 degrees. Given these divisions, the stream banks assessed for this study recorded 48.7% at 0-20 degrees, 16% at 21-60 degrees, 12.2% at 61-80 degrees, 18.6% at 81-90 degrees, 4.5% at 91-119 degrees, with no bank angles above 119 degrees. Based on the above information from the USEPA, 51.3% of the stream banks assessed indicated a higher potential for erosion when only factoring bank angle.
The composition of a stream bank plays a large role in determining its erosion potential; large materials like boulders or very cohesive materials like clay can lower erosion risk, while small noncohesive sands can be very erodible (Rathbun, 2011). Material types are classified by size and erodibility ranging from boulders which are larger than 255mm, cobble measured from 65 to 255mm, gravel sized from 2 to 64mm, sand grains smaller than 2mm; bedrock and clay are not sized due to their being substances that are very cohesive and erode slowly. When assessing the stream banks of Echo Mills (labeled Stream 1), 24 out of 84 sites (28.6%) indicated the presence of cobble, 10 out 84 sites (11.9%) were gravel based and 50 out of 84 sites (59.5%) were sand material. The BEHI employs a scoring system that adjusts for bank material; when sand is present, 10 points are added to the total, often causing the stream bank rating for Stream 1 to be elevated into a High (41.8%) or Very High (21.4%) category for the potential for erosion to occur. The stream bank assessment for the unnamed Class II stream (labeled Stream 2) evidenced that 2 out of 72 sites (2.8%) were bedrock, 13 out of 72 sites (18.1%) displayed boulder material, 35 out of 72 sites (48.6%) were composed of cobble, 10 out of 72 sites (13.9%) were gravel based, 6 out of 72 sites (8.3%) were sand material and 6 out of 72 sites (8.3%) consisted of clay. Due to the fact that 50 out of the 72 sites displayed bank materials that were highly cohesive and not prone to erosion, 59.7% of the sites on Stream 2 were labeled Very Low and 12.5% scored within the Low category on the BEHI, thus Stream 2 would be considered as a low risk for erosion to occur. The data indicates, according to the BEHI, that Stream 1 displays numerous sites that show the potential for erosion due to presence of sand and would tend to transport sediment downstream during a stormwater event due to particle shearing and toe erosion when the velocity and up-welling currents are accelerated. Possible scenarios for further investigation of Stream 1 sites may include placing bank pins into both banks and the streambed at various locations throughout the stream and obtain measurements on an annual basis to determine how quickly each site is eroding. Once more extensive data is collected, decisions can be made on how to retain and restore the stream bank; plans could include planting root dense vegetation or adding more cohesive material to the bank to slow down the erosion process.
When discussing the results of the fieldwork in regards to bank material with Ms. Jen Grieser, Manager of the Division of Natural Resources for the Cleveland Metroparks, she stated that one of the sites she would investigate further would be site 98R on Stream 2. The site noted clay as its major bank material but if the clay were eroding, pollutants such as metals and toxic organic material could adhere to the clay sediment that, once the material is deposited within the Cuyahoga River, would need to be dredged and disposed of, increasing costs for maintenance of the river. In addition, when the clay particles are suspended, they increase turbidity and harm aquatic organisms, therefore, making this site a candidate for restoration.
After determining the composition of the bank material, the next step in the process for determining if a site would require restoration would be to estimate root depth and density. The importance of the vegetation component in regard to stream bank erosion is demonstrated by the fact that soil is generally strong in compression, but weak in tension. The fibrous roots of trees and herbaceous species are strong in tension, but weak in compression. Root-permeated soil, therefore, makes up a composite material that has enhanced strength (Thorne, 1990). Previous fieldwork studies have shown that the majority of fine roots contribute to the reinforced root-soil matrix (Simon and Collison, 2002; Pollen et al., 2004). When using the BEHI for root depth and density, the researcher notes the presence and type of vegetation which occupies the top layer of the stream bank; if grasses are the dominant growth, root depth is minimal, if trees are abundant, then root depth is scored at a higher percentage. At this time, the researcher also documents qualitative indicators regarding plant growth by observing the presence of unvegetated mid-channel bars, leaning trees on both banks, and exposed tree roots on both banks. If a site proves a high exposure of roots and leaning trees, restoration practices would require the stream bank to be modified by excavating the site to create “benches” in the bank to widen the floodplain; it would not however, add soil to the site, due to the lack of compression of the new substrate that in turn, would only erode easily after placement. Sites that displayed qualitative indicators of leaning trees and/or exposed tree roots include, but are not limited to sites 24, 29, 30, 31, 35, 36, 38, 44, 50, 57, 60, 78, 82, 83, 93, and 114.
Surface protection refers to the percentage of the stream bank covered by plants, downed logs and branches, rocks placed along or imbedded in the bank, and slumped bank material that is protecting the bank toe (Rathbun, 2011). When a stream bank displays signs of erosion, often, restoration projects will employ Best Management Products (BMP) which can include large, plastic, coiled tubing that is designed to be imbedded in the stream bank to hold the material in place. When flooding occurs, BMP’s can sometimes become dislodged and need to be replaced; a failed BMP was documented at Site 85 and was reported to the proper agency for repair. Other artificial bank modifications include all artificial structural changes to the stream bank such as riprap (broken rock, cobbles, or boulders placed on earth surfaces such as the face of a dam or the bank of a stream, for protection against the action of the water) and bulkheads (USEPA, 2003). Natural surface protection of downed logs was documented at sites 38, 39, 40R, 48L, 55L, 57L, 63L, 73L, 81L, 84L, 96R, and 96L.
The final metric on the BEHI is bank stratification. This factor is valuable because some stream banks contain layers, or strata, of more erodible materials like sand, and these unstable layers can increase the erodibility of the entire bank (Rathbun, 2011). The varying soils and textures can erode at different rates creating undercuts and headcuts within the stream. The BEHI scoring system adds 5 points to the assessment when one layer of stratification is present and 10 points when multiple layers are exposed. When analyzing the data, both streams recorded single layer stratification; one site on Stream 1 (Site 68), and a portion of Stream 2, (Sites 82 through 85, 90L, and 98) thereby elevating of the BEHI scores for these locations into the High or Very High category for erosion potential.
When the assessment was complete, eighty-four sites were assessed on “Echo Mills” with fifty-three sites (63%) recording scores for high or very high potential for erosion. Seventy-two sites on the Class II stream were assessed with twelve sites (16.7%) recording scores for high or very high potential for erosion. The BEHI emphasizes the importance of streambank materials, often elevating sites into the high or very high range based on the presence of highly erodible, non-cohesive materials such as gravel and sand. Results suggest that “Echo Mills” evidenced higher erosion potential overall than the unnamed stream when considering that approximately 60% of the “Echo Mills” sites recorded sand as the dominant bank composite, whereas 8.3% of the unnamed stream sites were comprised of sand, causing it to be less susceptible to potential erosion.
In summary, the modified BEHI is a useful tool to provide a rapid inventory to assist in channel stability evaluation, assess priorities for restoration and provide information for riparian habitat management recommendations (Rosgen, 2001). This quantitative assessment can also provide the means to determine potential sediment supply into a river system or watershed caused by stream bank erosion thereby completing the first step in developing measures to reduce sediment loads for a particular water source.
Final Conclusion
Water is a natural agent for erosion and it will choose the path of least resistance as it meanders, carrying soil and material to be deposited along its path, once hydraulic and gravitational forces change. The degree to which a streambank will erode is factored not only by the velocity and flow mechanics of the water but also by the streambank characteristics of bank height and angle, root depth and density, surface protection and bank material composition. My original hypothesis stated that “Echo Mills,” a Class III primary headwater stream (Stream 1) would evidence, on average, a higher BEHI score, as compared to an unnamed Class II headwater stream (Stream 2), both of which were located within the Brecksville Reservation of the Cleveland Metroparks, approximately one mile apart, due to the composition of its bank material. Stream 1 did prove higher erosion potential than Stream 2 based on the data collected; approximately 60% of the sites recorded sand, a highly non-cohesive and erodible material, as the dominant bank composite, whereas only 8.3% of Stream 2 sites were comprised of sand, causing it to be less susceptible to the factors of erosion. The purpose of this study was to assess two primary headwater streams as part of an ongoing project to map sources of sediment pollution, identify erosion “hot spots” and aid in prioritizing restoration projects to control stormwater runoff and reduce watershed sediment loads; this objective was achieved through the field study utilizing the six metrics of the BEHI and documentation of qualitative indicators for stream bank erosion potential. The assessment is only the first step in the process of addressing the problems of stream bank erosion, but it provides a starting point for watershed planning and floodplain management projects designed to retain and restore the stream banks throughout the Northeast Ohio Region.
 
River 1 Analysis
River 2 Analysis
 
 
Credits
Thank you…
Mr. Jennrich, for time, advice, inspiration, support and his signature.
Ms. Jenn Greisler., Manager of Natural Resources for the Cleveland Metroparks, for taking time for educating me about the Cuyahoga River Watershed and supplying me maps of the river and training in the BEHI method.
To my mother, for helping me put together this project the correct way, I would have done it completely wrong without you! Thanks for photographing the pictures for my project.
Mrs. Rossman, my 8th grade science teacher, for teaching me how to do a science project and for opening the IWA science fair to alumni.
To my father, my computer tech, and for giving me a new perspective on the “look” of my board. Thanks for photographing the pictures for my project.
Scientists in past years, for having such great work to get information from; I am glad that I was able to see so many excellent reports. I hope that this project can help others in the future.
References
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