Physical Channel Assessment

Transcription

1 Poplar River Turbidity Assessment March 14, 2008 Physical Channel Assessment

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3 Poplar River Turbidity Total Maximum Daily Load Physical Channel Assessment Task Order No Prepared for: U.S. Environmental Protection Agency Region 5 77 West Jackson Boulevard Chicago, IL Prepared by: RTI International 3040 Cornwallis Road Research Triangle Park, NC USEPA Contract Number 68-C February 25, 2008

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5 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 2 of 24 ACKNOWLEDGMENTS Dr. Joe Magner (Minnesota Pollution Control Agency) provided essential direction and guidance throughout the process including the field reconnaissance. Special thanks are due to Ms. Julianne Socha, Project Officer-EPA, for her support with administrative aspects of this grant funded project. Several other experts contributed their time, efforts, and talent toward the preparation of this report. The Project Team acknowledges the contributions of each of the following and thanks them for their efforts: Mr. Tom Schaub (MPCA) for input during the preliminary field trip and coordination efforts in the early stages. Ms. Karen Evens (MPCA) for providing data and coordinating the communication between the team and MPCA. Mr. Clint Little (Minnesota Department of Natural Resources) for supplying essential information, particularly the aerial photographs. Ms. Debra Taylor (U.S. Environmental Agency Duluth) for data sets on North Shore summary. RTI Project Team: Dr. Bill Cooter, RTI International Raleigh, North Carolina Mr. Doug Bach, SEH Inc. Madison, Wisconsin Mr. Brian Jacobson, URS Corporation Raleigh, North Carolina Mr. Troy Naperala, URS Corporation Traverse City, Michigan Mr. Dan Cazanacli, SEH Inc. Minneapolis, Minnesota (Project Manager) Dr. Sanjiv Sinha, Environmental Consulting & Technology (ECT) Inc. Ann Arbor, Michigan (Project Director)

6 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 3 of 24 Table of Contents 1 EXECUTIVE SUMMARY PROJECT INTRODUCTION: STUDY AREA AND FIELD RECONNAISSANCE General Characteristics Field Reconnaissance CHANNEL DESCRIPTION General Stream Characteristics Flow Depth and Width Stream Valley and Channel Mobility Erosion Processes within the Channel Banks and Valley Walls STREAM SEDIMENT AND ITS TRANSPORT In-Stream Sediment Suspended Sediment Size and Turbidity within Lower Poplar River Possible Evidence of Increased Sediment Influx in Lower Poplar River SUSPENDED SEDIMENT WITHIN LOWER POPLAR RIVER: SOURCES AND ANNUAL ESTIMATES Sources and Processes Impacting the Amount of in Lower Poplar River Estimating the Amount of Stream Related Suspended Sediment within Lower Poplar River CONCLUSIONS REFERENCES APPENDICES List of Tables Table 1. Estimates of Annual Average Suspended Sediment...12 List of Appendices Appendix A Maps of Study Area and Field Notes Appendix B Field Photographs

7 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 4 of 24 1 Executive Summary A physical channel assessment was conducted to evaluate sources of localized soil erosion along the Lower Poplar River. There were three primary purposes to this assessment, namely: a) classifying the river to the extent possible, b) identifying the primary sources and processes responsible for suspended sediment in the system, and c) quantifying the input of suspended sediment from each of these sources and processes. The evaluation presented here-in is expected to be preliminary for two reasons, namely: a) this report is part of a larger initiative to establish a turbidity Total Maximum Daily Load (TMDL) for the sub-watershed that looked at many parameters as well, and b) limited resources were assigned for the field assessment. The field reconnaissance included observations, cross section measurements and other data collections. It was found the Lower Poplar River shares many characteristics with mountain streams. Its longitudinal profile does not exhibit a gradual downstream decrease in slope, typical of most streams. It is rather flat or slightly convex-up. A channel-reach classification of mountain streams developed by Montgomery and Buffington (1997) was used to characterize the stream. Four channel reach types (bedrock, cascade, plane-bed, and step-pool) were identified. Most of the channel exhibits a morphology that is between the step-pool type and plane-bed type. The bed surface is covered (armored) by gravel to boulder size material. Larger, boulder-size particles, protruding above the base flow water levels are ubiquitous throughout the channel. Due to the irregular bed surface the local depth typically varies from several inches to approximately two feet during base flow conditions. Pools have a maximum depth of three to four feet. Typically the width of the channel ranges between 35 to 45 feet. The channel lacks a well defined floodplain and, for the most part, is confined by the topography of the valley. In places, the bottom of the valley is sufficiently wide and flat, and the channel displays entrenched meanders and lateral mobility. Historical aerial photographs indicate changes in channel position. One example is the meander loop at the Megaslump site which has shifted over 200 feet. The banks are armored by irregular ribbons of cobble to boulder material and there is little evidence of on-going channel bank erosion. Dense vegetation dominated by trees and brushes, covers the surface above the rock-armored sides with no well defined banks. The bank stability analysis discussed in the QAPP, using Bank Stability and Toe Erosion Model, is not applicable and was not performed. The channel bed is dominated by poorly sorted large (coarse gravel to boulders) particles and only a small proportion of finer sediment is found trapped in the spaces between larger particles. In most places, only ten to twenty percent of larger particles are buried into the finer sediment. Due to the stream s high energy, there are no good geomorphic indicators

8 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 5 of 24 that would reflect an increased flux of fine sediment as described by Montgomery and MacDonald (2002). Certain places such as the Megaslump were documented to have a higher proportion of fine sediment in and near the streambed. Six types of localized sediment sources were observed and are discussed in this document: channel bed incision and stream lateral migration are found to not be a significant source of fine sediment. However, when these processes occur in the vicinity of the valley slopes, they can be a factor in the formation and expansion of landslides which in turn can mobilize a large amount of fine, suspended sediment from the walls of the valley. The erosion associated with a sudden channel migration such as meander cut-offs can mobilize significant amount of material, including some fine, suspended sediment but their effect is rather short lasting. Other potential sources of suspended sediment are within the river valley and not directly related to stream activity. The erosion ravines formed at points of concentrated runoff are an important source of suspended sediment. Finally, the recreational development appears to have resulted in a multitude of surfaces that are vulnerable to erosion. These include ski trails, ATV trails, hiking trails, utilities, road surfaces, road embankments, and roadside ditches. The report is organized as follows: Chapter 2 outlines the general characteristics of the watershed. Description of the channel can be found in Chapter 3. A section on stream sediment and its transport is outlined in Chapter 4. Chapter 5 discusses the sources of sediment in the Lower Poplar River, and attempts to develop an estimate of their contributions. Finally, Chapter 6 presents the conclusions of this investigation.

9 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 6 of 24 2 Project Introduction: Study Area and Field Reconnaissance The goal of this physical channel assessment study was to better understand the evolution, the present condition, and sources of turbidity within the Lower Poplar River. Analysis of existing turbidity and other water quality parameters in the Poplar River revealed a strong correlation between turbidity and total suspended solids (RTI 2007). The causes of increased suspended sediment concentrations, whether episodic, temporary, or long term, can be multiple and related to different erosion processes. The physical channel assessment is aimed at estimating the stream related erosion areas and the relative contribution of suspended sediment from each major source. Field observations and measurements were focused on the stream itself, defined as the area of active flow (the streambed and the stream banks) and the stream valley, a much larger (i.e., wider and deeper) feature that evolved over geological time as a result of streambed incision and subsequent erosion caused mainly by landslides. 2.1 General Characteristics The Poplar River is one of the many streams on the North Shore of Lake Superior. Most of these streams are relatively short and steep and have a steeper gradient in the lower watershed than in the upper watershed (Fitzpatrick et al, 2007). This is due to the bedrock topography and the adjacent terrain that was shaped by the last advance and retreat of icesheets. A ridge of Precambrian volcanic rocks, mostly basalts, parallels the Minnesota shoreline of Lake Superior. The bedrock within the watershed of the Lower Poplar River is relatively shallow and exposed in several places. The last glacial period, called Wisconsinian (10,000 to 70,000 years ago), left behind thin drift of ground moraine deposits. The upper watershed of the Poplar River is located on an elevated plateau. The typical elevation in the upper watershed is about 1300 feet and the average stream gradient is less than 1 percent. The channel is relatively wide (100 feet or more) and characterized by wide meanders. Dense vegetation consisting of willows, reeds, and other hydrophilic grasses buffer the banks which show little signs of erosion. Impressive falls (rapids), approximately 150 feet high, mark the transition from the upper watershed to the lower watershed. By contrast, the lower watershed, which is the topic of this assessment, is characterized by a much steeper gradient and narrower width. For the purposes of this report, the Lower Poplar River will describe the watershed area downstream of the Superior Hiking Trail Bridge (Study Area Map).

10 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 7 of Field Reconnaissance A field reconnaissance was performed between July 2 and July 6 of The scope of the reconnaissance included field observations and measurements at fourteen locations (see Appendix A). Photographs, soil or substrate characteristics, vegetation cover and other observations were collected at these sites. The chosen locations were scattered and covered all portions of the lower stream (upstream, middle, and downstream). In addition, width and depth measurements as well as photographs were taken at all bridge crossings and other access locations. At six of the locations, cross-sectional surveys and more detailed observations were performed (Study Area Map, Figures 1, 2, and 3). The grain size distribution was found to be bi-modal (i.e., a combination of very coarse material such as boulders and cobble, and finer sediment trapped between larger particles). Therefore, a precise determination of the median particle size (D50) was deemed to be of little use. Some visual observation and limited measurements of the stream valley sides were also made. All areas displaying visible signs of erosion were photo-documented. The large landslide area referred to as the Megaslump (Figure 2) and, several other smaller landslides and a major erosion ravine were identified in the upper portion of the lower watershed. Study Area Map and Figures 1, 2, and 3 indicate the locations of the cross sections, landslides and other important features that were documented as part of the field reconnaissance. The field notes, cross-sections and a longitudinal profile are presented in Appendix A. Photographs are appended in Appendix B.

11 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 8 of 24 3 Channel Description 3.1 General Stream Characteristics The Lower Poplar River has more in common with mountain streams than with the typical lowland streams of the Midwest. Like many of the mountain streams, the Lower Poplar River does not fall into a general category of braided or meandering streams. Braided streams are characterized by channel bars and flow splits, a result of intense sediment deposition. Typical meandering streams evolve as a result of the flow interaction between the channel and the adjacent floodplain; an interaction defined by continuous channel lateral shifting and overbank deposition. Neither process is typical of the Lower Poplar River. Furthermore, the longitudinal profile does not exhibit a typical concave-up shape commonly referred to as a graded profile (i.e., the longitudinal bed slope is steeper upstream and gradually milder downstream). A sharp change in bed elevation is noticeable near the mouth where a succession of falls is present (upstream and downstream of Highway 61). Upstream from these falls, the average longitudinal slope is approximately 0.03 (3 percent) and the general shape of the profile is rather flat or slightly convex-up (see Appendix A). Such longitudinal shapes are common in cases of relatively young rivers developed in glacial valley. Ellen Wohl, in a comprehensive review of mountain rivers (2000), noted that Mountain river channels are less likely than low-gradient alluvial channels to approximate the graded longitudinal profile and progressive downstream changes in channel morphology that are commonly regarded as the stable conditions toward which rivers trend. Because of the relative lack of consistent downstream trends, mountain rivers are most appropriately classified at reach scale. Essentially this means that the characteristics of these rivers may change somewhat irregularly from one portion to another. Following this idea, it seems more fitting to use the process based channelreach classification of mountain streams of Montgomery and Buffington (1997). The authors identify seven types of channel reaches that are commonly encountered in mountain drainage basins: bedrock, cascade, step-pool, plane-bed, pool-riffle, dune-ripple, and colluvial. These channel reach types can be found in progression in many of the mountain streams. In the case of the Lower Poplar River, four of these channel reach types, namely bedrock, cascade, plane-bed, and step-pool were identified. An explanation of each of these four channel reaches follows. Bedrock reach is a special channel type in a sense that it displays little to no alluvial material. The channel is incised into bedrock and confined by steep valley walls. The channel geometry and the position of the bed are controlled by the rate of incision. Two significant bedrock outcrops were identified along the Lower Poplar River. One is a succession of falls approximately 500 feet to 1500 feet upstream from the mouth extending south and north of Highway 61. The other one is a reach located approximately a mile

12 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 9 of 24 from the mouth, on the north edge of the golf course (Study Area Map - Appendix A; Photo 11 Appendix B). The cascade type is only present in the upstream part where the steep channel bed is confined within a relatively narrow valley. In cascade type reaches, the flow tumbles over large boulders that dominate the channel bed. The size of the boulders exceeds the depth of the flow several times. The step-pool and plane-bed types are by far the most common channel-reach types along the Lower Poplar River. Overall, the channel exhibits a morphology that is between the step-pool type and plane-bed type. The step-pool type (Photo 10 Appendix B) is defined as a rhythmic sequence of drops followed by a scour pool. Only the upstream part shows regularity in terms of spacing with steps spaced a fraction of the channel width apart. The remainder of the river shows little regularity in terms of steps distribution. Most of the pools are relatively shallow (less than 3 feet deep). The plane-bed term is also applied to streams with sandy bottoms which could possibly lead to confusion. In their classification of mountain streams, Montgomery and Buffington (1997) use this term to describe streams with much coarser (gravel to boulder) material. This definition is also applicable to the Lower Poplar River where the bed surface is covered (armored) by gravel to boulder size material (Photo 9 Appendix B). Larger, boulder-size particles, protruding above the normal water levels are ubiquitous throughout the channel. The coarse material is colluvial in origin, meaning that it is detached from the valley walls and transported downhill by gravity (i.e., in conjunction with sloughs or landslides). Examination of the valley walls in places that lack vegetation cover (i.e., landslides) shows a poorly sorted mixture of boulders and cobbles encased in a matrix of finer sandy and silty material (Photo 13 Appendix B). This mix is typical of glacial deposits. The size range and composition of the cobbles and boulders observed along the valley walls matches those of the coarse material observed within the stream. 3.2 Flow Depth and Width The ubiquitous nature of boulder particles, many of which protrude above the water surface, translates into irregular shape cross-sections making the flow depth measurements difficult. On average, the typical base flow depth is slightly over one foot (Appendix A Cross Sections). Within a given cross-section, the local depth typically varies from several inches to approximately two feet. Narrow portions of the channel and infrequent pools may show a maximum depth of three to four feet. The only place where a deeper pool is present is near the mouth, downstream of Highway 61.

13 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 10 of 24 Simple flow computations indicate that, on average, during high flow periods, which typically occur late in the spring and are caused by snow melt, the water levels could be 1 to 3 feet higher than the normal flow conditions observed during the field reconnaissance. During base flow conditions, the flow width of the Lower Poplar River varies from 30 to 60 feet with the majority of the measurements falling within 35 to 45 feet range. The coarsest streambed material ranges from large blocks (5 to 10 feet) at the upstream end to boulders and cobble (0.5 to 2 feet) in the downstream part (Appendix B Photos). 3.3 Stream Valley and Channel Mobility The Lower Poplar River flows through a valley that is approximately 120 to 250 feet deep and 500 to 1000 feet wide. The average side slopes of the valley (where many of the ski trails are located) vary between 10 and 25 degrees (18% to 50%). The bottom part of the valley is, however, less steep and varies in width from 100 to 400 feet (Appendix A Study Area Map). The channel lacks a well defined floodplain and, for the most part, is confined by the topography of the valley. In some places, one side of the channel is flanked directly by the valley slopes. In other places, however, the bottom of the valley is sufficiently wide and flat and it could be looked upon as a narrow floodplain. The channel displays some lateral mobility and several entrenched meanders have developed as a result. Entrenched meanders develop in places where floodplains are relatively narrow and their surface slope towards the channel (i.e., as opposed to wide and flat floodplains that allow for highly sinuous meanders to form). Examination of historical aerial photographs indicates some changes in channel position, most notably in the upstream part. Aerial photographs from 2003 compared against aerial photographs from 1934 reveal that a major meander loop, where the Megaslump is located, migrated south-southeast by approximately 220 feet (Appendix A Figure 2). Other major changes are a smaller meander migration further upstream in the ski hills area, and a couple of meander cut-offs, located within the downstream portion, approximately half a mile from the mouth (Appendix A Figure 1). The field reconnaissance documented several remnants of abandoned streambeds. The segments that have been abandoned were filled with relatively well sorted cobble and their surface is above the surface of the present channel bed. This suggests that the channel migration took place in conjunction with channel incision. Unlike the meanders of low-gradient alluvial streams with wide floodplains, the Lower Poplar River s meanders are entrenched and well confined within the valley.

14 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 11 of Erosion Processes within the Channel Banks and Valley Walls The sides of the active flow area are armored by irregular ribbons of coarse size (cobble to boulder) of densely packed rock material. As the erosion of the valley progressed, the bulk of the finer material has been transported downstream, while the boulder and cobble size particles have been retained within the channel stabilizing its sides and bottom. Thus, the erosion and selective transport processes resulted in a self-armoring mechanism. There is very little evidence in terms of on-going channel bank erosion (Appendix B Photos 8, 9, 10, 11). Erosion is visible, however, in places where the bank and the valley wall form a continuous slope surface, most notably in the Megaslump area where the channel is adjacent to the sloped surface of this major landslide (Appendix B Photo 14). This and other landslides are a different form of erosion from what it typically referred to as stream bank erosion. The distinction between stream bank erosion and valley wall erosion is not simply semantic. Stream bank erosion typically implies a local and limited slope failure often aided by the collapse of trees. It is a common occurrence along alluvial channels which tend to have well defined banks with a top surface that is periodically flooded. Thus, the vertical extension of the stream bank erosion surface is limited. By contrast, the landslides documented along the Lower Poplar River extend vertically for tens of feet, well above highest flooding levels. The likely mechanism that triggers the formation of these landslides is the erosion of the slope toe due to channel incision and lateral migration. The same processes are also likely to cause an expansion of the landslide area. On average, the rock-armored sides of the channel extend 1 to 2 feet vertically and 5 to 20 feet laterally. Dense vegetation dominated by trees and brushes, covers the surface above the rock-armored sides. These vegetated surfaces are less steep but for the most part, there is no clearly identifiable top of the bank. In many places the side slopes of the channel and the adjacent slopes form a continuum with little or no slope inflection. Therefore, the geometric dimensions of the channel banks cannot be easily defined. The bankfull depth, a popular geometric dimension employed in the characterization of self-formed alluvial channels with well defined floodplains, is neither identifiable nor relevant in the case of the Lower Poplar River since, for the most part, the channel does not exhibit well defined banks. For these reasons, the type-bank stability analysis discussed in the QAPP, using Bank Stability and Toe Erosion Model, is not applicable and therefore was not performed.

15 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 12 of 24 4 Stream Sediment and its Transport 4.1 In-Stream Sediment As mentioned above, the channel bed is dominated by poorly sorted large (coarse gravel to boulders) particles. The largest of these particles are irregularly spread across the channel and, during base-flow conditions, protrude above the surface of the water. A small proportion of finer sediment, mostly coarse-sand to fine-gravel in size, is found trapped in the spaces between larger particles. Another way to define this spatial relationship is to look at the larger particles as being superficially buried into the finer sediment. The degree to which the larger particles are buried into the finer sediment is referred to as embeddedness. Quantitative embeddedness measurements are labor intensive, time consuming and logistically difficult to execute in a rapid flowing stream. In Lower Poplar River, based on visual observation, in most places, only 10 to 20 percent of the volume of the cobbles and boulders is buried into the finer sand to gravel sediment bed. This ratio applies both to the streambed and the stream banks. The coarse cobble-size material can only be entrained and rolled downstream during high flow conditions. The larger, boulder-size particles are not likely to be entrained at all, except during extremely large flows. The stream has more than adequate energy (competence) to transport the sand-sized and finer particles during normal flow conditions. The transport of fine material is essentially supply-limited. In other words, the stream can transport all of the sand-sized, and any finer material reaching the channel. The transport of fine material is essentially supply-limited. In other words, the stream can transport all of the sand-sized, and any finer material reaching the channel. The presence of finer material within the bed and along banks is due to trapping between much larger particles. Placed between much larger particles, the smaller sand-sized particles are essentially sheltered from the drag force imposed by the flow, a process referred to as the hiding effect. During increased flow conditions, the increased drag force and small scale turbulence may entrain a small fraction of the sand-sized sediment that is trapped between the larger particles. More sand is likely to be entrained during the spring high flows when some of the large cobble-size particles that shelter the fine sediment are mobilized as well. Thus, the channel itself is not a source or a repository of fine sediment. The fine sediment is limited in supply and periodically flushed out. 4.2 Suspended Sediment Size and Turbidity within Lower Poplar River One of the main questions to be addressed as part of the overall TMDL process is whether and how the channel processes may impact the level of turbidity. The exact size

16 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 13 of 24 distribution of the suspended sediment that results in elevated levels of turbidity is not known. However, it is reasonable to assume that the bulk of the suspended sediment responsible for the turbidity levels falls within silt and clay size range. This is similar to a limited set of suspended sediment grain size data for the Baptism River available from the USGS that indicates, on average, silt size and clay size sediment make up 85% of the total suspended load. The Baptism River is located southwest from the Poplar River and has similar characteristics. Based on visual observations within the lower Poplar River watershed the bulk of the fine sediment found along the Lower Poplar River channel bed and banks is coarser, falling in the range of medium size sand to fine gravel with a very small proportion of silt and clay particles. Substrate particle size data from other North Shore streams with gravel to boulder beds indicate the proportion of clay, silt, and fine sand is in the substrate is less than 2 percent (US EPA). All this information indicates that the channel itself is not a significant source of fine (i.e., mostly clay and silt size) suspended sediment that would in turn result in elevated turbidity levels. 4.3 Possible Evidence of Increased Sediment Influx in Lower Poplar River Montgomery and MacDonald (2002) provide a summary of the stream characteristics that are indicative of a chronic increase in the supply of fine sediment (i.e., particles smaller than 2 mm). These characteristics include channel dimensions, bed material, pool characteristics, reach morphology, and sediment transport (suspended load and bed load). Documenting changes in these characteristics implies measurements performed at different moments in time. Unfortunately, no previous detailed investigation is available in case of the Lower Poplar River. According to Montgomery and MacDonald, the cascade and steppool reach types show only limited changes in these characteristics when the supply of fine sediment increases. The plane-bed reach type would respond to a chronic increase in fine sediment by displaying an increase in fine sediment in the bed material and increased embeddedness. Because of the high energy flow, an increase in fine sediment proportion along the entire channel is not to be expected. Unless trapped between larger particles all fine sediment is eventually carried downstream. Certain places, however, were documented to have a higher proportion of fine sediments and a higher embeddedness. These places include the Megaslump (Appendix B Photo 15), another landslide located further upstream, and a large size erosion ravine discussed below (Appendix B Photo 30).

17 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 14 of 24 5 Suspended Sediment within Lower Poplar River: Sources and Annual Estimates 5.1 Sources and Processes Impacting the Amount of Suspended Sediment in Lower Poplar River In general, the potential localized sources of suspended sediment in the Lower Poplar River watershed include: Channel bed incision Sudden channel migration (e.g., meander cut-off, channel avulsion, etc) Streambank erosion Landslides (slumps) near active channel Incision along valley slopes (erosion gullies and ravines) Localized erosion within the river valley related to land-use alteration The more uniform, watershed-wide erosion due to detachment of soil particles is analyzed separately and is not included in this report. The first three sediment sources listed above are directly related to the stream and stream processes. The fourth source refers to sediment detached from the valley walls but, the stream processes, streambed incision and lateral migration specifically, may play a role in triggering and enlarging these landslides. The last two possible sources are located within the valley sides and are largely independent of the processes within the main stream. The assessment of sediment sources is further complicated when potential anthropogenic factors may exist. The current human factor is not likely to significantly impact the stream erosion rates in the area of active flow (i.e. streambed incision or channel lateral migration). However, land use practices, such as recreational development, may have contributed to: a) expansion of landslide areas, b) formation of erosion and ravines gullies on the valley sides through creation of concentrated flow routes, and c) larger than normal sediment erosion rates within the watershed due to changes in land-use resulting from removal or degradation of the vegetation cover. Individual sources and processes of suspended sediment are discussed in further detail below: Channel Bed Incision Channel incision is an ongoing geological process which characterizes all high-gradient North Shore streams flowing into Lake Superior. These streams continue to cut down in the glacial till material, slowly adjusting the shape and slope of the longitudinal profile.

18 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 15 of 24 This process, however, takes place at a relatively slow rate and, on an annual basis, will not result in the mobilization of significant amounts of suspended sediment from the streambed. While the channel bed itself is not a significant source of suspended sediment, channel incision may play a role in the occurrence of landslides observed in the vicinity of the channel. Channel bed incision may occur simultaneously with the gradual streambank migration discussed below. Sudden Channel Migration (e.g. Meander Cut-Off) Aerial photographs taken in 1934, 1991, and 2003 suggests that rapid lateral migration has taken place at certain locations. The meander cut-offs and channel diversions have likely entrained a significant amount of sediment including a suspended load fraction. However, these kinds of sudden channel migrations are one-time events associated with abnormally high flow rates. Most of the suspended load that would have been generated this way was dispersed throughout the stream and flushed out of the system. Empirical evidence and laboratory study indicate that pulses of fine sediment in streams are dispersed rather fast (Cui et al., 2003). Streambank Erosion (Gradual Channel Migration) Stream bank erosion implies gradual channel migration, as opposed to major sudden changes, such as channel avulsions or meander cut-offs, which are one time processes associated with extreme flow events. Generally speaking, stream bank erosion in alluvial streams could greatly increase the amount of suspended load due to the local degradation and collapse of the banks. However, in the case of the Lower Poplar River the banks are armored with large size particles and there is little evidence of active, on-going bank erosion. Another aspect that deserves attention is the erosion associated with large falling trees. When a tree tilts toward the channel and ultimately falls down, the root system dislodges sediment from the bank. A qualitative visual assessment suggests that the large falling trees as well as the large woody debris are rather infrequent. On average, one major falling tree was observed every several hundred feet. Except for historic logging Landslides Near Active Channel In places where the active channel is near the valley wall, landslides are likely to form and/or become larger as the channel shifts laterally. Such places, most notably the meander bend at the Megaslump, could be considered the equivalent of the gradual streambank erosion except that it is the slope of the valley that is being eroded and not the streambank (Appendix A Figure 2).

19 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 16 of 24 Several landslides have been documented along the channel. The Megaslump, is much larger in size and its total surface area may exceed the surface area of all the other landslides combined (Appendix A Study Area Map). The Megaslump is located on the eastern bank approximately 1½ miles upstream from the mouth. At this location, the channel forms a relatively tight meander that could be tracked on the aerial photography from 1934 which also shows what appears to be a landslide of considerably smaller size. Since then, the meander appears to have shifted approximately 220 feet in a southsoutheast direction, impinging upon the relatively steep side of the valley. Presently, the stream flows adjacent to the slope failure area which is approximately 50 feet high. Water discharge from the nearby water treatment ponds may have contributed to the expansion of the exposed failure surface. Erosion of the Megaslump will be minimal if the discharge operates as designed; however, if the flexible discharge pipe were to become detached during discharge event significant erosion would occur. Several gullies dissect the face of the landslide and the unvegetated soil surface appears to be highly erodible (Appendix B Photo 13). Given its size and proximity to the channel, the Megaslump area is a likely major source of fine sediment. The translation of the eroded surface mentioned above suggests that the sediment delivery mechanism was a progressive slope failure, the collapsed material being washed into the stream. Stream observations in the vicinity of the Megaslump reveal that the embeddedness is above the average (Appendix B Photo 15). The larger cobble size particles are buried into finer sand-sized sediment in a proportion 25 to 40 percent suggesting a higher influx of sediment. Two other landslides, both smaller in size than the Megaslump, were documented in the east side of the valley. In the order of their relative size, these landslides are located 1) a short distance downstream of the Megaslump on the east side (Appendix B Photo 12) and 2) in the upstream ski hill area (approximately 2 miles upstream from the mouth) also on the east bank along a major meander bend (which based on aerial photographs migrated approximately 80 feet towards southeast between 1934 and 2003). In the vicinity of each of these landslides and a short distance downstream, the proportion of finer sediment trapped in the streambed (i.e., embeddedness) is higher than the typical average suggesting on-going erosion at all of these places. Other landslides, even smaller in size, are located in an upstream forested area where there has been little to no change in the land use. A series of three near-channel landslides have been documented within a short distance downstream of the Poplar Rapids, all on the west side of the valley (Appendix A Figure 1 and Appendix B Photos 27 and 28). This area is densely forested. Field observations and aerial photographs indicate no logging or other type of land alteration in recent years. This suggests that landslides could occur regardless of the changes in land use. To verify this assertion, a short trip to the Onion River, documented a landslide of considerable

20 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 17 of 24 dimensions (Appendix B Photo 34). The Onion River is a smaller stream flowing into Lake Superior with a watershed that is densely forested and experienced little to no land use alteration. Incision along Valley Slopes Gullies and Ravines Gullies and ravines are common erosion features in places of concentrated runoff along steep slopes. Such features are a common natural occurrence and part of the drainage basin denudation process. However, the gullies that are naturally occurring evolve relatively slowly into ephemeral tributaries to the main stream. By contrast, the erosion gullies that formed as the result of increased runoff from developed areas are fast evolving and can mobilize large amounts of sediment. There are several places of concentrated runoff from storm events within the Lower Poplar River valley that occur as a result of the recreational-based development (ski trails, ATV trails, access roads, ski lifts, resorts, facility buildings, etc). In some places, significant efforts have been made in recent years to limit, eliminate, or mitigate the gully erosion and to convey the runoff flow to the stream in a controlled, non-erosive way. Most notably, the runoff from the eastern tributary valley near Eagle Mountain where many of the ski trails and local roads are located is routed across a series of swales. These swales were landscaped across the slope with the apparent intent to break the slope surface into smaller segments and control the erosive power of the runoff (Appendix B Photo 23). Small size drains have been installed along the swales and efforts to vegetate and stabilize the sloped surfaces between swales have been made. A place of concentrated runoff that resulted into a large erosion ravine was identified in the very upstream part of the river. A 320-foot long ravine spans through a forested area from the north end of the main road (Ski Hill Road) to the edge of the stream (Appendix A Figure 1). This ravine is approximately 10 to 20 feet deep. The average longitudinal slope is approximately 21 degrees (40%). To a certain extent, the bottom of the ravine appears to be have been reinforced with debris and boulder rock material. The side slopes, however, are unvegetated and very steep (over 45 degrees) with potential for future soil erosion (Appendix B Photo 29). Given its size and proximity to the river, this erosion ravine is likely to contribute significant amount of fine sediment to the stream. The streambank at the bottom of this ravine shows a higher than average proportion of finer sediment (i.e., higher embeddedness, approximately 25 to 30 percent; Appendix B Photo 30). Another erosion ravine, smaller in size (approximately 180 feet long and 10 feet deep) is located in the main ski area on the east side of the valley. It extends from a ski lift post to the most upstream bridge before the rapids (Appendix A Figure 1; Appendix B Photo 22).

21 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 18 of 24 Localized Erosion within River Valley To some extent, all sloping surfaces along the Lower Poplar River valley are subjected to erosion processes that could result in fine sediment being delivered into the main stream. This applies even to some well-vegetated and forested areas that were not affected at all by human activities. However, those surfaces where land-use conversion from forest took place became more vulnerable to erosive processes and are likely to contribute a disproportionate amount of sediment to the stream. Based on field observation, several types of surfaces appear to be particularly vulnerable to erosion and may represent a major localized source of suspended sediment. These types of surfaces include ski trails, ATV trails, hiking trails, utilities road surfaces, road embankments, and roadside ditches (Appendix B Photos 16, 17, 32). Additionally, several landslides, at appreciable distances above and not directly related to the main stream, have been documented (Appendix B Photo 24). 5.2 Estimating the Amount of Stream Related Suspended Sediment within Lower Poplar River An approximate estimate of the annual average suspended sediment contributions from sources outlined in Section 5.1 is presented below. These geometric volume estimates are based on aerial photographs, historical (1934) and current (2003), and on topographic data (contours) coupled with field observation. For each area that appears to be eroded, or washed away by river migration, a minimum and maximum estimate of the length and width was determined through direct measurements from the map. The range of estimates account for and accommodate, the resolution and accuracy of the aerial photographs. The height is based on field observations of erosion surfaces. There are two major challenges to accurately estimate eroded volumes. First, it is difficult to estimate the exact timeframe over which the erosion took place. Second, but perhaps more important, the percentage of eroded material from each source that actually became suspended sediment is unknown. It is assumed that the sediment fraction related to the turbidity primarily consists of clay, silt, and fine sand. Based on field observation at the Megaslump and other landslides areas, the red clayey soils dominating the valley walls, have a considerable fraction of fine material that, once it reaches the stream, would become suspended sediment (i.e., mostly clay and silt). Based on visual observations, about one third of soil volume in the valley wall seems to fall in the clay and silt size range. A 25 to 40 percent range was used for the estimate presented in the table below. On the other hand, the streambed and stream banks contain very little fine sediment. The 5 to 10 percent range used in the table below is based on the assumption that the material in

22 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 19 of 24 the areas adjacent to the active flow, where the stream could potentially migrate, (i.e., the bottom of the valley that could be regarded as a narrow floodplain) consists primarily of a matrix of boulder and cobble. Thus, when the channel migrates laterally, less than half of the scoured material falls within clay to fine gravel range, of which a smaller fraction potentially resulted in suspended sediment. Based on these estimates, the following table is presented as a preliminary assessment of suspended sediment amount in the Lower Poplar River. Table 1. Estimates of Annual Average Suspended Sediment (Only from Stream Sources) Eroded Volume Estimates (CY) Typical Bulk Density (pcf) Proportion of Eroded Soil that becomes Suspended Sediment % Time Interval (years) Average Annual Suspended Sediment Flux (Tons/year) Min Max Min Max Min Max Channel Incision and Gradual Lateral Migration* 16,593 41, % 10% Megaslump 57,037 85, % 40% Other Landslides 22,500 33, % 40% * Meander cutoffs not included. The estimates, while approximate, suggest that channel itself represents only a minor source of suspended sediment while the landslides could generate an amount of suspended sediment that is an order of magnitude higher. Rough estimates of suspended sediments from the major erosion ravines indicate a total quantity between 1500 and 2800 tons. However, the age of these erosions ravines is largely unknown. It could vary between several years to forty years (i.e., since the beginning expansion of skiing areas) resulting in annual suspended sediment rates that could range from 40 to 500 tons. It would be fair to conclude that the largest erosion ravine documented upstream of the ski hill is relatively young and represent a significant source of sediment.

23 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 20 of 24 6 Conclusions The physical channel assessment was conducted during a single visit to the watershed lasting 4 days. Estimates of sediment loading to the Poplar River were based on field observations and photographs taken during the site visit and compared with historical photographs and maps. This limited field investigation limits the certainty of the estimates to the range of values reported. Stream Type The Lower Poplar River is a steep and high-energy, mountain stream. The active channel lacks a floodplain and is largely confined within a relatively steep and narrow valley. The bottom width of the valley varies, allowing for some local channel mobility in the form of gradual lateral migration coupled with channel bed incision. There is also evidence of sudden migration in form of meander cut-offs. The channel bed and banks are dominated by coarse, cobble and boulder size, material. The fine sediment transport capacity exceeds the supply from the valley walls. A limited amount of finer bed material, predominantly coarse sand to fine gravel is trapped between the larger particles. Stream Sediment The channel bed and banks are dominated by coarse, cobble and boulder size, material. The fine sediment transport capacity exceeds the supply from the valley walls. A limited amount of finer bed material, predominantly coarse sand to fine gravel is trapped between the larger particles. Given the strongly bi-modal sediment distribution, a D50 analysis was not carried out. Primary Sources of Turbidity in Lower Poplar River Six sources of turbidity in the stream are identified and discussed in Section 5.1. These are: Channel bed incision Sudden channel migration Stream-bank erosion Landslides near active channel Incision along valley slopes Localized erosion within river valley Of these sources, our preliminary assessment indicates primary long term sources of turbidity in the system are landslides, sudden channel migration, and incision along valley slopes.

24 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 21 of 24 Evidence of Landslides as Natural Processes Given the interest in understanding the anthropogenic effect on the system, it is important to outline that within the Lower Poplar System, there is good evidence that landslides occur as a natural process, irrespective of land alteration. However, in the case of the Megaslump, land alteration and concentrated runoff in recent years may have increased the amount of erosion and sediment that was dislodged from the valley wall and delivered into the stream. Collectively, the landslides are a significant source of sediment including an important fraction of suspended sediment. A multitude of other places susceptible to erosion within the river valley can be attributed to land-use changes, development of the multi-use trail system, and general grading operations. Collectively, these places represent a significant source of suspended sediment and include ski trails, ATV trails, utility/access roads and their embankments, roadside ditches and some of the landslides located further away from the stream. Quantity of Suspended Sediment Our preliminary assessment presented in Table 1 indicates that the largest source of suspended sediment in Lower Poplar near-stream system is from the Megaslump and the other landslides. The Megaslump feature appears to have contributed nearly 60-70% of the suspended sediment in the system. Channel incision and lateral migrations appear to provide the rest of the suspended sediment in the system. Finally, as indicated in the Executive Summary of this document, it is important to underscore that the geomorphology assessment is only one piece of a puzzle of many pieces. A more accurate estimate of suspended sediment loading is expected to be an outcome of the modeling component of this TMDL project, and observations presented here-in are meant to establish markers for that study.

25 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 22 of 24 7 References Cui Y., Parker, G., Pizzuto, J, and Lisle, T.E., Sediment pulses in mountain rivers; 3. Comparison between experiments and numerical predictions. Water Resources Research, v. 39 No. 9, p. 4-1:4-11. Fitzpatrick, F.A., Peppler, M.C., DePhilip, M.M., and Lee, K.E Geomorphic Characteristics and Classification of Duluth-Area Stream, Minnesota. USGS Scientific Investigation Report 54 pp. Montgomery, D.R. and Buffington, J.M., Channel-reach morphology in mountain drainage basins. GSA Bulletin, v.109, p Montgomery, D.R. and MacDonald L.H., Diagnostic Approach to Stream Channel Assessment and Monitoring. Journal of American Water Resources Association, v. 38, p RTI, Poplar River Turbidity Total Maximum Daily Load Evaluation of Existing Data. Prepared for US EPA Region 5, 77 West Jackson, Chicago, IL Prepared under contract 68- C August 16, Wohl, E.E., Mountain Rivers. American Geophysical Union, 320 pp.

26 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 23 of 24 8 Appendices

27 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 24 of 24 Appendix A Maps of Study Area, Field Notes, Longitudinal Profile and Cross Sections

28 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) 1. Cross Section I - Near River Mouth Channel 50 to 80 feet wide. Maximum depth about 2 feet. Bed dominated by boulder and cobble material, 4 to 15 inches in size. Embeddedness 10 to 20%, coarse sand and fine gravel. Banks - stable, limited slope erosion. Vegetation - trees of various sizes. Other observations boulder mid-channel bar, deep pool (over 6 ft) downstream of the falls. 2. Highway 61 (downstream) Falls A sequence of Falls extend north and south of Highway 61 Total drop of approximately 100 feet over about 900 feet distance. At Hwy 61 channel is less than 30 feet wide. Potholes developed in bedrock (basalt). Banks well vegetated mature trees. 3. Cross Section II Golf Course Bridge at downstream sampling station. Channel width 40 to 60 feet. Channel depth ~ 2 feet. Bed material mostly boulder and cobble. With little fines (i.e., small embeddedness). Vegetation: Small trees and brushed on east bank, grasses on west bank. Golf course maintained surface. Other observations: Mid-channel bar downstream of bridge. Abandoned channel bed on the east side. 4. Cross Section III Bridge on Golf Course, about 1 mile upstream from the mouth and ¼ miles downstream from the Megaslump. Channel width 25 to 35 feet. Channel depth a little over 1 foot. Bed covered by boulders and cobble with very little fines (low embeddedness). Banks stable, no signs of erosion. Vegetation dense trees and brushes and maintained grass surface (golf course) Other observations - Steep gradient and high flow velocity, bedrock downstream of bridge. 5. Another Bridge on Golf Course about 500 feet upstream. Channel width 40 to 50 feet. Channel depth 1 to 2 feet. Bed boulder and cobble. West bank bedrock. East bank cobble and boulder. Some sand trapped near eastern bank. Bank are well vegetated, no signs of erosion. Some large wood debris. 6. Landslide (slump) downstream of Megaslump. A landslide approximately 50 feet wide and 30 feet high. Steep slope (about 30 degrees) with almost no vegetation. 7. Megaslump Approx. 45 to 50 feet high. Plane of failure (nearly 45 degrees) and appears to experience on going erosion (i.e. rills, soft friable soils). Large boulders and cobbles are encased in a finer matrix of reddish sand, silt, and clay. Coarse material formed a talus and a bench at the toe of the slope adjacent to the active channel. A couple of large erosion ravine and several smaller ones dissect the face of the slope of failure. Channel bed boulder and cobble dominated. Percentage of fines (embeddedness) is considerably higher, particularly in the megaslump bank. Other observations previous channel bed armored with cobbles present in opposite bank approximately 2 feet above present bed elevation. 8. Cross Section IV Appox. 200 feet upstream of the Megaslump. Channel width 40 to 50 feet. Channel depth 1.5 feet. Channel bed boulder and cobbles. Stable banks. Vegetation a mix of young and mature trees. 9. Upstream of Megaslump long reach of stable, densely vegetated channel. Densely vegetated banks, mature trees, very little large wood debris. Other observations water pool for snow making operations west of river.

29 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) 10. Cross Section V - Ski hill area Downstream Bridge. Flow splits into two channels with a separating island bar. Channel width about 50 feet. Depth varies from point to point because the channel bed is boulder dominated. Banks show little signs of erosion (trees dislodged). Higher percentage of fines (increased embeddedness) observed near the banks. Other observations abandoned channel with large boulders bed east of main channel. 11. Cross Section VI Ski hill area Middle Bridge. Channel width about 50 feet. Depth varies from point to point because the channel bed is boulder dominated. Banks are armored with boulder size material. Very little fine material. Other observations small slumps present in the east side above the channel area. A larger slump is present further upstream. 12. Ski hill area Upstream Bridge. Large boulders dominate bed. Step-pool morphology. Downstream of the bridge there is a higher percentage of fines near eastern bank possibly due to an erosion ravine. 13. Erosion Ravine downstream of Poplar Rapids. 15 feet deep and 40 feet wide ravine on the east bank. Steep (nearly 45-degrees) side slopes. Ravine originates from a storm water pool near Ski Hill Road. Material observed on each side is a poorly sorted mix of sand silt and clay. A high percentage of fines (high embeddedness) observed on the east (ravine) side of the stream. 14. Area downstream of Poplar River Rapids Bed dominated by large boulders and blocks of basalt. High energy flow. A series of three slumps are present on the west side, about 50 to 100 feet from the stream. Lower Poplar River - Longitudinal Profile Upstream Rapids 1100 Elevation (ft) Lake Superior (599) Downstream (Hwy 61) Falls Distance Upstream (ft)

30 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) Cross Section I 4 3 Depth / Bank Height (ft) Distance (ft) Cross Section II 4 3 Depth / Bank Height (ft) Distance (ft) Cross Section III Depth / Bank Height (ft) Distance (ft)

31 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) Cross Section IV 6 5 Depth / Bank Height (ft) Distance (ft) Cross Section V 6 5 Depth / Bank Height (ft) Distance (ft) Cross Section VI 4 3 Depth / Bank Height (ft) Distance (ft)

32 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) CROSS-SECTIONS DATA: XS I Pt # Distance Depth/Height XS II Pt # Distance Depth/Height XS III Pt # Distance Depth/Height XS IV Pt # Distance Depth/Height XS V Pt # Distance Depth/Height XS VI Pt # Distance Depth/Height

33 LOWER POPLAR RIVER GEOMORPHOLOGIC ASSESSEMENT, JULY 2 5, FIELD NOTES, LONGITUDINAL PROFILE, AND CHANNEL CROSS-SECTIONS (6) Longitudinal Profile Approximated Distance (feet from mouth) USGS Elevation (feet)

34 Physical Channel Assessment of the Lower Poplar River 25 February 2008 Page 25 of 24 Appendix B Field Photographs

35 Photo 1 Near River Mouth Photo 2 River Mouth Lower Poplar River Physical Channel Assessment Field Photos Appendix B

36 Photo 3 Cross section I Photo 4 Cross section I Typical Streambed Lower Poplar River Physical Channel Assessment Field Photos Appendix B

37 Photo 5 Cross Section II Golf Course area upstream of Monitoring Station Bridge Photo 6 Streambed at Cross Section II Lower Poplar River Physical Channel Assessment Field Photos Appendix B

38 Photo 7 Cross Section III Golf Course Area, next bridge upstream from Monitoring Station Photo 8 Cross Section III Looking Upstream Lower Poplar River Physical Channel Assessment Field Photos Appendix B

39 Photo 9 Plane Bed Typical Reach Photo 10 Step and Pool Typical Reach Lower Poplar River Physical Channel Assessment Field Photos Appendix B

40 Photo 11 Golf Course Upstream Bridge Bedrock section Photo 12 Smaller slump downstream of Megaslump Lower Poplar River Physical Channel Assessment Field Photos Appendix B

41 Photo 13 Megaslump Viewed from East Bank Photo 14 Megaslump Wide view Lower Poplar River Physical Channel Assessment Field Photos Appendix B

42 Photo 15 Fine sediment at Megaslump location Photo 16 Access road leading to Megaslump Lower Poplar River Physical Channel Assessment Field Photos Appendix B

43 Photo 17 ATV trail downhill from Eagle Mountain Resort Photo 18 Strom water pond downhill from Eagle Mountain Resort Lower Poplar River Physical Channel Assessment Field Photos Appendix B

44 Photo 19 Cross Section V Photo 20 Cross Section V Streambed Lower Poplar River Physical Channel Assessment Field Photos Appendix B

45 Photo 21 Slump river bend downstream of Ski Hill (East side) Photo 22 Erosion Ravine near Ski Hill Lower Poplar River Physical Channel Assessment Field Photos Appendix B

46 Photo 23 Ski hill revegetated with erosion control landscaping Photo 24 Example of landslide located well above and away from stream (Ski Hill) Lower Poplar River Physical Channel Assessment Field Photos Appendix B

47 Photo 25 Cross section VI Photo 26 Cross section VI streambed Lower Poplar River Physical Channel Assessment Field Photos Appendix B

48 Photo 27 Upstream landslide about feet downstream from Poplar Rapids Photo 28 Another upstream landslide about feet downstream from Poplar Rapids Lower Poplar River Physical Channel Assessment Field Photos Appendix B

49 Photo 29 Major Erosion Ravine East side of valley upstream of Ski Hill Photo 30 Stream bank near major Erosion Ravine on east side of valley upstream of Ski Hill Lower Poplar River Physical Channel Assessment Field Photos Appendix B

50 Photo 31 Ski Hill Road Photo 32 Access road and roadside ditch - example Lower Poplar River Physical Channel Assessment Field Photos Appendix B

51 Photo 33 Poplar River Upper Watershed (upstream of Poplar Rapids and study area) Photo 34 Onion River landslide (height is approximately 30 feet) Lower Poplar River Physical Channel Assessment Field Photos Appendix B