HomeMy WebLinkAbout10 oct 2014 packet joint with ostAgenda items are subject to change – Times are approximate and are also subject to change
Town of Snowmass Village Town Hall - (map attached)
130 Kearns Road – Snowmass Village, CO
Time Description
12:00 PM • Joint Meeting with Open Space and Trails Board
North Star Geomorphological Assessment Presentation –
Golder Associates Inc.
2:00 PM • Adjourn
GEOMORPHIC ASSESSMENT
North Star Nature Preserve
Submitted To: Mr. Gary Tennenbaum Assistant Director
Pitkin County Open Space and Trails 530 East Main Street, Third Floor Aspen, Colorado 81611
Submitted By: Golder Associates Inc. 44 Union Boulevard, Suite 300
Lakewood, Colorado 80228
October 17, 2014 1400717 004 R Rev1
RE
P
O
R
T
Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation
October 2014 ES-1 1400717 004 R Rev1
EXECUTIVE SUMMARY
The geomorphology of the North Star Nature Preserve consists of a relatively low gradient meandering
alluvial channel whose lateral boundaries are defined by the glacially carved valley in which the site
resides. The presence of the meandering channel for the Roaring Fork River is controlled by the presence
of a terminal moraine that spans the valley width. This moraine acts as a dam that temporarily blocks the
passage of water and sediment for a short length of the valley. In the past, this accumulated sediment has
held an active meandering channel that migrated laterally across the valley floor. The valley is located in
the tectonically uplifting Rocky Mountains upstream of Aspen, Colorado. The Roaring Fork River, like
most rivers in this landscape, is actively incising into the bedrock that contains it. This process of incision
is occurring on the time scale of geologic events and it is temporarily halted near the site by the
aggradation of sediment behind the moraine dam. In relatively recent pre-historic time, the general
incision of the river into the landscape has started to breach the moraine and caused the meandering
channel to straighten substantially. Thus, the meanders preserved in the valley floor sediments are relicts
from a former state of morphologic equilibrium. In more recent historic past, anthropogenic activities have
halted this incision and resulted in a new state of equilibrium in which the river is still a meandering,
although straighter, channel that is disconnected from its floodplain. Two fundamental land use activities
have altered the hydrology of the site: first and most significantly, is the construction of the Transmountain
Diversion, which extracts a large portion of the total annual discharge of the Roaring Fork River; and
secondly is the agricultural activities that took place on the site. The construction of the Diversion
decreased the capacity of the river to move sediment and consequently halted the incision into the
moraine dam. The agricultural practices applied on the site fall into two categories- river straightening and
water table lowering. The river straightening was likely to counteract the sedimentation produced by the
Diversion, and the water table lowering was intended to improve the land for crops. While the river
straightening has had an observable, but minimal, impact relative to the Diversion, the ditching and
channelization has had significant effects on the local ecology. The adjacent floodplain and hillslope that
was previously largely wetland and controlled by the adjacent hillslope hydrology, is transitioning into a
drier ecological environment through the diversion of water via existing surficial channels controlled by
operational headgates.
Golder proposes to limit the potential for further lowering of the water table by modifying the local
hydraulic controls to maintain a stable hydraulic gradient. Additionally there are specific portions of the
site where bioengineering solutions are recommended to prevent the erosion of a stream bank supporting
high value habitat.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 i 1400717 004 R Rev1
Table of Contents
EXECUTIVE SUMMARY ........................................................................................................................ ES-1
1.0 INTRODUCTION .............................................................................................................................. 1
2.0 APPROACH ..................................................................................................................................... 3
3.0 ASSESSMENT OF PHYSICAL PROCESSES THROUGH TIME ................................................... 4
3.1 Glaciation ..................................................................................................................................... 4
3.2 Hydrology ..................................................................................................................................... 6
3.2.1 Intra-Annual Hydrology............................................................................................................. 6
3.2.2 Inter-Annual Hydrology and Bankfull Discharge ...................................................................... 7
3.2.3 Bankfull Discharge Method Selection ...................................................................................... 7
3.2.4 Maximum Annual Discharge .................................................................................................... 8
3.2.5 Recurrence Interval Calculations ............................................................................................. 9
3.2.6 Selection of a Bankfull Discharge Recurrence Interval .......................................................... 10
3.2.7 Bankfull Discharge ................................................................................................................. 10
3.2.8 Trans-Mountain Diversions .................................................................................................... 10
3.3 Channel Plan Form .................................................................................................................... 11
3.3.1 Alignment ............................................................................................................................... 11
3.3.2 Sinuosity ................................................................................................................................. 15
3.3.3 Top Width ............................................................................................................................... 15
3.3.4 Meander Belt Width ................................................................................................................ 16
4.0 EROSION CALCULATIONS .......................................................................................................... 19
4.1 Stream Power Calculations ........................................................................................................ 19
4.2 Soil Erodibility Calculations ........................................................................................................ 23
4.3 Erosion Assessment .................................................................................................................. 24
4.4 Field Investigation ...................................................................................................................... 24
5.0 DISCUSSION ................................................................................................................................. 25
5.1 Ecological significance ............................................................................................................... 25
5.2 Role of the Trans-Mountain Diversions ...................................................................................... 25
5.3 Morphologic Stability .................................................................................................................. 25
5.4 Bank Erosion .............................................................................................................................. 26
5.5 Headgates and Wetland Hydrology ........................................................................................... 26
5.6 In-Stream Structures .................................................................................................................. 27
5.7 The Smith Property .................................................................................................................... 27
5.8 Long-Term Channel Incision ...................................................................................................... 27
6.0 CONCLUSIONS ............................................................................................................................. 29
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 ii 1400717 004 R Rev1
7.0 RECOMMENDATIONS .................................................................................................................. 30
8.0 REFERENCES ............................................................................................................................... 32
List of Tables
Table 1 Recurrence Interval of Flows near Bankfull Conditions .................................................... 10
Table 2 Sinuosity of the Roaring Fork River at North Star ............................................................. 15
Table 3 Channel Top Width of the Roaring Fork River at North Star ............................................ 16 Table 4 Belt Width of the Roaring Fork River at North Star ........................................................... 18
Table 5 Root Ball Size .................................................................................................................... 23
List of Figures
Figure 1 Site Location Map ............................................................................................................... 2
Figure 2 Geologic Map (Aspen Quadrangle, Colorado, Map I-785-H (Bryant 1971)) ....................... 4 Figure 3 1990 Infrared Aerial Photograph of the Historic Meander Pattern within the North
Star Nature Preserve Area (Clark et al. 2008) .................................................................... 5 Figure 4 Daily Discharge Statistics for the Period of Record at Roaring Fork Gauge
#09073400 (USGS 2014) ................................................................................................... 6 Figure 5 Average Total Monthly Precipitation, Snow Fall, and Snow Depth for
Independence Pass (Station 054270) for Period 7/1/1947–1/31/1980 (Kolm and ven der Heijde 2011) ........................................................................................................... 7
Figure 6 Maximum Annual Discharge for Gauge #09073400 (USGS 2014) .................................... 8 Figure 7 Recurrence Interval Analysis for Gauge #09073400 (USGS 2014) ................................. 10
Figure 8 Roaring Fork River Alignment in 1893 .............................................................................. 12 Figure 9 Roaring Fork River Alignment in 1951 .............................................................................. 12
Figure 10 Roaring Fork River Alignment in 1958 .............................................................................. 13 Figure 11 Roaring Fork River Alignment in 1983 .............................................................................. 13
Figure 12 Roaring Fork River Alignment in 1999 .............................................................................. 14 Figure 13 Roaring Fork River Alignment in 2011 .............................................................................. 14
Figure 14 Sinuosity at North Star Preserve and the Smith Property through time. .......................... 15 Figure 15 Meander Variables ............................................................................................................ 17
Figure 16 North Star Preserve and Smith Property Meander Belt Width Sinuosity through Time .................................................................................................................................. 17
Figure 17 Definition Schematic of Channel Geometry and Hydraulic Variables (Odgaard 1986) ................................................................................................................................. 20
Figure 18 Transverse Bed Slope, sTc, as a Function of Distance, s, for Cross Section 2 ............... 21 Figure 19 Headgate structure in North Star Preserve ....................................................................... 27
List of Appendices
Appendix A Photo Log
Appendix B Soil Samples
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 1 1400717 004 R Rev1
1.0 INTRODUCTION
This report prepared by Golder Associates Inc. (Golder) presents the results of the geomorphic
assessment of the Roaring Fork River through the North Star Nature Preserve (North Star). This
geomorphic assessment was undertaken as part of the ecological services for Pitkin County Open Space
and Trails (OST) being provided by Golder and Colorado Wildlife Science, LLC. The assessment was
conducted by Golder with fieldwork occurring July 28 – 30, 2014. Subsequent survey data was collected
by SGM Inc. in August 2014. During the field survey, SGM collected detailed cross section surveys at the
seven locations identified in Figure 1. These seven locations serve as the assessment points for this
investigation.
The Roaring Fork River flows adjacent to Highway 82 from Independence Pass at about 12,000 feet (ft) to
the confluence of the Colorado River in Glenwood Springs at about 5700 ft. The total length of the river is
about 70 miles. The study area extends from the Smith Open Space to near Highway 82 and Stillwater
Road (Red outline in Figure 1). The Roaring Fork River travels approximately 4900 ft through the study
area. The drainage area upstream of the downstream boundary of the study is approximately 106 square
miles (mi²). The elevation of the valley floor within the project area is approximately 8030 ft above sea
level.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 2 1400717 004 R Rev1
Figure 1 Site Location Map
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 3 1400717 004 R Rev1
2.0 APPROACH
Golder investigated the geomorphic characteristics of the Roaring Fork using a process-based method
(Leopold et al 1964). The initial steps in the investigation were to assess the current and historic site
conditions, to observe the processes of the river, and to assess the potential for modern and future
geomorphic change. After assessing the processes that drive long-term stability and short-term river
dynamics, Golder will make recommendations for potential remedial actions. Remedial action is not a
foregone conclusion, as the best course of action may be non-intervention. The primary goal of this
investigation is characterization of the river processes to develop an understanding of the current
conditions within the context of past and potential future events. Remedial design measures will only be
recommended if their application is deemed appropriate to achieve project goals.
The goal for the North Star project is to work within an adaptive management process and to facilitate the
creation of a balance between the river’s current quasi-equilibrium morphology and the critical
infrastructure within the site. This balance implies allowing the river to migrate freely, while maintaining its
morphologic characteristic and ecological function, while at the same time maintaining critical
infrastructure and safe recreational opportunities. These goals will be accomplished through OST’s
adaptive management program, as will be supported through this document. This collaborative
philosophy has guided the process, conclusions, and recommendations for this investigation into the
North Star Nature Preserve.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 4 1400717 004 R Rev1
3.0 ASSESSMENT OF PHYSICAL PROCESSES THROUGH TIME
Historic observations are a critical component of a geomorphic assessment. Evidence of change in the
patterns of the spatial and temporal distribution of the water, sediment, and geomorphic features of the
site were used to assess its morphologic character. Sudden or gradual changes in these variables can
potentially indicate that the processes that define the site are undergoing changes.
3.1 Glaciation
Glacial activity during the late Pleistocene Epoch (ending about 11,000 years ago) formed a wide, low-
gradient valley (Bryant 1979). The sediment deposited by the glacier, both during and after recession,
often forms the modern landscape features that control the location and hydrology of stream and riparian
areas. During recession of the glacier that formerly occupied the Roaring Fork valley, there was a
temporary pause in its retreat up the valley. This pause resulted in the deposition of a terminal moraine,
or recessional moraine, at the toe of the glacier (Figure 2). After the eventual retreat of the glacier up the
valley, this moraine began to act as a natural dam, behind which a thick deposit of alluvium formed. This
accumulated alluvial material can be as much as 300 feet thick (Hickey et al. 2000). In the modern
setting, this moraine dam controls the site hydraulics and maintains the low-gradient sinuous stream and
low-lying wetland morphology of the site.
Figure 2 Geologic Map (Aspen Quadrangle, Colorado, Map I-785-H (Bryant 1971))
Moraine
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 5 1400717 004 R Rev1
The surficial characteristics of the site are well represented in the infrared aerial photograph shown in
Figure 3. The open water shows as a black color, and Highway 83 is the linear blue line on the right of the
photograph. Some of the most striking features of this photograph are the in-filled oxbow lakes, which are
displayed as red semi-circular features on the left bank of the river. These arcs identify the former
locations of the river that have been filled with sediment after the river moved to a new alignment. These
features indicate that at some point in the past, the river migrated over a large portion of the valley floor.
Although in the absence of context provided by other data sources this evidence could be interpreted as a
high rate of modern geomorphic change, the data presented herein shows that the rate of geomorphic
change has decreased over time and that the filled oxbow lakes are indicative of a greater rate of
dynamic change that occurred in the past and is no longer defining the modern valley morphology.
Figure 3 1990 Infrared Aerial Photograph of the Historic Meander Pattern within the North Star Nature Preserve Area (Clark et al. 2008)
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 6 1400717 004 R Rev1
3.2 Hydrology
3.2.1 Intra-Annual Hydrology
The USGS gaging station #09073400 on the Roaring Fork River near Aspen, Colorado, is the closest
stream gauge to the North Star Nature Preserve and is located in proximity to the moraine. The period of
the discharge record spans from 1964 to the present. It is important to note that the period of record for
the hydrologic data occurs after the Transmountain Diversion, whose influence is discussed in Section
3.2.8.
The drainage area for the gauge is 106 mi2 and the elevation is 8014 ft. The Roaring Fork River has a
nivally dominated discharge pattern, in which the maximum discharge events are associated with the
snowmelt of the summer months. Figure 4 depicts the mean, minimum, and maximum values for each
day of the year. The maximum discharge event of each year is most likely to occur between May and
July. This pattern is similar to that observed (Wohl 2008) on Front Range drainage basins above 2300
meters (7545 ft), in which discharge patterns are dominated by snowmelt hydrology. Wohl (2008) notes
that Pleistocene alpine glaciation strongly influences the valley geometry above elevations of 2300 m
(7550 ft). The North Star Nature Preserve is located above this threshold elevation. The general
observation of glacial influence is confirmed by the fundamental role that the moraine present at the
downstream end of the study area plays in the site hydrology. Not coincidentally, the period during which
the most water is abstracted from the watershed by the Transmountain Diversion is the same as the time
of year in which the maximum discharge occurs.
Figure 4 Daily Discharge Statistics for the Period of Record at Roaring Fork Gauge #09073400
(USGS 2014)
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 7 1400717 004 R Rev1
The conclusions drawn concerning the dominance of snowmelt, over precipitation, on the site hydrology
are confirmed by the precipitation data displayed in Figure 5. The majority of the precipitation events
occur outside of the months of highest discharge. Precipitation that falls on the site typically occurs as
snow in the winter months.
Figure 5 Average Total Monthly Precipitation, Snow Fall, and Snow Depth for Independence Pass (Station 054270) for Period 7/1/1947–1/31/1980 (Kolm and ven der Heijde 2011)
3.2.2 Inter-Annual Hydrology and Bankfull Discharge
The assessment of a characteristic, or channel forming, discharge is a meaningful method of interpreting
the channel geometry’s relation to the flux of water and sediment through the fluvial system. The
characteristic discharge is the discharge event that is large enough to move a significant quantity of
sediment, and occurs frequently enough as to define the channel geometry. This discharge event is
termed the effective discharge and is equated with the bankfull discharge. Bankfull discharge can also be
defined as the maximum discharge that the channel can convey without overflowing on to the floodplain.
While effective discharge and bankfull flow are not exactly the same, their values are equated for practical
restoration purposes (Klasz et al. 2012). As the effective discharge calculated in this report is derived
from a post Transmountain Diversion hydrologic data set, a comparison of this discharge to the ability of
the river to interact with its bank material will be used to assess the connection of the modern hydraulics
to the existing landscape.
3.2.3 Bankfull Discharge Method Selection
Bankfull flow can be estimated via two methods. One method identifies specific characteristics of the
channel geometry and relates the characteristics to the discharge associated with their formation, and the
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 8 1400717 004 R Rev1
second assesses the recurrence interval of the largest storm within each year for the period of record and
selects the discharge value associated with a specific recurrence interval. In the following section, we
discuss the selected method and assess the trends observed within the results.
Ideally, both the bankfull indicator and the recurrence interval methods would be used to assess the
bankfull discharge. However, when the bankfull indicators were used to assess the discharge at several
surveyed locations during this investigation, the results were inconsistent, likely due to the influence of the
Transmountain Diversions on the hydrology. There is the potential that the use of a two-dimensional
hydraulic model, which incorporated the role of the sinuous channel, could enable the use of these
bankfull characteristics as a method of estimating discharge of the pre diversion hydraulics. Golder
believes that these inconsistent results invalidate the use of this method in this study, and therefore these
results are not presented. Consequently, Golder has relied on the recurrence interval method to define
the bankfull discharge. It is important to note that the data set used to calculate the recurrence interval is
solely derived from the hydrologic record collected after the construction of the Transmountain
Diversions.
3.2.4 Maximum Annual Discharge
The assessment of the recurrence interval of the discharges within a period of record is conducted as
follows. Initially, the maximum discharge for each year is identified (Figure 6).
Figure 6 Maximum Annual Discharge for Gauge #09073400 (USGS 2014)
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 9 1400717 004 R Rev1
The temporal occurrence of the high and low discharge years does not display a significant trend within
the period of record (Figure 6). This indicates that there has not been a fundamental change in the
hydrologic regime since 1965.
3.2.5 Recurrence Interval Calculations
With the maximum annual discharges identified, the calculation of the recurrence interval proceeds as
follows. The maximum annual discharges are ranked in increasing order by discharge, with the largest
maximum discharge being given a rank of 1, and the minimum value equaling the number of years in the
continuous record. In this case, there are 49 years of continuous record.
Golder used two equations to calculate the recurrence interval of the discharge events, one based on the
earlier work by Gumbel (1958) and subsequent work by Gringorten (1963). These equations are applied
to each value of in the maximum discharge time series. The Gumbel equation takes the form:
𝑇𝑇=𝑛𝑛+1𝑚𝑚
And the Gringorten adaptation of the equation takes the form:
𝑇𝑇=𝑛𝑛+0.12𝑚𝑚−0.44
In both of these equations, T is the recurrence interval in years, n is the total number of years in the
record, and m is the rank of the discharge event. The Gumbel and the Gringorten methods both result in
very similar assessments of the data.
Prior to identifying a bankfull discharge from these assessments, a minimum of data cleaning must take
place. This cleaning is necessary to exclude the statistical outliers that have the potential to skew the
results of a recurrence interval assessment. The reason that these points are outliers is likely that they
belong to much larger populations that are not represented by the relatively short time series collected
during the period of record. In this investigation, the identification of the points to be excluded is done
based on professional judgment. Figure 7 depicts the recurrence interval of each discharge event relative
to the discharge of that event. Logarithmic trend lines are fit to the cleaned data for both the Gumbel and
Gringorten methods. Note that the formulas that represent these lines are very similar. Due to this
similarity, only the results from the Gumbel trend line are presented in subsequent sections. The
remaining task is to identify the recurrence interval associated with the bankfull discharge and then
identify the discharge of that recurrence interval.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 10 1400717 004 R Rev1
Figure 7 Recurrence Interval Analysis for Gauge #09073400 (USGS 2014)
3.2.6 Selection of a Bankfull Discharge Recurrence Interval
The selection of a recurrence interval that defines the bankfull discharge is a debated topic in the
geomorphic literature. General consensus has defined this value as ranging from 1 to 2.5 years (Klasz et
al. 2012), although substantial outliers have been observed. For the purpose of this investigation, Golder
has selected the recurrence interval value of 2 years based on professional judgment.
3.2.7 Bankfull Discharge
The discharge was calculated for multiple recurrence intervals from 1.5 to 2.1 (Table 1) using the trend
line fit to the Gumbel recurrence interval results. For erosion calculations presented later in the text, the 2-
year discharge of 721 cfs was used to represent bankfull conditions.
Table 1 Recurrence Interval of Flows near Bankfull Conditions
Time
(years)
Q: Gumbel
(cfs)
1.5 564
1.8 663
2 721
2.1 747
3.2.8 Trans-Mountain Diversions
The Transmountain Diversion, finished in 1937, has diverted a significant portion of the water from the
Upper Roaring Fork watershed each year since construction. The water is diverted to the eastern side of
the Continental Divide to supply water to the communities of the Front Range (Clark et al. 2008). This
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 11 1400717 004 R Rev1
diverted water decreases the peak discharge rate of the high magnitude events and shifts the timing of
the occurrence of the peak to later in the year. This decrease in peak discharge likely has significant
geomorphic and ecological implications that are discussed in Section 5.2 below.
3.3 Channel Plan Form
Four variables were evaluated for the channel plan form assessment:
Alignment
Sinuosity
Top Width
Meander Belt Width
3.3.1 Alignment
To evaluate the channel alignment, Golder used historic aerial photography and maps provided in Miller
and Ayers (2011). Figure 8 through Figure 13 present these images and maps that have been made
transparent and overlaid on a modern image from Google Earth. The congruence of the channel
alignments in the historic and modern landscapes (Figure 8 through Figure 13) illustrate that the channel
alignment has not changed significantly since 1893. This indicates that the abandoned oxbows present
on site were formed over 100 years ago and that the agricultural practices from the 1950s to the 1980s
are likely to have not played a substantial role in straightening the channel. The channel is not actively
migrating across the floodplain during the period of this photographic record, which spans from 1893 to
the 2011.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 12 1400717 004 R Rev1
Figure 8 Roaring Fork River Alignment in 1893
Figure 9 Roaring Fork River Alignment in 1951
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 13 1400717 004 R Rev1
Figure 10 Roaring Fork River Alignment in 1958
Figure 11 Roaring Fork River Alignment in 1983
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 14 1400717 004 R Rev1
Figure 12 Roaring Fork River Alignment in 1999
Figure 13 Roaring Fork River Alignment in 2011
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 15 1400717 004 R Rev1
3.3.2 Sinuosity
Sinuosity is calculated as the ratio of channel length by valley length, or the ratio of valley slope to
channel slope. In this case, the sinuosity was calculated as the ratio of the channel length to the valley
length using the images in Figure 8 through Figure 13. The channel sinuosity has remained relatively
consistent over the past 120 years, with a low rate of increase and some subtle variations that Golder
believes can be correlated to specific events (Table 2 and Figure 14). A discussion of the trends observed
in this graph is presented below.
Table 2 Sinuosity of the Roaring Fork River at North Star
Year
Sinuosity
Smith
Property
North Star
Open Preserve
1893 1.68 1.10
1951 2.03 1.29
1958 1.91 1.24
1983 1.95 1.29
1999 1.99 1.28
2011 1.99 1.28
2014 2.04 1.35
Figure 14 Sinuosity at North Star Preserve and the Smith Property through time.
3.3.3 Top Width
Channel top width is defined as the width of the water surface at bankfull flows. Due to the resolution of
the historical imagery, it is difficult to quantify changes in the channel top width through time. It was
determined that the Google Earth imagery would present the best option for assessing channel top width,
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 16 1400717 004 R Rev1
because images exists for the past 25 years. However, because the resolution of the aerial photographs
will introduce some error in the measurements, the values presented in Table 3 should be viewed as
relative and not absolute. Table 3 shows that the top width of the channel has not significantly changed
during the past 25 years.
Table 3 Channel Top Width of the Roaring Fork River at North Star
Date
Channel Width (ft)
Cross Section 1
Cross Section 2
Cross Section 3
Cross Section 4
Cross Section 5
Cross Section 6
Cross
Section 7
9/6/1999 67 75 63 70 57 96 51
11/19/2003 57 93 58 71 62 88 44
9/28/2004 68 93 53 72 57 88 54
10/22/2005 68 92 74 72 59 92 54
3/26/2006 68 89 74 72 60 92 54
7/6/2009 70 104 74 72 61 84 60
6/3/2011 64 104 62 79 60 86 59
9/22/2011 63 77 62 75 60 83 55
10/27/2011 64 - - - - 65 -
10/7/2012 60 85 66 74 60 85 51
8/1/2014 57 88 61 79 60 96 64
9/6/1999 67 75 63 70 57 96 51
Note: 10/27/2011 survey partially covered in shadow.
3.3.4 Meander Belt Width
Meander belt width is also defined as meander amplitude. The variable is illustrated in Figure 15. The
meander belt width is anticipated to remain constant through time, because the sinuosity of the stream
has remained constant through time. Figure 16 and Table 4 illustrates that this assumption is correct. The
only location where the meander belt width has changed is on the Smith property. However, this reach of
the river has been about the same since the late 1950s.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 17 1400717 004 R Rev1
Figure 15 Meander Variables
Figure 16 North Star Preserve and Smith Property Meander Belt Width Sinuosity through Time
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 18 1400717 004 R Rev1
Table 4 Belt Width of the Roaring Fork River at North Star
Year
Belt Width (ft)
Smith Property
North Star
Open Preserve
1893 363 306
1951 220 363
1958 200 370
1983 200 370
1999 225 370
2011 245 363
2014 295 311
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 19 1400717 004 R Rev1
4.0 EROSION CALCULATIONS
The purpose of the erosion calculation is to assess the potential for erosion for the streambed, vegetated
stream banks, and bare stream banks at the seven cross sections identified during the site visit in
July 2014. The likelihood of stream bank and bed erosion of the Roaring Fork River through North Star
Preserve was assessed using Annandale’s Erodibility Index Method (Annandale 2006). The methodology
accounts for both the erosive power of the water, as stream power, and the erosive resistance of the soil
material. The analysis was conducted as two components, the ability of water to erode, and the ability of
the earth materials to resist erosion. These two components are compared relative to each other and
interpreted relative to their significance to the balance of the fluvial system.
4.1 Stream Power Calculations
Stream power was calculated for straight reaches and at bends for the meandering Roaring Fork River
through North Star Preserve. The total stream power, Ptotal, can be expressed as: 𝑃𝑃𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡=𝑃𝑃𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡+𝑃𝑃𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡
Where Ptangential is the stream power due to flow in the longitudinal direction of the river and Ptransverse is the
stream power due to secondary flow in bends.
Odgaard’s (1986) Meander Flow Model is used to assess the flow and bed topography of a cross section
along a channel. The model is valid for steady, subcritical, turbulent flow in alluvial channel meanders
with uniform bed sediment and accounts for the development and decay of stream power through a bend.
Constraints of the model are that 1) the channel width is assumed to be constant, 2) the centerline radius
of curvature is assumed large compared to channel width, 3) flow depth is small compared to channel
width, 4) cross-sectional velocity components are small compared to down-channel components, and 5)
turbulence is isotropic. The definition sketch of a meander channel and cross section are provided in
Figure 17. The variables identified in Figure 17 are defined in the subsequent paragraphs.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 20 1400717 004 R Rev1
Figure 17 Definition Schematic of Channel Geometry and Hydraulic Variables (Odgaard 1986)
The method has been tested with field data and was found to provide accurate representation of the
streamwise and cross-sectional geometry of meandering rivers. The solution presented here is for
constant radius bends.
Model input parameters and their sources include:
Total discharge, Q, estimated from the 2-year storm event identified from the regression
curve for North Star in Figure 6
Median size of the bed material, D, from Wolman pebble counts conducted during the
site visit
Bed slope, So, averaged across the site from the SGM site thalweg survey conducted in
August 2014
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 21 1400717 004 R Rev1
Average water surface width, W, calculated based on the cross section profiles, bed
slope, and 2-year discharge event using Flowmaster software
Average flow depth, dc, from Flowmaster software output
Radius of the bend at the centerline, rc, estimated from the SGM August 2014 survey
Odgaard’s (1986) equation combines the input parameters to calculate the centerline and shear velocities
(uc and ustar, respectively), the transverse bed slope, Sf, for a given distance traveled along the curve, s,
and the expected maximum flow depth, dmax, along the outer edge of the channel.
The transverse bed slope changes as water travels around the curve and is dependent on the radius of
curvature of the bend, effective width of the channel, centerline and shear velocities, and bed material.
The variation in the transverse bed slope in the stream is calculated by dividing the stream reach into
straight and constant radius reaches, and identifying the starting point for each reach computation,
generally the point of inflection between adjacent bends, where the variation in transverse bed slope is
roughly equal to zero. The progression of transverse bed slope variation depending on the relationship
between the distance along the centerline, s, and the effective channel width, b as: σ = s/b. Figure 18
shows the change in transverse bed slope, sTc, with distance along the bend, s, for subsequent
downstream cross sections.
Figure 18 Transverse Bed Slope, sTc, as a Function of Distance, s, for Cross Section 2
uc Q
b dc⋅:=ustar g S0⋅dc⋅:=
0 100 200 300 4000
0.01
0.02
0.03
Perimeter Distance (ft)
Tr
a
n
s
v
e
r
s
e
B
e
d
S
l
o
p
e
a
t
r
c
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 22 1400717 004 R Rev1
The change in slope can be used to identify the maximum flow depth expected at a location at distance ‘𝑠𝑠’
along the meander. The tangential stream power can be calculated directly from the shear velocity as
shown below, where ρ is the density of water (Annandale 2006):
The transverse flow velocity and stream power are calculated using Chang’s (1988) relations. Transverse
velocity, v, is first calculated:
Where rc is defined as previously and theta is the angle of the arc defined by the beginning of the bend
and the location of the point of interest along the bend, as depicted in Figure 15. The tangential velocity
component u is estimated as the channel centerline velocity defined previously, the initial transverse
velocity vo is assumed equal to 0 ft/s, and F1 and F2 are coefficients based on the friction factor and von
Karman coefficient.
The transverse stream power is further calculated as a function of the radial distance outward from the
channel centerline, tangential and transverse velocities, u and v respectively, and the transverse bed
slope as follows:
Where dmax is the maximum calculated flow depth from Odgaard’s (1986) equation. The tangential and
transverse stream power values can be combined to calculate the total stream power acting on the
channel cutbank, or the tangential component can be used by itself to represent the stream power acting
on the channel bed. Tangential, transverse, and total stream power values were calculated at the location
of each cross section as well as at the location of the maximum flow depth around each meander on
which a cross section is located to gauge the highest stream power available. These values represent the
water’s ability to erode the bed and banks. In the following section, the ability of the banks to resist
erosion is assessed.
Ptangential 7.853 ρ⋅ustar3⋅:=
v exp F2 f()−rc theta⋅()⋅v0 F1 f()u⋅()rc theta⋅()⋅exp F2 f()rc⋅theta⋅()()
rc
⋅+
⋅:=
Ptransverse ρ v⋅()
rc
∆r⋅u()2⋅1 m1 f()+
m1 f()
2
⋅1
dmax()
2
m1 f()
⋅dmax()
1 2
m1 f()+
1 2
m1 f()+
⋅:=
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 23 1400717 004 R Rev1
4.2 Soil Erodibility Calculations
Annandale’s Erodibility Index Method has been used to assess the erosive resistance of the earth
materials based on the Erodibility Index, K, of the material: 𝐾𝐾=𝑀𝑀𝑡𝑡∙𝐾𝐾𝑏𝑏∙𝐾𝐾𝑑𝑑∙𝐽𝐽𝑡𝑡
Here Ms is the mass strength number, Kb is the block size number, Kd is the discontinuity bond shear
strength number, and Js is the relative ground structure number, equal to 1 for soils.
The mass strength number is a function of the material’s shear strength for cohesive soils and density for
non-cohesive soils. The higher the mass strength number, the greater the erosive resistance of the soil
material.
The block size number is a function of the material particle size. For intact cohesive soils, Kb is equal to
one. For non-cohesive or granular soils, Kb is related to the characteristic particle diameter (in meters) by
the following equation:
Where D equals the D50 (median diameter) of the armor layer, if present, or the D85 (particle diameter
below which 85% of soil particles are smaller) of the surface material if an armor layer can potentially
form. For this analysis, D was set equal to the D50 value for the bed and bank material based on soil
testing, where bare granular soils were present. For cases where vegetation was present and/or
assessed, D was set equal to the size of the vegetation root ball. Sizes and associated Kb values for
grass and willows are provided in Table 5 below:
Table 5 Root Ball Size
Vegetation Diameter in. (m) Kb
Grass 5.0 (0.127) 2.05
Willow 10.0 (0.254) 13.49
The discontinuity/inter-particle bond shear strength number, Kd, is estimated from the residual friction
angle of granular earth materials, as shown in the following equation, and is set equal to 1 for cohesive
materials.
Kb 1000 D3⋅:=
Kd tan φ():=
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 24 1400717 004 R Rev1
Annandale’s Erodibility Index, K value, can be related to stream power using the equation below, where
Pcrit is the critical stream power of the soil material.
when K ≤ 0.1
when K > 0.1
When the available stream power of the stream (Ptotal or Ptangential) exceeds the critical stream power,
erosion will occur.
4.3 Erosion Assessment
Field assessment collected and analyzed representative samples of the material that composes the bed
and banks. The methods presented above enable a comparison of the hydraulic forces along a meander
bend relative to the ability of the bed and bank materials to resist erosion or transport. In general, the
bankfull discharge has the potential to transport the material that lies on the bed of river, but the cohesion
provided by the presence of fine material and vegetation in the bank material makes the banks stable at
bankfull discharge. The stability of the channel geometry through time, as observed in the historical
changes in the channel position and characteristics, indicates that flows greater than bankfull discharge
would likely be needed to induce channel migration. This higher magnitude flow likely occurred prior to
the Transmountain Diversions. These higher magnitude discharge events can and do occur in the post
Diversion time, and this observation is confirmed by cutbank erosion, but they are significantly less
frequent. The transport of the bed material is also a logical result, as the conveyance of material delivered
from upstream through the site is needed to maintain the observed morphologic equilibrium.
4.4 Field Investigation
Golder conducted fieldwork at the North Star Nature Preserve from July 28 to 30, 2014. During field
assessment, the entire reach of the Roaring Fork within North Star was observed and photo documented
(Appendix A). The on-site head gates were identified and surveyed. Golder also collected soil samples of
the bed and bank materials (Appendix B).
Pcrit 0.48 K0.44⋅:=
Pcrit K0.75:=
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 25 1400717 004 R Rev1
5.0 DISCUSSION
5.1 Ecological significance
There is a documented transition occurring in the North Star Preserve from a hydric vegetation
community to a more mesic community. This trend indicates a shift in the local hydrology. While this could
be misinterpreted as being the result of the decrease in overbank flooding, Golder believes that this is not
the case for the following reasons:
1. The plant communities of the North Star Preserve are highly dependent upon the hillslope hydrology for the majority of their water supply.
2. The decrease in local water supply is most likely caused by localized ditching and channelization of floodplain surface water.
3. The fluvial hydraulics were likely to have been disconnected from the floodplain by natural processes prior to the late 1900s, and have not played a role in the water supply
needs of these plant communities from that time forward.
For these reasons, Golder recommends that North Star restoration efforts are focused on stabilizing the
wetland hydrology, rather than attempting to reconnect the fluvial hydraulics.
5.2 Role of the Trans-Mountain Diversions
The Independence Pass Transmountain Diversion System (IPTDS) plays a fundamental role in the
geomorphology of the North Star Preserve. The IPTDS diverted an annual average of 37,221 acre-feet
(37 percent) of the Upper Roaring Fork Sub-watershed from 1997 to 2005. While the amount of water
abstracted from the system varies through time, the majority of the abstraction takes place from May to
August when the highest magnitude of discharge occurs. In a typical year, the IPTDS extracts
approximately 38% of the total volume of the Upper Roaring Fork watershed (Clark et al. 2008).
The decrease in discharge values associated with the diversion of a portion of the upstream water has
likely decreased the rate of morphologic change and increased the potential for deposition for the site.
The decrease in the magnitude and timing of the high volume discharge events has also likely caused the
river to be disconnected from the floodplain. This disconnection occurs because the floodwaters no longer
access the over bank portion of the channel geometry as frequently as prior to the diversion. While
Golder is certain that this process is occurring, we do not believe that this is reason for the shift in
vegetation patterns from hydric to mesic. We believe that this ecological shift is taking place because of
the reduction floodplain water through the management of ditches, headgates, and surface water use by
adjacent landowners.
5.3 Morphologic Stability
Overall, the site appears to be a morphologically stable fluvial system controlled by the downstream
boundary condition provided by a terminal moraine. This assessment of stability does not imply that the
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 26 1400717 004 R Rev1
channel has remained in the same physical location, but that the characteristics of the channel geometry,
such as channel width, sinuosity, and meander belt width (see Section 3.3) have remained relatively
constant over time. This stability is likely enhanced by the abstraction of water by the Transmountain
Diversions.
5.4 Bank Erosion
While there is some bank erosion on the outside of the meander bends (Appendix A: Photographs 5, 6, 9,
13 and 14), the eroded bank material is likely deposited on the next downstream point bar (Appendix A:
Photographs 3, 9, and 15). The erosion and deposition is a natural process that is typical of
geomorphically active environments. This observation is supported by channel stability calculations that
indicate lateral erosion will occur at discharges greater than bankfull flow. Additionally, these cutbanks are
failing through undercutting allowing for the vegetated banktop to over-hang the river to provide fish
habitat, refugia, and cooler water temperatures.
The on-site willows and riparian vegetation help to fortify the bank, but if isolated, they are flanked by
stream flow (Appendix A: Photograph 6). Channel bifurcation is a natural process that can potentially
provide diverse habitat (Appendix A: Photograph 11). The riparian vegetation prevents access to the river
and can be used as a natural method for redirecting recreational activities. However, it is not
recommended that riparian vegetation be planted on every bank because, by stopping cutbank erosion,
the local sediment supply would be removed and the point bars would cease developing. Currently the
point bars provide excellent habitat for vegetative succession.
5.5 Headgates and Wetland Hydrology
The ditches and channel associated with the headgates (see Figure X) are the result of previous on-site
agricultural activity. While their original purpose was to lower the local groundwater table to facilitate hay
production and ranching, their continued effect is the likely source of the observed ecological transition.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 27 1400717 004 R Rev1
Figure 19 Headgate structure in North Star Preserve
5.6 In-Stream Structures
Previous investigations (Miller and Ayers 2001) have noted the presence of in-stream structures
consisting of placed riprap at multiple locations throughout the site. Many of these in-stream structures
appear to no longer be fulfilling their original intended purpose. The Miller and Ayers (2011) report
recommends removal and relocation of the materials. While Golder believes that this recommendation is
well intentioned, we recommend careful consideration prior to action. There are many potential benefits
and detriments that could come from this remedial action and its consequences should be assessed
relative to the long-term management goals.
5.7 The Smith Property
One location that appears to be threatened by bank erosion is the cottonwood trees on the Smith
Property (Appendix A: Photograph 13). The cut bank in this location is comprised of medium to coarse
sand that is eroding more quickly than other locations through the reach. As these cottonwoods are
important for the long-range ecological functionality and health of North Star, it is recommended that
localized bioengineering techniques be applied to the ensure the continued stability of the bank and
surrounding riparian vegetation.
5.8 Long-Term Channel Incision
While the recent past and predictable future of the North Star Nature Preserve are, in Golder’s
assessment, a stable morphology, in the larger context of geologic time, the Roaring Fork River and the
Rocky Mountains the channel is likely to incise into the surrounding landscape. This larger scale incision
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 28 1400717 004 R Rev1
is being inhibited initially by the moraine dam and recently by the Transmountain Diversion. While the
particles that make up the moraine are likely to be relatively stable, eventually the larger scale process of
incision will cause the dam to breach and the local channel to incise. The continued existence of the
North Star Nature Preserve as a wetland is dependent upon the stability of the moraine dam. It must also
be emphasized that the natural process of incision into the moraine is likely to be discouraged by the
Transmountian Diversion, and that cessation of the diversion could reactivate incision.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 29 1400717 004 R Rev1
6.0 CONCLUSIONS
The Roaring Fork River through the North Star Preserve is in a state of recently attained morphologic
stability with the artificially induced site conditions. The abstraction of a significant portion of the basins’
water supply by the Transmountain Diversion has decreased the transport capacity of the river to the
extent that it is no longer incising into the terminal moraine that defines the site hydrology and hydraulics.
This condition is likely to persist in the near term future, depending on the stability of the moraine dam
and the continued operation of the Transmountain Diversion. However, within the larger context of
geologic time, the Roaring Fork River is gradually incising. In the future, this long-term incision and the
local control of the site hydrology may interfere with one another in the form of further incision into the
moraine dam.
While it is likely that the reduced discharge induced by the Transmountain Diversion has decreased the
connection of the river to it floodplain, Golder believes that this disconnection may have already taken
place in the form of incision through the moraine dam long before any anthropogenic activities occurred.
The morphologic shift from the state of equilibrium represented by the preserved meanders in the form of
oxbow lakes to the modern channel is a result of the gradient increase caused by the moraine incision.
This morphologic shift is accompanied by the disconnection of the modern channel from the floodplain.
Reestablishing this connection under the post Transmountian Diversion hydrologic regime would likely
require significant alteration to the landscape. This alteration could have potentially negative
consequences to the existing flora and fauna that comprise the local ecology.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 30 1400717 004 R Rev1
7.0 RECOMMENDATIONS
The key recommendations for North Star:
Develop a plan to stabilize the groundwater table within the onsite wetland
Eliminate the adjustability of the headgates
Potentially infill onsite drainage channels.
Understand implications of potential new projects.
− There is the potential for nearby projects to change the hydrologic features of the North Star Preserve. If these new projects interact with the site
hydrology, they may negatively affect conditions within the Preserve.
− Golder recommends that the planned future actions of nearby sites be
assessed for their potential impact to the Preserve.
Investigate the potential for the enhancement of beaver habitat to facilitate sediment
retention in the floodplain channels.
Install biostabilization bank protection to decrease the potential for the destruction of the
habitat provided by the mature cottonwood stand on the Smith property.
This biostabilization will need to be designed to match the hydraulic conditions that
the site is likely to experience and consist of local site-specific native vegetation.
Carefully consider the removal, or modification, of the existing in stream structures.
Modification of the existing in stream structures could have a significant effect on the channel morphology and existing habitat. Golder recommends that potential changes
be assessed with hydraulic modeling prior to removal or modification.
Monitor downstream channel elevation
Incision of the channel into the moraine dam may result in significant changes to the site.
Potential changes can be assessed via repeated high resolution surveying efforts similar to the one conducted as part of this investigation, or repeated Lidar surveys.
If incision is observed at the moraine, further action will likely be required.
Efforts to modify the landscape to reconnect the fluvial hydrology to the existing
floodplain could require substantial modification to the site topography that would likely disturb the existing ecology.
These potential modifications could have detrimental effects to the existing ecological resources.
Golder believes that the hydrology of the adjacent floodplain is currently controlled by the hillslope and the wetland hydrology, and not the fluvial hydrology.
The discharge of the river has been significantly reduced by the construction of the Transmountain Diversion. Modification of the landscape to facilitate the more
frequent occupation of the floodplain by the modern hydrologic regime would require substantial disturbance to the landscape.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 31 1400717 004 R Rev1
GOLDER ASSOCIATES INC.
Amanda J. Rock Robert P. Humphries Staff Geological Engineer Senior Project Fluvial Geomorphologist
Randy H. Mandel Senior Restoration Ecologist/Project Manager
AJR/RPH/RHM/rjg
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
October 2014 32 1400717 004 R Rev1
8.0 REFERENCES
Annandale, G.W. 2006. Scour Technology: Mechanics and Engineering Practice. McGraw-Hill, New York,
NY.
Bryant, B. 1979. Geology of the Aspen 15-minute Quadrangle, Pitkin and Gunnison Counties, Colorado, U.S. Geological Survey Professional Paper 1073, Washington, DC. http://pubs.usgs.gov/pp/1073/report.pdf.
Chang, H.H.1988. Fluvial Processes in River Engineering. Wiley, Hoboken, NJ.
Clark, S., et al. 2008. State of the Roaring Fork Watershed Report, Roaring Fork Conservancy.
November.
Gringorten, I.I. 1963. A Plotting Rule for Extreme Probability Paper, Journal of Geophysical Research, Vol. 68, No. 3, February, pp. 813-814.
Gumbel, E.J. 1958. Statistics of Extremes. Columbia University Press, New York, NY.
Hickey, A., J.C. Emerick, and K.E. Kolm. 2000. Preliminary Hydrologic and Biological Characterization of the North Star Nature Preserve, Pitkin County, Colorado, Submitted to the Pitkin County Board of
Commissioners and the Aspen City Council.
Klasz, G., W. Reckendorfer, and D. Gutknecht. 2012. Morphological aspects of bankfull and effective discharge of gravel-bed rivers and changes due to channelization. In 9th International Symposium on
Ecohydraulics 2012, Proceedings.
Kolm, Kenneth E., and Paul K.M. Heijde. 2011. Hydrologic and Environmental Systems Analysis and Formulation of Conceptual Models for the Central Roaring Fork Tributaries (CRFT), Pitkin County, Colorado. Phase 1 of the Development of County-wide Maps for GIS-Based Groundwater Resources
Evaluation, Pitkin County, Colorado. Prepared for Pitkin County Health Rivers Board and Board of County Commissioners. May 25.
Leopold, L.B., Wolman, M.G., and Miller, J.P. 1964. Fluvial Processes in Geomorphology. New York.
Miller and Ayers. 2011. Final Letter Report – Geomorphic Assessment of the Roaring Fork River and Impacts of Groundwater Changes on Wetlands, North Star Nature Preserve, Pitkin County, Colorado, Ft. Collins, CO, December 14.
Odgaard, A.J. 1986. Meander Flow Model I: Applications, Journal of Hydraulic Engineering, Vol. 112, No. 12, December, ASCE, pp. 1136-1150.
Odgaard, A.J. 1986. Meander Flow Model I: Development, Journal of Hydraulic Engineering, Vol. 112,
No. 12, December, ASCE, pp. 1117-1136.
Roaring Fork Conservancy. 2008. State of the Roaring Fork Watershed Report 2008. Sponsor Tuedi Water & Power Authority. Chapter 4.1.
Wohl. T. 2008. The Effect of Bedrock Jointing on the Formation of Straths in the Cache la Poudre River Drainage, Colorado Front Range, Journal of Geophysical Research, Vol. 113, No.1, January.
Wolman, M.G. 1954. A Method of Sampling Coarse River-Bed Material. Transactions of the American
Geophysical Union 35(6):951-956.
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 PitkinOST_NorthStar 17OCT14.docx
APPENDIX A PHOTO LOG
October 2014 1 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 1
Riprap placed on bank immediately downstream of
Stillwater Road
PHOTO 2
Riprap placed on bridge piers
at Stillwater Road
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 2 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 3
Typical point bar succession
PHOTO 4
In-stream structure located down gradient of head gate
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 3 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 5
Typical eroding cutbank
PHOTO 6
Typical eroding cutbank Note
how the willow has been flanked
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 4 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 7
Streambank was historically
colonized by willows
PHOTO 8
This area is known as “the beach” and provides access to
the river Note the sand material was historically
imported
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 5 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 9
Typical cutbank in the background with the aggrading
point bar in the foreground
PHOTO 10
Willow cuttings from beaver activity
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 6 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 11
Beaver building small dam on a “flanked” willow on the
mainstem
PHOTO 12
Large woody debris near the paraglide landing
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 7 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 13
Large cottonwood trees that may be threatened with
continued cutbank erosion
PHOTO 14
Active cutbank on the Smith Property
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 8 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 15
Actively-forming point bar on
the Smith Property
PHOTO 16
Farthest upstream point
examined on the Smith Property
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
October 2014 9 1400717 004 R Rev1
Appendix A
Pitkin County / Ecological Services for Open Space and Trails
PHOTO 17
Active beaver run
I:\14\1400717\0400\004 R Rev1\1400717 004 R Rev1 App-A PhotoLog.docx
APPENDIX B SOIL SAMPLES
October 2014 Soil Samples 1400717 004 R Rev1 Appendix B
The soil samples were taken along the bed and bank of the Roaring Fork River (Figure B-1).
Figure B-1: Cross Section and Sediment Sample Locations for the North Star Nature Preserve
I:\14\1400717\0400\004 R Rev1\AppB\1400717 004 R Rev1 App-B SoilSamples.docx
October 2014 Soil Samples 1400717 004 R Rev1 Appendix B
NRCS Soils groups these soils into three soil types, all of which are loams (Figure B-2):
Figure B-2: Soils Map (Aspen-Gypsum Area, Colorado, Parts of Eagle, Garfield, and Pitkin
Counties (CO655)
The Golder soils laboratory tested the bank samples and produced the following figures. The Wolman
Pebble Count method (Wolman 1954) was used to develop gradations for the bed materials.
Map Symbol
76 = Mine loam, 12 to 25 percent slopes 77 = Mine loam, 25 to 65 percent slopes 92 = Redrob loam, 1 to 6 percent slopes
120 = water
I:\14\1400717\0400\004 R Rev1\AppB\1400717 004 R Rev1 App-B SoilSamples.docx
1400717.1
PROJECT NAME:Pitkin Cnty/Ecological Svcs/CO
SAMPLE ID:XS2 DEPTH (ft):--
TYPE:Bag
Sieve % Passing
3-in 75.0 100.0 Description Percentage
2-in 50.0 100.0
1.5-in 37.5 100.0
1-in 25.0 100.0
3/4-in 19.0 100.0
3/8-in 9.5 100.0
#4 4.75 100.0
#10 2.00 99.2 Coarse Sand 0.79
#20 0.850 98.9
#40 0.425 98.5
#60 0.250 98.2
#100 0.150 97.4
#200 0.075 92.2
0.031 74.4
0.020 60.5
0.012 46.4
0.009 38.9
0.006 33.3 LL PL PI
0.003 24.6 ------
0.001 16.6
----
Notes:
TECH RJM
DATE 8/4/2014
REVIEW MB
USCS Group SymbolAs-Received Moisture Content (%)Visual Description (Golder Procedure):
Fine Gravel
Medium Sand
Fine Sand
0g of particles up to 4.75mm maximum size were removed from particle size analysis sample prior to testingParticle size analysis sample mechanically dispersed using Stirring Apparatus A for about 1 minute
SILTY CLAY, trace organics, dark yellowish
brown, moist
August-14
Hy
d
r
o
m
e
t
e
r
A
n
a
l
y
s
i
s
Fines 92.23
6.31
PARTICLE SIZE DISTRIBUTION & ATTERBERG LIMITS
ASTM D421, D422, D4318
Coarse Gravel 0.00
Sie
v
e
A
n
a
l
y
s
i
s
(I
n
i
t
i
a
l
S
e
p
a
r
a
t
i
o
n
o
n
N
o
.
4
S
i
e
v
e
)
Particle Size
(mm)
0.00
0.67
2-in 1.5-in 1-in 3/4-in 3/8-in #4 #10 #20 #40 #60 #1003-in #200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110100
Pe
r
c
e
n
t
P
a
s
s
i
n
g
Particle Size (mm)
0
10
20
30
40
50
60
0 102030405060708090100110
Pl
a
s
t
i
c
i
t
y
I
n
d
e
x
(
P
I
)
Liquid Limit (LL)
CH or OH
MH or OH
CL or OL
ML or OLCL - ML
U-Line A-line
1400717.1
PROJECT NAME:Pitkin Cnty/Ecological Svcs/CO
SAMPLE ID:XS4 DEPTH (ft):--
TYPE:Bag
Sieve % Passing
3-in 75.0 100.0 Description Percentage
2-in 50.0 100.0
1.5-in 37.5 100.0
1-in 25.0 100.0
3/4-in 19.0 100.0
3/8-in 9.5 100.0
#4 4.75 100.0
#10 2.00 99.7 Coarse Sand 0.33
#20 0.850 99.1
#40 0.425 98.1
#60 0.250 94.0
#100 0.150 77.6
#200 0.075 62.9
0.032 56.0
0.021 47.8
0.012 38.3
0.009 33.1
0.006 28.4 LL PL PI
0.003 20.3 ------
0.001 13.9
----
Notes:
TECH RJM
DATE 8/4/2014
REVIEW MB
August-14
Hy
d
r
o
m
e
t
e
r
A
n
a
l
y
s
i
s
Fines 62.89
35.22
PARTICLE SIZE DISTRIBUTION & ATTERBERG LIMITS
ASTM D421, D422, D4318
Coarse Gravel 0.00
Sie
v
e
A
n
a
l
y
s
i
s
(I
n
i
t
i
a
l
S
e
p
a
r
a
t
i
o
n
o
n
N
o
.
4
S
i
e
v
e
)
Particle Size
(mm)
0.00
1.56
USCS Group SymbolAs-Received Moisture Content (%)Visual Description (Golder Procedure):
Fine Gravel
Medium Sand
Fine Sand
___ g of particles up to ____ maximum size were removed from particle size analysis sample prior to testingParticle size analysis sample mechanically dispersed using Stirring Apparatus A for about 1 minute
SILTY CLAY and SAND, trace organics, dary
yellowish brown, moist
2-in 1.5-in 1-in 3/4-in 3/8-in #4 #10 #20 #40 #60 #1003-in #200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110100
Pe
r
c
e
n
t
P
a
s
s
i
n
g
Particle Size (mm)
0
10
20
30
40
50
60
0 102030405060708090100110
Pl
a
s
t
i
c
i
t
y
I
n
d
e
x
(
P
I
)
Liquid Limit (LL)
CH or OH
MH or OH
CL or OL
ML or OLCL - ML
U-Line A-line
1400717.1
PROJECT NAME:Pitkin Cnty/Ecological Svcs/CO
SAMPLE ID:XS6 DEPTH (ft):--
TYPE:Bag
Sieve % Passing
3-in 75.0 100.0 Description Percentage
2-in 50.0 100.0
1.5-in 37.5 100.0
1-in 25.0 99.2
3/4-in 19.0 98.5
3/8-in 9.5 79.8
#4 4.75 58.6
#10 2.00 45.7 Coarse Sand 12.98
#20 0.850 33.5
#40 0.425 19.8
#60 0.250 8.1
#100 0.150 4.1
#200 0.075 2.4
0.036 2.3
0.023 2.1
0.013 1.8
0.010 1.6
0.007 1.3 LL PL PI
0.003 1.0 ------
0.001 0.6
--SP
Notes:
TECH RJM
DATE 8/4/2014
REVIEW MB
August-14
Hy
d
r
o
m
e
t
e
r
A
n
a
l
y
s
i
s
Fines 2.41
17.35
PARTICLE SIZE DISTRIBUTION & ATTERBERG LIMITS
ASTM D421, D422, D4318
Coarse Gravel 1.50
Sie
v
e
A
n
a
l
y
s
i
s
(I
n
i
t
i
a
l
S
e
p
a
r
a
t
i
o
n
o
n
N
o
.
4
S
i
e
v
e
)
Particle Size
(mm)
39.86
25.89
USCS Group SymbolAs-Received Moisture Content (%)USCS Description (ASTM D 2487):
Fine Gravel
Medium Sand
Fine Sand
___ g of particles up to ____ maximum size were removed from particle size analysis sample prior to testingParticle size analysis sample mechanically dispersed using Stirring Apparatus A for about 1 minute
Poorly graded sand with gravel, brownish yellow,
moist
2-in 1.5-in 1-in 3/4-in 3/8-in #4 #10 #20 #40 #60 #1003-in #200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110100
Pe
r
c
e
n
t
P
a
s
s
i
n
g
Particle Size (mm)
0
10
20
30
40
50
60
0 102030405060708090100110
Pl
a
s
t
i
c
i
t
y
I
n
d
e
x
(
P
I
)
Liquid Limit (LL)
CH or OH
MH or OH
CL or OL
ML or OLCL - ML
U-Line A-line
1400717.1
PROJECT NAME:Pitkin Cnty/Ecological Svcs/CO
SAMPLE ID:XS7 DEPTH (ft):--
TYPE:Bag
Sieve % Passing
3-in 75.0 100.0 Description Percentage
2-in 50.0 100.0
1.5-in 37.5 100.0
1-in 25.0 100.0
3/4-in 19.0 100.0
3/8-in 9.5 100.0
#4 4.75 100.0
#10 2.00 99.3 Coarse Sand 0.70
#20 0.850 98.6
#40 0.425 97.5
#60 0.250 94.4
#100 0.150 83.9
#200 0.075 62.1
0.032 45.2
0.021 36.5
0.013 28.2
0.009 24.0
0.006 20.4 LL PL PI
0.003 14.3 ------
0.001 10.2
----
Notes:
TECH RJM
DATE 8/4/2014
REVIEW MB
USCS Group SymbolAs-Received Moisture Content (%)Visual Description (Golder Procedure):
Fine Gravel
Medium Sand
Fine Sand
___ g of particles up to ____ maximum size were removed from particle size analysis sample prior to testingParticle size analysis sample mechanically dispersed using Stirring Apparatus A for about 1 minute
CLAYEY SILT, trace organics, slight plasticity,
olive brown, moist
August-14
Hy
d
r
o
m
e
t
e
r
A
n
a
l
y
s
i
s
Fines 62.13
35.39
PARTICLE SIZE DISTRIBUTION & ATTERBERG LIMITS
ASTM D421, D422, D4318
Coarse Gravel 0.00
Sie
v
e
A
n
a
l
y
s
i
s
(I
n
i
t
i
a
l
S
e
p
a
r
a
t
i
o
n
o
n
N
o
.
4
S
i
e
v
e
)
Particle Size
(mm)
0.00
1.79
2-in 1.5-in 1-in 3/4-in 3/8-in #4 #10 #20 #40 #60 #1003-in #200
0
10
20
30
40
50
60
70
80
90
100
0.0010.010.1110100
Pe
r
c
e
n
t
P
a
s
s
i
n
g
Particle Size (mm)
0
10
20
30
40
50
60
0 102030405060708090100110
Pl
a
s
t
i
c
i
t
y
I
n
d
e
x
(
P
I
)
Liquid Limit (LL)
CH or OH
MH or OH
CL or OL
ML or OLCL - ML
U-Line A-line
Golder Associates Inc.
44 Union Boulevard, Suite 300
Lakewood, Colorado 80228 USA
Tel: (303) 980-0540
Fax: (303) 985-2080
Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation