Geospatial Inventory and Assessment of Sediment from Unpaved Roads
in the Dry Fork Creek Watershed
Sub-basin of the Kings River Watershed
Prepared For
The Nature Conservancy (TNC)
August 30, 2005
By the
Watershed Conservation Resource Center (WCRC)
Project Team
Matthew Van Eps and Sandi Formica, WCRC
Doyle Crosswhite and Ethan Inlander, TNC
Introduction
The Kings River watershed, in Northwest Arkansas, is uniquely diverse both geographically and
ecologically. The Nature Conservancy’s (TNC) Ozarks Ecoregional Conservation Assessment
identified the Kings River as containing a significant concentration of aquatic biodiversity. It is
the last unimpounded tributary of the White River and hosts thirty endemic species including the
Winter Stonefly (Allocapnia ozarka). Also TNC has identified sedimentation as a principal
stressor (TNC, 2003). Unpaved roads have the potential to be a significant source of suspended
sediment in rural watersheds, and the sediment from these roads may impact many species in the
Kings River watershed. Even during small rainfall events, storm water runoff from unpaved
roads and ditches can contribute suspended sediment to streams and creeks resulting in elevated
turbidity and total suspended solids concentrations. Suspended sediment loads impact aquatic
habitats by filling interstitial spaces of the gravel stream bed and by clogging fish gills and
suffocating eggs and benthic insect larvae.
TNC contracted with the Watershed Conservation Resource Center (WCRC) to evaluate
unpaved roads in the Dry Fork Creek watershed, a sub-basin of the Kings River watershed
(Figure 2). Matthew Van Eps of the WCRC managed the collection of the field data and
geospatial inventory, developed final maps, conducted sediment modeling, developed the
sediment reduction recommendations, and compiled the final report. Sandi Formica of the
WCRC provided overall management of the project and assisted with the development and
technical review of the report. Doyle Crosswhite of TNC coordinated TNC staff and
equipment; coordinated with local watershed representatives, and assisted with field data
collection. Ethan Inlander of TNC prepared field maps, helped to customize data logging
menus, and assisted with field data collection. Duane Coatney, Carroll County Justice of the
Peace, also assisted with field data collection. Information contained in this report was
presented to local, state and federal representatives and other members of the public during a
workshop hosted and coordinated by TNC on July 26-27, 2005. Mike Hanley of TNC and Ron
Redmon of the Arkansas Natural Resources Commission provided expertise during indoor and
field sessions of the workshop.
The WCRC evaluated 60.6 miles of
unpaved roads in the Dry Fork Creek
watershed. The project included two
primary elements: 1) development of a
GIS based inventory of unpaved road
conditions and 2) estimation of sediment
loads from unpaved roads entering the
stream network using the U.S. Forest
Service Water Erosion Prediction Project
(WEPP) road model. The inventory data
was collected April 19th - 22nd, 2005.
The field data required to perform the
WEPP modeling was collected May 12th,
13th, and 25th, 2005 (Figure 1).
Figure 1. Collection of field data for WEPP modeling
1
Figure 2. Dry Fork Creek watershed, Northwest Arkansas
2
Unpaved Roads Geospatial Inventory
The roads inventory is a compilation
of road condition data for publicly
owned unpaved roads in the Dry
Fork Creek watershed. The
inventory can be used to assist in the
development of a "best management
practices (BMP)" implementation
plan for improving unpaved roads
and reducing sediment delivery to the
stream network. Vehicle mounted
Trimble GPS receivers with Trimble
XT data logging devices were used
to collect information on a variety of
road attributes (Attachment 1).
Attributes evaluated were selected
based on work performed by the U.S.
Forest Service (USFS), Ouachita
Figure 3. Collection of road inventory data using GPS equipment
National Forest, in Hot Springs,
Arkansas (Clingenpeel, 2004). Road conditions were logged as attributes in a GPS file that was
generated using Trimble XT units and Pathfinder Office software (Figure 3). Both line and point
GIS feature data were collected for analysis. Line features included attributes such as road
surface substrate type, presence and condition of ditches and ruts, and the presence of berms.
Line feature data were used to evaluate the general road network. The line feature data were also
used to extrapolate the results of the WEPP modeling of randomly selected road segments to the
portions of the road network that were not modeled. Point features included the locations of
bridges, culverts, cross-drains, wing-ditches, fords, and low-water crossings.
Inventory Results and Recommendations
The Dry Fork Creek watershed has a watershed area of approximately 54 mi2 (Table 1). The
GPS inventory included 60.6 miles of publicly owned unpaved roads. Using this information
along with existing Arkansas
Highway and Transportation
Table 1. Summary of unpaved roads in the Dry Fork Creek watershed
Department (AHTD) GIS files
Dry Fork Creek
and the 2002 Digital Orthophoto
Watershed
Quarter Quadrangles (DOQQs),
2
Watershed Area (mi )
54.0
the length of privately owned
unpaved roads was estimated to
Unpaved Roads
be 43.0 miles. The distribution
Publicly Owned (mi)
60.6
or density of unpaved roads (road Privately Owned (mi)
43.0
Total
103.6
miles divided by watershed area)
in the Dry Fork Creek watershed
Road Density
is also shown in Table 1. The
Publicly Owned (public) (mi/mi2)
1.1
publicly owned unpaved road
2
Public
and
Private
(mi/mi
)
2
1.9
density was 1.1 mi/mi , and
3
considering both public and private unpaved roads, the total unpaved road density was 1.9
mi/mi2. The Dry Fork Creek watershed has a slightly higher publicly owned unpaved road
density when compared to the density of 0.9 mi/mi2 in the North Big Creek watershed, a subbasin of the Strawberry River watershed in Northeast Arkansas (WCRC, 2005). The difference
may be due to the proximity of the Dry Fork Creek watershed to the large population center of
Northwest Arkansas.
Line Features of Publicly Owned Unpaved Roads:
Inventoried roads were classified as the following road types: single lane, double lane, and twotrack. The single lane road type represented 94% of the total number of inventoried road miles
in the Dry Fork Creek watershed.
Road surface materials were noted and categorized into three general types: gravel, spot, and
native. Gravel surfaces were those where a significant portion of the road surface was composed
of imported materials. Spot surfaces were those that had both imported and native materials.
Native surfaces were those surfaces that were primarily composed of the local soil type. Of the
60.6 miles inventoried, 67% were spot surfaced, 24% were gravel surfaced, and 9% miles were
native surface.
Figure 4. County Road 2360 near Madison – Newton County line
The presence of ditches on inventoried roads was noted with 87% or 52.5 miles having a ditch on
at least one side of the road. The depth of ditch erosion was observed and placed into three
categories: minimal erosion, one to 12 inches, and greater than 12 inches. Sixty-four percent or
4
33.7 miles of the roads with road-side ditches were found have an erosion depth between one and
12 inches (Attachment 2). The erosion depth was observed to be greater than 12 inches for 22%
or 11.8 miles. Severely eroding ditches were generally located on steep road grades and should
be considered priorities for BMP implementation. Particular road segments identified as having
severe ditch erosion include County Roads (CR) 943 and 3 in Carroll County, CR 2645 (Figure
9) in Madison County, and portions of CR 943 in Newton County. These road segments are
further discussed in the sediment reduction priorities section of this report.
The establishment of vegetation or other ditch lining as a BMP in road-side ditches can
potentially reduce water velocities, ditch erosion, and sediment delivery to receiving streams.
The presence of vegetation or ditch lining was recorded. Generally, few of the road-side
ditches had any type of vegetation or ditch lining, and of the 52.5 miles of roads with ditches,
only 7% were vegetated.
Road surface erosion was noted as potholes, wash-boarding, rill erosion, and longitudinal tire
ruts. Sites with multiple potholes, rill erosion, or wash-boarding were identified and cataloged
as point features. Road segments with tire ruts were recorded as line features and the depth of
the ruts was recorded. Identification of the areas with significant surface erosion can be used to
determine road segments that need to be reshaped, or where BMPs need to be implemented to
reduce surface erosion and the frequency of maintenance. There were 30 sites where numerous
potholes had formed, 23 sites where rill erosion was occurring, and three sites where washboarding was taking place. A total of 3.2 miles of unpaved road had ruts that were between two
and six inches in depth (Attachment 3).
Figure 5. County Road 1505 near Carroll – Madison County line
5
The formation of berms is generally the result of road maintenance activities where the surface
material graded from the road is pushed to the side and forms a barrier to lateral water flow.
Berms do not allow water to drain from the road surface and increase the potential for surface
erosion and rutting. Berms are also a source of sediment as surface runoff erodes the
unconsolidated materials that make up the berm. Periodic removal of these berms could reduce
the amount of erosion and provide base material for road maintenance. There were several
areas in the Dry Fork Creek Watershed that had very large berms formed on the road-side;
specifically, CR 1505 (Figure 5) near the Madison – Carroll county boundary, CR 518
approaching CR 545, and CR 3 approaching Dry Fork Creek. Of the 60.6 miles of inventoried
unpaved roads, 26.6 miles or 44% had berms present.
Point Features of Publicly Owned Unpaved Roads:
Locations of point features, such as, stream crossings, wing-ditches, cross-drains, culverts, and
bridges were collected during the inventory. Attributes of point features can be found in
Attachment 1.
Table 2. Summary of stream crossings in the Dry Fork
A total of 77 stream crossings were
Creek watershed
observed during the unpaved road
Dry Fork Creek
inventory. Based on watershed area,
Watershed
there were approximately 1.4 stream
2
54.0
Watershed
Area
(mi
)
crossings for each square mile. Stream
crossings are shown in Attachment 4 and
Stream Crossing Type
are denoted as slab, ford, culvert, or
8
Slab
bridge (Table 2). During the inventory,
17
Ford
it was observed that many road segments
42
Culvert
drained surface runoff directly to the
10
Bridge
stream network at these crossings.
Sediment from road segments that
traverse stream crossings would be
Number of Publicly Maintained
77
Stream Crossings
reduced if wing-ditches were installed
upslope from stream crossings. Also of
Stream Crossings to Watershed
1.4
concern, slab, ford, and culvert stream
Area Ratio
crossings can act as potential fish
passage barriers if not properly constructed and maintained.
There were a total of 8 slab type stream crossings observed during the unpaved road inventory.
Slab crossings with drops at the inlet or outlet that were at least six inches or greater present a
potential fish passage barrier (Attachment 5). Specific issues associated with observed slab-type
stream crossings include:
 There were two slab crossings over Tan Yard Branch that may pose a fish passage barrier
for migrating species. One slab is located on CR 720 and the other on CR 728. The
crossing on CR 728 has no culverts resulting in downstream scour and significant
upstream deposition (Figure 6).
 The slab crossing on CR 943 in Newton County over the southeast fork of Dry Fork
Creek, known as Hamstring Hollow, is a potential fish passage barrier. The number and
6

size of culverts appeared to be too few and
too small to adequately pass even moderate
flows. This has resulted in frequent overtopping and downstream scour.
The slab crossing on CR 943 in Newton
County over the southwest fork of Dry Fork
Creek, known as Sugar Camp Hollow, has a
drop greater than 12 inches and is a potential
fish passage barrier.
There were a total of 42 culvert stream crossings
identified during the unpaved road inventory. The
data collected included maintenance needs in addition
to fish passage barrier potential. Nine culverts were
identified as having an inlet or outlet drop of at least
six inches or greater; presenting a potential fish
passage barrier (Attachment 5). Culvert condition
(percent blockage) is shown in Attachment 6. A
summary of adverse conditions for selected culvert
stream crossings are described as follows:


Two completely blocked culvert crossings
Figure 6. Slab-type stream crossing on
were identified, one on CR 720 and another
County Road 728 in Carroll County
on an un-numbered road in the northeast
portion of the watershed.
Other culverts in need of maintenance include:
o Two culverts on CR 939 were more than 80% blocked and are in need of
replacement,
o A culvert on Dripping Springs Road (CR 524) near the spring is 85% blocked and
needs cleaning,
o Many culverts on CR 720 were at least 50% blocked and several culverts need
replacement,
o A culvert on CR 943 in Newton County was 75% blocked, and
o A culvert on CR 524, west of CR 550, was 65% blocked and needed replacement.
There were a total of 10 bridge stream crossings identified during the inventory (Attachment 4).
These bridges were generally in good condition and did not present immediate environmental
concerns. A general recommendation applicable to all bridges would be to install wing-ditches
up-gradient of the bridges, to prevent road and ditch runoff from directly entering receiving
streams. This recommendation is especially true for the bridges located on CR 3 at Dry Fork
Creek, CR 727, CR 720 at North Fork, and CR 943 at Brown Hollow.
A total of 17 low-water fords, either armored or natural, were identified in the inventory area
(Attachment 4). The primary issues observed with low water fords include berms formed from
loose materials generated during grading being placed in the wetted area of the ford and a
general lack of wing-ditches to prevent direct discharge of road and ditch runoff into streams.
7
There were many fords that drained both springs and small tributaries on CR 518 that could be
treated with wing-ditches to prevent direct discharge of sediment to the stream network.
Wing-ditches (also known as "water turn-outs" or "tail ditches") and cross-drains are the primary
mechanisms for diverting road and ditch runoff to a buffer area. A total of 679 wing-ditches
were identified. Several water diverting formations that would be best described as openings
created in road-side berms, or “push outs”, were observed and included in the wing-ditch
category. One hundred eighteen of the wing-ditches observed were these types of diversion
formations. The wing-ditch condition was recorded as open, partially blocked, or blocked
(Attachment 7). Eight percent of the wing-ditches were found to be blocked and nonfunctioning. Also, 8% of the wing-ditches were partially blocked. Blockage was typically the
result of graded road material being pushed into the wing-ditches during maintenance. Ensuring
that wing-ditches remain open after grading will improve road drainage, help to control road
erosion, and reduce sediment delivery to surface waters. Wing-ditches that are properly
positioned and installed should not drain directly to receiving waterbodies. Wing-ditches should
drain to a vegetated buffer and induce settling of sediments prior to reaching surface waters. A
map showing the location of wing-ditches that discharge directly to streams can be found in
Attachment 8. Wing-ditches that drain directly to surface waters should be moved upslope from
receiving waters to increase sediment filtration prior to entering the stream network.
The number of wing-ditches was insufficient on many of the steeper sloped road segments. This
frequently resulted in significant erosion in road-side ditches. The Arkansas Forestry
Commission recommends wing-ditch spacing of 200 feet, for roads with grades less than 5%,
every 100 feet for roads with grades between 5 and 10%, and every 75 feet for roads with slopes
greater than 10% (AFC, 2002). General locations where installation of additional wing-ditches
would serve to reduce erosion and required road maintenance were identified and are shown in
Attachment 7. These locations were identified by considering the local road grade, areas where
the road grade exceeded 10% (based on a DEM analysis), and the presence of inventoried wingditches. In addition to these identified areas, there were many other locations within the Dry
Fork Creek watershed that would benefit from the installation of additional wing-ditches.
Generally, installation of additional wing-ditches would be beneficial for road segments where
ditch erosion was greater than 12 inches.
Cross-drains are a critical component of an effective road and ditch runoff diversion system. The
purpose of the cross-drain is to move water away from the road prism. This is accomplished by
utilizing a culvert to move water from the ditch on the upslope side of a road to the downslope
side of the road for dispersion. Ditch blocks are components of effective cross-drain systems
that force water from the road-side ditch into the cross-drain culvert. The presence or lack of
ditch blocks associated with cross-drains was cataloged. A total of 40 cross-drains were
identified during the inventory, and 27 of the 40 did not need a ditch-block. This indicates that
most cross-drains were located at low-points of road segments rather than on the steeper sloped
portions of road segments, where they are most needed. Ditch blocks were not present at one of
the cross-drains where the use of a ditch block was appropriate. Blocked cross-drains are not
effective in moving water out of the ditch system. A total of 19 or nearly 50% of observed crossdrains in the watershed were partially or totally blocked (Attachment 9). Cross-drains that were
blocked should have the debris removed to maximize the efficiency of the drainage system.
8
Areas that would greatly benefit from the installation of cross-drains include CR 943 in Carroll
County where the road parallels Dry Fork Creek and CR 2645 in Madison County where severe
road-side ditch erosion is occurring.
Estimate of Sediment Production and Delivery from Unpaved Roads
Sediment production and delivery from unpaved roads in the Dry Fork Creek watershed was
estimated using the web-based WEPP: Road model (Elliot, 2004). The WEPP: Road model is
one in a series of the USDA Forest Service's internet-based computer programs based on the
Agricultural Research Service's Water Erosion Prediction Project (WEPP) model. An example
of the input screen for modeling individual road segments is shown as Attachment 10.
WEPP: Road Model Input Data
To perform the WEPP: Road model analysis, a detailed field survey was conducted during
which, data was collected on 10% of the unpaved road segments identified during the publicly
owned unpaved road inventory. Road segments were stratified by designed road width and
degree of erosion occurring in the road-side ditches. The generalized road design width used for
the development of road groups was “single,” roads designed to only pass one car at traveling
speed, and “double,” roads designed to pass two cars at traveling speeds. The number of
“double” width road segments was small; therefore, all of the “double” width roads were
consolidated into one group, regardless of the degree of road-side ditch erosion, for the purposes
of this evaluation. The numbers of two-track road types were very small in the inventoried area
and treated as single lane width roads. Road-side ditch erosion categories included erosion
greater than 12 inches, erosion
Table 3. Summary of road groups surveyed for WEPP: Road
between one and 12 inches, and
modeling analysis
minimal erosion (erosion less
Length
Road Group
than one inch). This approach
Count
Surveyed
(Road Width, Ditch Erosion)
yielded five road group types
(mi)
Double Lane
2
1.2
(Table 3). Ten percent of road
Single
Lane,
No
Ditch
6
0.4
segments from each group were
Single
Lane,
Ditch
Erosion
>
12"
10
1.7
selected using the random
Single Lane, Ditch Erosion 1-12"
17
4.0
number generator in Microsoft
Single Lane, Ditch Erosion < 1"
4
0.5
Excel. The road segments
included in the detailed survey
Total
39
7.7
are shown in Attachment 11.
Data specific to road segments required by the WEPP: Road model included road slope, distance
between water diversions, road width, buffer width, insloped or outsloped road characteristic,
presence of ruts, presence of ditch vegetation, fill width, and fill grade. Road slope was
determined using handheld clinometers (Figure 7). Road widths and lengths were determined by
pacing or measuring tape and using a rangefinder, respectively.
The WEPP: Road model also requires the input of the buffer length and slope. These values
generally could not be determined in the field, because the team did not have access to the
private properties adjacent to roads. GIS was used to determine buffer lengths and slopes.
Buffer lengths were estimated by measuring the distance from the road to a well defined channel
9
of concentrated flow. Aerial
photography was used to assist in the
determination of the location of
concentrated flow channels, and in
some cases, decisions of concentrated
flow channel location were based on
best professional judgment. Buffer
slope was estimated using 30 m DEM
in conjunction with the estimated
buffer length.
Soil texture and rock content are also
required inputs necessary to perform
the WEPP: Road model analysis. Soil
types were determined by overlaying
the SSURGO soils layer for the area
Figure 7. Measurement of road slope using clinometer
of interest over the GIS layer of road
segments selected for the model analysis (USDA, 2004). Based on the soil type, the soil texture
and rock content were determined using the County Soils Survey (USDA, 1984). Rock content
is often presented as a range; for purposes of the WEPP modeling analysis, the average rock
content for the given soil type was used.
Climate data used for modeling road segments was based a modified climate file for Eureka
Spring, AR. The WEPP: Road model has built in capacity to modify existing climate files based
on interpolation between data sets from adjacent weather stations. Additional documentation
regarding climate files and the WEPP: Road model can be found at
http://forest.moscowfsl.wsu.edu/fswepp.
Traffic levels were estimated based on location of the road relative to the road network, direct
observation of vehicle traffic, and width of the road segments. To improve modeling
predictions, multiple model runs were performed for the same segment to better reflect estimated
traffic levels. For example, many road segments seemed to have traffic levels that would be
better described as "moderate" rather than the descriptions allowed by the WEPP: Road model of
"low" or "high." To model a road with “moderate” traffic levels, two model runs would be
conducted, one run using "low" and another run using "high" as descriptions of the traffic level.
The results of the two runs were then averaged.
Road surface inputs were determined based on the unpaved road inventory. Similar to the traffic
levels, the road surface could often be better described and modeled using an intermediate
category. The WEPP: Road model interface allows for surface types described as "native,"
"gravel," or "paved." The selection of the road surface description has an effect on the hydraulic
conductivity of the road surface during modeling. Many roads observed during the inventory
appeared to have surface character that was between native and gravel. These road segments
were described as "spot" or having spot coverage of gravel. To model segments that had "spot"
surface types two WEPP: Road model runs, one using "native" one using "gravel" were
10
performed. The results of the two runs were averaged to estimate "spot" road surface modeling
results.
All modeling runs were evaluated using a 30 year simulation period.
Sediment Coefficients and Load Estimates
Using the field survey data and input variables described above, the WEPP:Road model was
applied to each randomly selected road segment to develop an estimate of the sediment
production and annual sediment load entering the Dry Fork Creek stream network. To determine
the sediment production and delivery for randomly selected road segments, each hydraulically
independent sub-segment was modeled. Hydraulically independent sub-segments were
determined based on the detailed field survey of WEPP:Road model input variables. An
illustrated example of hydraulically independent sub-segments is shown in Figure 8. Subsegment #1 includes the portion of a road segment that extended from a crest in the road to the
next point feature in which drainage leaves the road prism through a wing-ditch. Another
hydraulically independent sub-segment (#2) in the same road segment would be from the wingditch in sub-segment #1 to the bottom of the road grade where another wing-ditch is located.
The WEPP: Road model only provides for modeling road segments that are either insloped or
outsloped. To overcome this constraint, road segments were modeled with left and right
components when a road crown was present. In the illustrated example, three model runs would
be required to model the given road segment shown in Figure 8, two sub-segments on the left
side and one on the right side of the illustration.
Figure 8. Illustration of hydraulically independent sub-segments used for WEPP modeling
11
The model results for each hydraulically independent sub-segment were weighted based on the
percentage of the total length of the segment represented by the sub-segment. The sum of the
weighted results represents the total sediment production and delivery for the randomly selected
road segments. Sediment production and delivery results of selected road segments from the
same road groups were then averaged to determine the sediment production and delivery
coefficients for that particular road group. The overall annual sediment load from unpaved roads
for the Dry Fork Creek Watershed was estimated by applying average values to remaining road
segments from the unpaved road inventory. It is assumed that the particle size of the estimated
sediment loads is 0.08 inches or less.
A total of 752 individual WEPP: Road model runs were conducted on 286 individual subsegments to estimate the sediment erosion and delivery coefficients for the randomly selected
road segments. These coefficients were applied to the entire public unpaved road network in the
Dry Fork Creek watershed. The modeling results are shown in Table 4 and represent, for each
road group, estimated sediment erosion coefficients of road surface and road-side ditches, export
coefficients for sediment leaving adjacent buffers, and export coefficients for sediment entering
the stream network. The amount of sediment leaving the buffer and the amount entering the
stream are different due to the presence of farm ponds. These ponds act as settling basins and
reduce the amount of sediment transported to the stream network. It was estimated that 80% of
sediment entering the farm ponds would settle out, based on a review of settling basin sediment
removal efficiency data (Winer, 2000).
Table 4. Results of WEPP: Road modeling analysis of randomly selected road segments
Road Group
(Road Width, Ditch Erosion)
Double Lane
Single Lane, No Ditch
Single Lane, Ditch Erosion > 12"
Single Lane, Ditch Erosion 1-12"
Single Lane, Ditch Erosion < 1"
Average All Roads
Total
Length
Surveyed
(mi)
Count
2
6
10
17
4
1.2
0.4
1.7
4.0
0.5
39
7.7
Erosion
Coefficient
(ton/mi/yr)
Sediment Export
Coefficient
Sediment Export
Coefficient
leaving buffer
(ton/mi/yr)
entering stream
(ton/mi/yr)
25.1
19.5
52.9
41.8
17.7
9.2
14.6
27.7
20.7
4.7
9.2
14.6
27.3
19.4
4.7
37.8
19.6
18.9
The annual sediment load entering the stream network from the erosion of publicly owned,
unpaved roads for the Dry Fork Creek watershed (Figure 2) was estimated to be 1,089 tons
(Table 5). Estimated sediment loads are accurate to ±50% at best (Elliot, 1999). The estimated
sediment loading ratio from public unpaved roads is 20 ton/mi2 for the Dry Fork Creek watershed
(Table 6). Using the estimated average sediment delivery export coefficient for single lane road
designs (Table 4), the sediment load entering the stream network from privately owned unpaved
roads was estimated to be 710 ton/yr. Combining the estimated publicly and privately owned
unpaved roads sediment loads, the total sediment delivery to streams for the Dry Fork Creek
watershed was 1,799 ton/yr. The sediment loading ratio for all unpaved roads in the Dry Fork
Creek watershed was 33 ton/mi2 (Table 6).
Two recent studies have been conducted in Arkansas where sediment loads from unpaved roads
was estimated using the WEPP: Road model. One nearly identical study was conducted in the
North Big Creek (NBC) watershed by the WCRC and TNC in Northeast Arkansas (WCRC,
12
Table 5. Annual sediment loading from unpaved roads in the Dry Fork Creek Watershed
Sediment Export
Coefficient (ton/mi/yr)
Road Group
(Road Width, Ditch Erosion)
Double Lane
Single Lane, No Ditch
Single Lane, Ditch Erosion > 12"
Single Lane, Ditch Erosion 1-12"
Single Lane, Ditch Erosion < 1"
Total Sediment
Load (ton/yr)
Miles
9.2
14.6
27.3
19.4
4.7
3.7
8.2
11.5
30.5
6.7
Public Unpaved Total
Private Roads
34
119
314
590
32
1089
16.5
43
Total
710
1799
2005). The other study was a similar study in which sediment loads from unpaved roads were
evaluated within the West Fork White River (WFWR) watershed in Northwest Arkansas
(ADEQ, 2004). For publicly owned unpaved roads, the sediment production ratio for the Dry
Fork Creek watershed was 20 tons/yr/mi2 compared to 16 ton/yr/mi2 and 29 ton/yr/mi2 for the
NBC and WFWR watersheds, respectively. Reviewing the sediment production ratios for all
unpaved roads in the three watersheds, the WFWR watershed had the highest production ratio at
36 tons/yr/mi2 followed by the Dry Fork Creek Watershed at 33 tons/yr/mi2 and finally the NBC
watershed at 32 tons/yr/mi2. It is of interest to note that although the sediment production ratios
are similar for all three watersheds, the watersheds have differing road densities. This indicates
the importance that watershed specific variables play in estimating sediment loads from unpaved
roads. Sediment loads should not be estimated based on road densities alone. Factors that would
affect differences in sediment production ratios would include variations in topography, climate,
soils, road maintenance activities employed, and overall traffic volumes.
Table 6. Comparison of sediment production and road densities for unpaved road
networks in various watersheds in northern Arkansas
Dry Fork
North Big
West Fork
Creek
Creek
White River
Watershed Area (mi2)
92
54
124
Public Unpaved Roads
Sediment Production Ratio (ton/yr/mi2)
Road Density (mi/mi2)
20.2
1.1
16.4
0.9
29.0
0.8
All Unpaved Roads
Sediment Production Ratio (ton/yr/mi2)
Road Density (mi/mi2)
33.3
1.9
31.8
1.6
36.3
1.0
13
Sediment Reduction Recommendations
Several road segments within the Dry Fork Creek watershed were identified as priority areas for
BMP implementation. The prioritization was based on factors including:
1.
2.
3.
4.
5.
Magnitude of observed erosion
Proximity of road segment to surface water
Location of road segment within the watershed
Local topography
Condition of road surface
Table 7 identifies priority road segments and presents general recommendations for BMP
implementation that will help to reduce sediment delivery to surface waters. Priority road
segments are identified on a watershed map in Attachment 12.
Figure 9. Severe road-side ditch erosion on County Road 2645
Watershed Planning
The information from this study can be used to work with the local counties and other interested
parties to develop a BMP implementation plan that will improve road conditions and reduce
sediment runoff for publicly owned unpaved roads. The county road and city road crews are
excellent resources for identifying additional priority areas and developing effective solutions.
This effort can be part of an overall watershed initiative that also takes into account other sources
of sediment to the Dry Fork Creek watershed.
14
Table 7. Priority road segments in the Dry Fork Creek watershed
Map Identifier
Road Name or
General Description of Local Problem
Number
This road segment is moderately steep and has the potential
to deliver sediment to Dry Fork Creek through direct inputs
via wing-ditches that are located at the bridge. The road
#1
segment winds through a fluvial dissected valley resulting in
CR 1505 – CR3
production of massive amounts of gravels that could be used
Madison – Carroll for road surfacing in other parts of the county. The area of
County Line
significant gravel production may also exacerbate sediment
loading to the stream due to the formation of berms that
prevent water from draining off of the road surface resulting
in increased erosion.
This segment is moderately steep and follows the lowest
elevation along a fluvial dissected valley. This road
configuration does not allow for water to be drained from
#2
the road. The end point of this segment does not provide
CR 541
any opportunity for gravels or fine sediment to settle out of
suspension prior to entering Dry Fork Creek. The road also
generates a large quantity of gravel material that would be
suitable for road surfacing in other portions of the county.
This segment is moderately steep and follows the lowest
elevation along a fluvial dissected valley. The road is able
to drain occasionally; however, there is a significant length
of road that is unable to drain until reaching a culvert
#3
crossing. No settling or sediment filtering is achieved. The
CR 3
road segment results in the generation of gravels that could
White Oak Lane
be removed and utilized for road surfacing in other portions
of the county. There are some opportunities for creating
outsloped conditions resulting in a reduction of concentrated
flow.
The road segment is very steep and is generating a
significant amount of gravel. There are many wing-ditches;
however, due to their proximity to the valley’s steep side
#4
slopes, there is little opportunity for the settling of
CR 518
suspended sediments. There are no cross-drains and a berm
(near intersection
is present, preventing proper road drainage on the east side
with CR 3)
of the segment. Sediment delivery and road maintenance
could be reduced by creating outsloped conditions on the
west side of the road.
The road segment is relatively flat and parallels the north
side of Dry Fork Creek. The road is only able to drain
through a few wing-ditches, and generally the segment
#5
drains directly to the creek with little opportunity for
CR 518
sediment settling. There is a berm that prevents the drainage
Adjacent to Dry
of the road surface. Outsloping this road segment would
Fork Creek
reduce sediment delivery and rutting of the road surface.
There are also a number of springs that drain across this road
segment. The road may be better preserved if culverts were
installed to drain the spring under the road surface.
Suggested BMPs



















Increase distance of
wing-ditches from
bridge
Install cross-drains
Remove and relocate
accumulated gravels
Create outslope
conditions
Install wing ditches
uphill of segment end
point
Install sediment basin
Remove and relocate
accumulated gravel
Possibly, road closure
Install wing ditches
prior to segment
draining to culvert
crossing
Remove and relocate
accumulated gravel
Create outslope
conditions
Install cross-drain
Remove berm on east
side of segment
Remove and relocate
accumulated gravel
Create outslope
conditions
Remove berms
Create outslope
conditions
Install wing-ditches
where appropriate
Install culverts for
spring drainage
15
Map Identifier
Road Name or
Number
#6
CR 550
(South of CR 524)
#7
CR 524
Dripping Springs
Road
Adjacent to Dry
Fork Creek
#8
CR 546
(near Dry Fork
Creek)
#9
CR 518
Dean Road
(West of Highway
21)
#10
CR 524
Dripping Springs
Road
(near spring)
16
General Description of Local Problem
The road segment is moderately steep, climbing out of the
Dry Fork Creek valley. The road parallels an ephemeral
drainage and has the potential to deliver significant amounts
of sediment to Dry Fork Creek. The road is only able to
drain through a few berm breaks that drain directly into to
the creek. There is little or no room for development of
wing-ditches. Creating outsloped road conditions would
reduce sediment delivery to the stream network. Creating
additional breaks in the berms could serve as a possible
alternative until proper outslope conditions are established.
The road segment is very flat and parallels the south bank of
Dry Fork Creek. The road is only able to drain through a
few berm breaks that drain directly into to the creek without
opportunity for the settling of sediment. Plumes of gravel
could be seen in the stream channel where the road drained
to the creek. Outsloping this road segment would reduce
sediment delivery and rutting of the road surface.
There are no drainage structures installed and all sediment
from road and ditch erosion is directly routed to Dry Fork
Creek. Implementation of BMPs on this segment would be
very visible to the public and would serve to increase public
awareness of concerns related to sediment from unpaved
roads.
This road segment is moderately steep and is causing
damage to private lands adjacent to the road segment. The
damage is a result of concentrated flow created by road
drainage that is funneled through breaks in berms located
along the length of this segment. The concentrated flow is
causing significant gulley erosion on the land of the adjacent
property. The segment is generating sediment from both the
erosion of the road surface as well as the gulley that has
been created. As with many of the roads in the watershed,
outsloping the road segment is the most appropriate method
for reducing the generation and delivery of suspended
sediments to the stream network. Also, the gullies could be
arrested using rock check dams, if the property owner is
willing to participate in a BMP implementation
demonstration.
This road segment is moderately flat and follows Dry Fork
Creek near the cave and springs on CR 524. The road is
situated on a bluff much higher than the elevation of the
stream channel, and as a result, has the potential to generate
sediment due to erosion of the hillslope the receives road
drainage. The flow is then concentrated by a berm that
prevents outslope drainage conditions. As much as is
practical, the berm should be removed and outslope
conditions should be established.
Suggested BMPs


Remove berms
Create outslope
conditions


Remove berms
Create outslope
conditions



Install water diversions
Utilize settling basins
Replace bridge


Remove gravel berms
Create outslope
conditions
Install check dams to
arrest gulley erosion



Remove gravel berms
Create outslope
conditions
Map Identifier
Road Name or
Number
#11
CR 526
#12
CR 727
#13
CR 728
#14
CR 728
#15
CR 728
#16
CR 943
(Adjacent to Dry
Fork Creek)
General Description of Local Problem
This road segment is moderately flat and follows a tributary
to Dry Fork Creek. The road segment is near the cave and
springs on CR 524. In this segment, there are few water
draining features, there are several areas where the road
drains directly to the stream channel, and there is a
significant flow from the adjacent state highway that is
intercepted by a ditch. Opportunities exist to reduce
sediment delivery by the development of wing-ditches,
removal of established berms, preventing direct discharge to
the stream channel, and diverting highway runoff to the
stream instead of routing it through the ditch.
This road segment is moderately steep and traverses a
tributary to Dry Fork Creek. The segment has a ditch that is
greater than 12 inches deep, the road drains directly into the
tributary and there are berms present that prevent draining of
the road surface. There is also potential for hillslope erosion
if concentrated flow points are not eliminated. Because of
the proximity of the road to both the tributary and Dry Fork
Creek, there is a high sediment delivery potential for this
segment and action should be taken to reduce the potential.
This road segment is moderately steep and traverses
tributaries that drain to Tan Yard Branch, a major tributary
to Dry Fork Creek. The primary condition that may lead to
significant sediment delivery is direct drainage of road
runoff to the tributaries at culvert crossings. Installation of
wing-ditches located uphill of culvert crossings is
recommended.
This road segment is moderately steep and traverses
tributaries that drain to Tan Yard Branch. The primary
condition that may lead to significant sediment delivery is
direct drainage of road runoff to the tributaries at culvert
crossings. Installation of wing-ditches located uphill of
culvert crossings is recommended.
This road segment is moderately steep and traverses Tan
Yard Branch. The primary condition that may lead to
significant sediment delivery is direct drainage of road
runoff to the tributaries at culvert crossings. Installation of
wing-ditches located uphill of culvert crossings is
recommended.
This road segment is moderately steep and parallels Dry
Fork Creek in southern Carroll County and is one of the
largest contributors of sediment from unpaved roads to Dry
Fork Creek. The road segment has a very high sediment
delivery potential and visual evidence of sediment delivery
to the creek can be seen in the form of sediment plumes.
Primary sources of sediment for this road segment include,
ditch erosion, surface erosion, and hillslope erosion. There
are berms that could be removed to create outslope
conditions. Installation of cross-drains would greatly reduce
ditch erosion and sediment delivery to the creek. At some
point the hillslope on the landward side of the road segment
should be sloped and revegetated.
Suggested BMPs












Install wing-ditches
Remove gravel berms
Create outslope
conditions
Install cross-drains
Install wing-ditches
Remove gravel berms
Create outslope
conditions
Install cross-drains
Install check dams to
reduce ditch erosion
Install wing-ditches
Remove gravel berms

Install wing-ditches
Remove gravel berms


Install wing-ditches
Remove gravel berms


Remove gravel berms
Create outslope
conditions
Install cross-drains
Install check dams to
reduce ditch erosion
Slope and vegetate
adjacent hillslope



17
Map Identifier
Road Name or
Number
#17
Liberty East Road
#18
CR 943
(Newton County)
#19
CR 2360
#20
CR 2645
18
General Description of Local Problem
This road segment is moderately steep and drains to a
tributary of Dry Fork Creek in northern Newton County.
The road segment was identified as a priority segment due to
long stretches of incised road grade that drain to the
tributary.
This road segment is moderately flat and parallels the
western fork of Dry Fork Creek in northwestern Newton
County. The road segment was identified as a priority due
to its proximity to the stream. There are berms preventing
proper road drainage and exacerbating hillslope erosion.
Ditches in the area of this segment were occasionally greater
than 12 inches in depth and installation of cross-drains
would likely reduce ditch erosion. There was also a culvert
in this road segment that was completely blocked, causing
degradation of the road grade. The culvert should be
replaced to prevent damage to the road grade and to reduce
sediment inputs to the stream network.
This road segment is moderately steep and drains to Sites
Branch, a major tributary to Dry Fork Creek. The road
segment drains directly to the tributary via a ditch at the low
point. There is significant ditch erosion. Wing-ditch and
cross-drain installation, where feasible, is recommended to
reduce sediment production and delivery. There is a
potential opportunity to install a sediment basin to trap
sediment that is generated even if appropriate BMPs are
implemented, however this may require that an easement be
obtained. At a minimum, the drainage at the low-point of
the road segment should be dispersed to eliminate the
concentrated flow pattern that now exists.
This road segment is very steep and drains to a tributary of
Dry Fork Creek and is one of the largest sources of sediment
from unpaved roads in the watershed. The site is producing
a large sediment load as a result of severe ditch, road
surface, and gulley erosion. Evidence of an excessive
sediment load is visible at the low point of the road segment.
And the ditches have depths that exceed 3 feet. Installation
of check dams, cross-drains, and wing-ditches is
recommended. There may be enough area at the bottom of
the road segment to install a sediment basin. However, until
the sediment load is reduced by the implementation of other
suggested BMPs, the sediment basin volume required by
current conditions would not be practical.
Suggested BMPs

Install wing-ditches


Remove gravel berms
Create outslope
conditions
Install cross-drains
Replace blocked
culvert












Install wing-ditches
Install cross-drains
Install check dams (if
appropriate)
Install sediment basin
(if feasible)
Disperse flow at low
point of segment
Install wing-ditches
Install cross-drains
Installation of check
dams
Vegetation of ditch
Installation of
sediment basin
Literature Cited
Arkansas Department of Environmental Quality (ADEQ), Environmental Preservation Division.
West Fork – White River Watershed – Data Inventory and Nonpoint Source Pollution Assessment.
2004.
Arkansas Forestry Commission (AFC), Arkansas Forestry Best Management Practices for Water
Quality Protection, 2002
Clingenpeel, A., K. Whitsett. Personal Communication. Methods and assistance for performing
watershed roadway inventory and integrating with the WEPP: Road model. 2004.
Elliot, W.J., D. Hall and D. Schelle. WEPP: Road (DRAFT) - Interface for Predicting Forest Road
Runoff, Erosion and Sediment Delivery, Technical Documentation. U.S.D.A. Forest Service. Rocky
Mountain Research Station and San Dimas Technology and Development Center. December, 1999.
The Nature Conservancy, Strawberry River Preserve Web Page,
http://nature.org/wherewework/northamerica/states/arkansas/preserves/art11144.html, 2005
U.S. Department of Agriculture (USDA), Natural Resources Conservation Service, SURGO Soils,
General Information, Sharp County Arkansas, 2004
U.S. Department of Agriculture (USDA), Natural Resources Conservation Service, Soil Survey of
Fulton and Izard Counties, Arkansas, 1984
The Nature Conservancy. (2003). Ozarks Ecoregional Conservation Assessment. Retrieved June,
2005 from http://www.conserveonline.org/
Watershed Conservation Resource Center, Geospatial Inventory and Assessment of Sediment from
Unpaved Roads in the North Big Creek, Chandler Creek, and Lick Branch Watersheds. March 2005
Winer, R., National Pollutant Removal Performance Database for Stormwater Treatment Practices:
2nd Edition. Center for Watershed Protection. Ellicott City, MD, 2000.
19