AN EVALUATION OF EROSION, SEDIMENTATION, AND DISCHARGE FROM THE TELLS CREEK DRAINAGE IN THE EL DORADO NATIONAL FOREST

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AN EVALUATION OF
EROSION, SEDIMENTATION, AND

DISCHARGE FROM

THE TELLS CREEK DRAINAGE

IN THE EL DORADO NATIONAL FOREST





Michael Walsh Conway

B.S., University of California, Davis,
2003





THESIS




Submitted in partial satisfaction of

the requirements for the degree of





MASTER OF SCIENCE



in



GEOLOGY




at


CALIFORNIA STATE UNIVERSITY, SACRAMENTO



SPRING

2012







ii






































© 201
2


Michael Walsh Conway

ALL RIGHTS RESERVED






iii


AN EVALUATION OF
EROSION, SEDIMENTATION, AND

DISCHARGE FROM

THE TELLS CREEK DRAINAGE

IN THE EL DORADO NATIONAL FOREST



A Thesis



by



Michael Walsh Conway



Approved by:


__________________________________, Committee Chair

Kevin Cornwell, Ph
.
D
.


__________________________________, Second Reader

Timothy C. Horner, Ph
.
D
.


____________________________

Date








iv










Student:
Michael Walsh Conway



I certify that this
student has met the requirements for format contained in the University
format manual, and that this thesis is suitable for shelving in the Library and credit is to
be awarded for the thesis.





__________________________, Graduate Coordinator

___________
________

Timothy C. Horner, Ph
.
D
.





Date

Department of Geology






v

Abstract


of


AN EVALUATION OF
EROSION, SEDIMENTATION, AND

DISCHARGE FROM

THE TELLS CREEK DRAINAGE

IN THE EL DORADO NATIONAL FOREST


by


Michael Walsh Conway


Restoring mountain meadows
within the Sierra Nevada may result in reduced
sedimentation rates and benefits to ecological systems with
in the

watershed and
downstream.
Healthy mountain meadow
s

are believed to attenuate peak runoff rates and
accommodate sediment deposition.
Stream and
sediment discharge data
were

collected

during the 2011 water year

from two
basins drained by Tells Creek

to assess whether the
basins could be distinguished
from one another
based on the
ir

proportions

of

meadow
area

and sediment yield
.

S
tream discharge and

sediment yield data w
ere

compa
red with
results produced by a

geospatial interface for the Water Erosion P
rediction Project
(WEPP) model called
GeoWEPP. Land cover, soil type, and top
ographic geospatial data
inputs

were used within GeoWEPP to model aver
age

annual sediment yield for a five
-
year model period
.




vi

This study provides a hydrologic characterization of the previously unstudied
Tells Creek drainage basin in the El Dorado National Forest, California.
An automated
suspe
nded sediment sampler collected

su
spended sediment samples
daily
during the
spring

of 2011 and again in October, 2011.
The model simulation
constructed in

this
study test
s

the a
bility of the WEPP model to simulate hydraulic processes in a large
2,319
-
hectare catchment

using both field
-
coll
ected
and publically available geospatial
data.

Average annual sedimentation rates for the Tells Creek drainage were likely
under
-
represented by field
-
gathered sediment samples and over
-
predicted by the modeled
sediment yields. Model results
also
support t
he concept that
the Tells Creek

drainage
basin with a greater proportion of meadow area may produce lower rates of sediment
yield.



_______________________, Committee Chair

Kevin

C.

Cornwell, Ph
.
D
.



_______________________

Date




vii

ACKNOWLEDGMENTS


Thank you Dr. Kevin Cornwell. I greatly appreciate your guidance in
constructing

this work.

To my
parents John and Nancy Conway

whose contributions t
o my education are
immeasurable
. Thanks

too

for
keeping me well fed and for providing field and
moral
suppo
rt.

Thank you Tom Eckhardt and fami
ly. I never imagined this project

was possible
until I saw the two
snowmobiles

strapped
on to the

trailer. I am forever indebted to
you
for your

help
.

Thank you
Abdel
-
Karim Abulaban
, for insisting that a concept in its s
implest
terms c
arries the most

weight
.
Thanks
too
for your invaluable guidance
about

how
sediment
moves and insight on
many

other

subjects
.

To my
still
adoring girlfriend, thank you for giving me the time I needed to do
this the hard way
. If we can
continue to support each other the way we have

through
these unfavorable circumstances, we are ready
.














viii

TABLE OF CONTENTS

Page

Acknowledgements

................................
................................
................................
...........

vii

List of Tables

................................
................................
................................
.....................

x
i

List of Figures

................................
................................
................................
...................

xii

Chapter

1.
INTRODUCTION

................................
................................
................................
..........

1

1.1 Ob
jectives

................................
................................
................................
......
1

1.2 Background

................................
................................
................................
...
1

1.3 Previous W
ork

................................
................................
...............................
4

1.4 Project’s Approach to Problem

................................
................................
.....
6

2.
SETTING

................................
................................
................................
......................

11

2.1 Sierra Nevada Geomorphic Province

................................
..........................
11

2.2 Landscape Evolution: Glaciation

................................
................................
15

2.3 Local Geologic Setting

................................
................................
................
15

2.4 Watershed

................................
................................
................................
....
16

2.5 Soils

................................
................................
................................
.............
16

2.6 Land Uses and Cover

................................
................................
..................
19

2.7
Weather

................................
................................
................................
.......
21

2.8 Reconnaissance and Field Visits

................................
................................
.
26

3.
METHODS

................................
................................
................................
...................

27




ix

3.1 Stream Gaging

................................
................................
.............................
27

3.2 Sedime
nt Sampling

................................
................................
......................
38

3.3 Lab Analyses of Sediment

................................
................................
...........
44

3.4 WEPP Model

................................
................................
...............................
44

3.5 GeoWEPP Mo
del Application

................................
................................
....
56

4.
RESULTS

................................
................................
................................
.....................

77

4.1 Stream Gaging Station 1

................................
................................
..............
77

4.2 Stream Gaging Station 2

................................
................................
............
100

4.3 Stream Discharge Modeling

................................
................................
......
109

4.4 Sediment Discharge Sampling

................................
................................
..
111

4.5 Sediment Discharge Modeling

................................
................................
..
123

5.
DISCUSSION

................................
................................
................................
.............

131

5.1 Basin 1 vs. Basin 2, Discharge Comparison

................................
.............
131

5.2 Basin 1 vs. Basin 2, Sediment Yield Comparison

................................
.....
136

5.3 Basin 1 Sediment Yield, First Flush

................................
..........................
143

5.4 Potential Error in Sampling

................................
................................
.......
144

6.
CONCLUSIONS
................................
................................
................................
.........

151

Appendix

A
.

Tells Creek, Station 1: WY 2011 Discharge Data

................................
..

157

A
ppendix

B
.

Tells Creek, Station 2: WY 2011 Discharge Data

................................
...

162

Appendix

C
.

Tells Creek, Station 1and 2: October 2011 Discharge Data

....................

168

Appendix

D
.

Tells Creek, Station 1 and 2: WY 2011 Sediment Discharge Data

........

173




x

Append
ix

E
.

Tells Creek, Station 1: October

2011 Sediment Discharge Data

............

177

Appendix

F
.

GeoWEPP Offsite Summary, Basin 1

................................
.....................

179

Appendix

G
.

GeoWEPP

Offsite Events Summary, Basin 1

................................
.........

183

Appendix

H
.

GeoWEPP Offsite Summary, Basin 2

................................
.....................

218

Appendix

I
.

GeoWEPP Offsite Events Summary, Basin 2

................................
..........

221

References

................................
................................
................................
.......................

256




xi

LIST OF TABLES

Tables











Page


Table 4
-
1 Depth
-
cross
-
secti
onal area relationships

for Station 1.

................................
....

83

Table 4
-
2 Stream
gage

conducted on 11/14/11 at Tells Creek Station 1.

.........................

86

Table 4
-
3 Float tests for velocity, conducted at Station 1

................................
................

87

Table 4
-
4 Stage
-
discharge relationships developed for Station 1.

................................
....

94

Table 4
-
5
Gage
d and modeled wate
r balance data for Basin 1

................................
........

98

Table 4
-
6 Measurements of stage
-
discharge relation
ships at Tells Creek Station 2

......

104

Table 4
-
7
Gage
d and modeled water balance data for Basin 2

................................
......

107

Table 5
-
1

Comparison of Tells Creek annual

sediment discharge
.

................................

141




xii

LIST OF FIGURES

Figures










Page


Figure 1
-
1 Vicinity map of project site.

................................
................................
..............

8

Figure 1
-
2 Detail of
study drainage network
.

................................
................................
.....

9

Figure 1
-
3 Details of

Tells Creek drainages an
d meadow areas
.

................................
......

10

Figure 2
-
1 Map and explanation of geologic forma
tions in the project vicinity

..............

14

Figure 2
-
2 USDA
-
NRCS soil types within the study basins

................................
............

18

Figure 2
-
3 USGS land
-
use classes in the project vicinity

................................
................

20

Figure 2
-
4 Graph of snow w
ater content and precipitation

................................
..............

23

Figure 2
-
5

Van Vleck Meadow
June 24, 2011.

................................
................................

24

Figure 2
-
6

Van Vleck Meadow

April 3, 2011.

................................
................................
.

25

Figure 3
-
1 Map of Basin 1 and Basi
n 2

................................
................................
............

28

Figure 3
-
2 Pressure tran
sducer installed at

Tells Creek at Station 1

................................

32

Figure 3
-
3 Method used to compute discharge using stream gaging

...............................

33

Figure 3
-
4 Floats
used to measure velocity during high
-
stage discha
rges
.

......................

34

Figure 3
-
5 Dischar
ge from Basin 2
on June 24, 2011.

................................
.....................

36

Figure 3
-
6 Di
scharge from Basin 2
on June 24, 2011.

................................
.....................

37

Figure 3
-
7 ISCO sampler suction line in T
ells Creek
at Station 1.

................................
..

40

Figure 3
-
8 Snow conditions

through June, 2011

................................
..............................

41

Figure 3
-
9 Photo of Station 2 installation location

................................
...........................

42




xiii

Figure 3
-
11 Di
agram of WEPP user inputs

................................
................................
......

46

Figure 3
-
12 Example WEPP interface.

................................
................................
.............

47

Figure 3
-
13 Digital elevation model and channels used for Basi
n 1 simulation
.

.............

59

Figure 3
-
15 Project catchments delineated by TOPAZ within GeoWEPP

......................

61

Figure 3
-
16 USDA
-
NRCS soil types used for Basin 1 simulation

................................
...

64

Figure 3
-
17 USDA
-
NRCS soil t
ypes used for Basin 2 simulation

................................
...

65

Figure 3
-
18 Soilsmap.txt and soilsdb.txt files used to define the project area.

................

66

Figure 3
-
19 Soil modification tool in the WEPP model.

................................
..................

67

Figure 3
-
21 USGS land
-
use classes used for Basin 1 simulation

................................
.....

70

Figure 3
-
22 USGS land
-
use classes used for Basin 2 simulation

................................
.....

71

Figure 3
-
23 Landcov.txt and landusedb.txt files used to define the project area.

............

72

Figure 3
-
24
WEPP/Topaz translator land
-
use associations for Basin 1 and Basin 2

.......

73

Figure 3
-
25 Rock:Clime climate modification interface.

................................
.................

75

Figure 3
-
26 Five
-
year simulate
d precipitation patterns

................................
....................

76

Figure 4
-
1 Water stages in Tells Creek, at Station 1, for the 2011 water year.

................

78

Figure 4
-
2 Stream cross
-
sectional area at Station

1
.

................................
.........................

80

Figure 4
-
3 Stream cross
-
sectional area at Statio
n 1
.

................................
.........................

81

Figure 4
-
5 Stream gage conducted on 11/14/11 at Tells Creek Station 1.

.......................

86

Figure 4
-
6 Unregulated inflow to Union Valley reservoir
during the 1995
.

....................

90

Figure 4
-
7 Discharge versus exceedance probability for South Fork Silver Creek.
.........

91

Figure 4
-
9 Difference
between gaged and rating curve discharges
.

................................
.

96




xiv

Figure 4
-
10 Discharge at Tells Creek at Station 1 for the 2011 water year.

....................

99

Figure 4
-
11 Average daily water stages in Tells Creek, at St
ation 2
.

.............................

103

Figure
4
-
12: Stage
-
discharge relationship at Tells Creek, Station 2.

.............................

105

Figure 4
-
13

Difference between gaged rating curve discharges
.

................................
....

106

Figure 4
-
14 Average daily

discharge at Tells Creek
.

................................
.....................

108

Figure 4
-
16 Daily discharges versus sediment yield at Tells Creek, Station 1.

.............

117

Figure 4
-
17 Daily discharge concentration at Tells Creek, Station 2.

............................

118

Figure 4
-
18 Daily discharges versus sediment yield

at Tells Creek, Station 2.

.............

119

Figure 4
-
19 Hourly discharge at
Tells Creek, Station 1

................................
.................

120

Figure 4
-
20 D
aily
sediment discharge at Station 1,

October 14, 2011

...........................

121

Figure 4
-
21 Daily discharges versu
s sediment, Station 1, October

2011

.......................

122

Figure 4
-
22 GeoWEPP
-
simula
ted average a
nnual soil loss,

Basin 1.

............................

126

Figure 4
-
23 GeoWEPP
-
simulated aver
age annual sediment yields,
Basin 1.

................

127

Figure 4
-
24

WEPP s
imulations
of October
2011

................................
...........................

128

Figure
4
-
25 GeoWEPP
-
simulated average

annual soil loss,
Basin 2.

............................

129

Fi
gure 5
-
1

Comparison of
daily discharge for Tells Creek Basin 1 and Basin 2.

..........

135

F
igure 5
-
2 Comparison of daily sediment discharge, Basin 1

and Basin 2

....................

140

Figure 5
-
3 Measured
daily sediment dischar
ge concentration,

Basin 1 and Basin 2

.....

142

Figure 5
-
4 Illustration of sedim
ent sample concentration error

................................
.....

147

Figure 5
-
5 Streambed sediment samples from Station 1

................................
................

148

Figure 5
-
6 Deviation of sediment sam
ples from true mean concentrati
on
.

....................

149




xv

Figure 5
-
7 Vertical distribution of sediment i
n the water column

................................
..

150

1



Chapter 1

INTRODUCTION

1.1
Objectives

This project evaluates
the potential for a reduction in sediment yield from
two
drainages in the El Dorado Nation
al

Forest
that may result from the restoration of
degraded
meadowlands
.

Stream flow and
suspended sediment discharge were

gage
d at
two locations in the Tells Creek drainage during the 2011 water year
and in October,
2011
in an attempt to distinguish two basins from one another based on their proportion
of meadow area

and sedi
ment yield
.

This study
also

attempts to

further the objectives of
the National Fish and Wildlife Foun
dation as described in the
2010
Sierra Nevada
Mea
dow Restoration Business Plan

(NFWF, 2010) by providing valuable watershed data
concerning

targeted restor
ation areas.

1.2 Background

California Water
Setting

and Regulatory Action

Through a complex network of managed rivers, streams, canals, and reservoirs,
Californians enjoy both a water supply and flood protection. Surface water runoff from
the Sierra Nevad
a Mountains provides an important
source of
drinking water for most of
California

(DWR, 2011
)
. As California’s population
increase
s, the need for more
innovative methods of supplying
clean
water throughout the state grows, as does the need
for protection
of ecologic resources.

Alt
hough California has a long history being able to
2



supply water to its residents at each end of the state, this bountiful resource will likely be
strained

even more
by
competing uses in the future

(DWR, 2011
)
.

The California State
Department of Water Resources describes in its most recent
Water Plan the issues that face the state’s water supply. At a time when the state needs
dependable water supply for its growing population, numerous threats plague the security
of
the state’s

wate
r quality and supply. Natural habitats that historically buffered streams
and wetlands are fewer in number
because

of urbanization, agriculture, industrialization,
recreation, and other land uses. Between 1998 and 2005, changes in groundwater and
surface w
ater storage in California equaled negative 51 million acre
-
feet. Though this is a
snapshot in time in terms of water supply, it describes the demand for water in the state.
Consequently, developing an integrated approach to water management is central to
the
success of California’s water future

(DWR, 2011
)
.


One step taken by regulatory agencies to protect the beneficial uses of the state’s
water is to limit sediment input sources. Effective management of sediment inputs into
the state’s water bodies not o
nly satisfies regulatory requirements but also may provide
substantial health benefits to habitat and other downstream users (USEPA, 1998).


A Conference Report prepared for Interior and Related Agencies in response to
the 1993 Appropriation Act (H.R. 5503
), requested an ecological inventory of National
Forests including those in the Sierra Nevada. The Sierra Nevada Ecosystem Project
(SNEP) was initiated to assess the ecological condition of the Sierra Nevada, including
the El Dor
ado National Forest. A Scie
nce T
eam was responsible for evaluating and
reporting on state of various environmental assets contained in the forest, including water
3



resources. The SNEP contains a vast body of research characterizing past, present, and
future impacts to watersheds in t
he El Dorado National Forest. The SNEP
describes
current

threats to watersheds in
the

El Dorado National Forest
, including sediment
delivery

and

also support
s
joint management strategies aimed a
t

protecting Sierran
resources (Millar, 1996).

Degraded Areas
Contribute Excess Sediment


Mining
and forestry generated
debris dominated sediment yields from the Sierra
Nevada to the Central Valley during most of the 19
th

and 20
th

centuries.
Significant
disturbance within stream corridors often resulted in increase
sedimentation rates
(Kattelmann, 1996).


Along with 20
th

century advances in analytical methods,
has come
the
understandin
g of how toxic compounds bind

to sediment

(Idaho DEQ, 2003)
.
For this
reason
the
United States
Environmental Protection Agency (
US
EPA)

cites sedimentation
as a critical problem in many geographic re
gions within California and throughout the
United States (
US
EPA, 1998
)
.

Restored Meadow Benefits


Meadows possess great potential for attenuation of peak
storm
flows and

their
corresponding sediment
discharges

(
Federal Interagency Stream Restoration Working
Group, 1998)
.
The benefits of mounta
in
-
meadow stream restoration
may
include
decreased downstream sediment loading

in discharge waters

and increased sediment
storage capacity

within the meadow itself
. High
-
Sierran drainages
have the potential
to
remove
a
hi
gh volume

of sediment
at its source, therefore d
rainages containing a greater
4



proportion of healthy mountain meadows are more likely to store sediment and reduce
downstream
sediment loads

(NFWF, 2010)
.

1.3 Previous Work

Problem Areas Identified


A recent National Fish and Wildlife Foundation business plan describes the need
to restore and conserve Sierra Nevada mountain meadows (NFWF, 2010). The “Sierra
Nevada Meadow Restorat
ion


Business Plan


contemplates a range of adverse
environmental impacts resulting from meadow degradation, including loss of habitat and
reduced

water storage capacity. E
cological studies such a
s

Spencer

and Ksander
, 2002,
detail
specific adverse
affect
s

resulting from sedimentation
.
F
ields
including
ecology,
geology, and hydrology
currently provide

insight to meadow processes and
tools for
how
to restore

meadow ecosystems with improved hydrologic function

(H
ammersmark et al
.
,

2008).


United States
Forest Service (USFS) conducted many studies of sediment
production and watershed health in conjunction with the SNEP, including “Camp and
Clear Creek, El Dorado County: Predicted Sediment Production from Forest
Management and

Residential Development
(
McGu
rk et al.
, 1996).


This study of the
Cosumnes River basin provides valuable information about the causes and rates of
sediment p
roduction along the western slope

of the Sierra Nevada

and
near

this project
.
This

SNEP study was conducted in the hydrologic su
b
-
a
rea immediately south of the
American River basin
, the basin
that

is the subject of this project

(OWP, 2011
).

5




The El Dorado National Forest began implementing the Travel Management Plan
in January 2009. T
he P
lan identifies current forest management str
ategies and their
associated i
mpacts on the environment. The P
lan describes environmental threats to
forest areas and delineates the areal extent of impacts

(USDA, 2008)
. The Plan describes
how unauthorized motor vehicle access is a major threat to forest
ecosystems and results
in exces
sive sediment production. This P
lan also provides great insight to reasonably
foreseeable impact
s and solutions for the forest, which include reducing sedimentation
and meadow restoration

(USDA, 2008)
.

Restored Meadow
Demons
tration
s


Multiple watershed improvement groups in California seek to demonstrate
benefits brought by mountain meadow restoration, including mitigation for peak flows
and flood reduction, mitigation for
the influence of climate change

on water supply, and
mitigation for reduced biological habitat created by logging, urbanization, and other
hydromodification

practices (American Rivers, 2011
). The Feather River Coordinated
Research Management (FRCRM) group is active in demonstrating new methods for
meadow res
toration. The group is also
a
value
d

source of information
on
previous
meado
w restoration projects. In 1994

the group engaged in a meadow restoration
project
in Plumas National Forest and successfully demonstrated a 17.5 percent reduction annual
sediment
producti
on (American Rivers, 2011; FRCRM, 2011
).

Model Applications


The United States Department of Agriculture (
USDA
)

Forest Service Rocky
Mountain Research Station

(RMRS)

is actively engaged in applying watershed
-
scale
6



erosion and sediment yield models
to forested watersheds
with the help of the Water
Erosion Prediction Project (WEPP) model

(Flanagan and Nearing, 1995)

and a geospatial
tool for ArcGIS, called GeoWEPP

(Renschler, 2001)
. The work of the RM
R
S has helped
improve

the WEPP and GeoWEPP models f
or forest applications. Their work
also
indicates that the inherent ability of WEPP and GeoWEPP to build in specific vegetative
management and soil controls gives it an advantage over finite difference and finite
element models in forest applications

(
Dun

et al.
, 2009)
.

The WEPP model has gained
favor over the Universal Soil Loss Equation
(USLE)
for watershed applications due to its
tight control over surface and subsurface water movement and erosion processes.
The
GeoWEPP model
demonstrated
accurate
simula
tions of
runoff in forested watersheds
(Dun et. al., 2009)
and

accurately predict
ed

erosion and sediment yield in
a
r
elatively
large
-
scale
,
490
-
hectare

watershed

in Turkey

(
Yüksel

et al.
, 2008)
.

1.4 Project’s Approach to Problem


Sediment discharge w
as
monitored at two locations
, Station 1 and 2,

along

Tells
Creek, in the El Dorado National Forest, during both the spring runof
f period between
April and June, 2011
an
d at the initiation of the rainy season
in
October
, 2011

(Figure 1
-
1
and 1
-
2)
. The first
m
onitoring
period typically encompasses the most significant runoff
period in terms of volume, while the second period attempts to capture the first rain event
of the season that may convey sediment disturbed during the busy summer camping and
recreation se
ason.


The two

monitoring locations
chosen
in the Tells Creek drainage provide data
from two drainage units with significantly different proportions of meadow area.
The two
7



drainages were evaluated to determine if the difference in meadow area is related t
o a
difference in suspended sediment discharge.
The hypothesis proposed by this study is that
a basin with a great proportion of healthy mountain meadows is more likely to trap
sediment.
Figure 1
-
3 shows the two drainages m
onitored for this study and
meado
w areas

identified by the USDA

(USDA, 2005)
.


GeoWEPP

was used to model
average annual
s
ediment loss and yield for the
project
site
.
Using Geographic Information System (GIS) datasets such as soil

type, land
use, and topography

allowed for a quantitative a
ssessment of potential benefits resulting
from meadow restoration.
The model provided

an additional tool for estimating
watershed discharge and sediment
yield,

which is especially helpful given the difficulty
in gathering representative data in the field during high flows and high snowpack
conditions.


8




Figure 1
-
1
:

Vicinity map of project site.


Station 2

Station 1

9






Figure
1
-
2:

Detail of drainage network with Tells Creek and Union Valley Reservoir for
reference.



Station 2

Station 1

10




Figure 1
-
3: Details of two Tells Creek drainages and meadow areas identified within.

Basin 1
and Station 1
is on the left,

Basin 2
and Station 2
is on t
he right,
and
meadows
are in orange (USDA, 2005).










Station 1

Station 2

11



Chapter 2

SETTING

2.1
Sierra Nevada Geomorphic Province


The Sierra Nevada Geomorphic Province extends approximately 700 km in
length
along the eastern edge of California, between the Mojave Desert in the south and the
Modoc Plateau in the north. The mountain range is roughly 100 km wide and is situated
between Lake Tahoe on the California
-
Nevada border

on the east

and the Central

Valley
to the west. Along its
crest,

it contains peaks ranging from 2
-
4 km

above sea level
. This
region
,

combined with the Central Valley, form the rigid Sierran

microplate bound to the
east by the Eastern California shear zone and to the west by the San
Andreas
Fault

system
(Cecil

et al
, 2006).


The size and shape of the Sierra Nevada range is
largely attributed

to pre
-
Cenozoic events, but smaller scale drainage features may have
developed

during the
westward tilting of the range (Cecil

et al.
, 2006). Tw
o phases of orogenic activity en
ding
at 85 Ma (Wakabayashi, 2000
) resulted in a granitic Mesozoic batholith that forms the
basement in the American River hydrologic unit (James, 1995). This arc magmatism
created plutons of monzonite, granodiorite, and gran
ite throughout the Sierras in regions
underlain by the batholith. Middle to Lower Jurassic marine formations,
Pleistocene

volcanic basalts, and Quaternary alluvium and glacial deposits
are

observed in the studied
area
(Jennings et. al, 2010).
Very few indi
cations of metamorphism appear in the st
udied
area, but clear evidence

of the mid
-
La
te Jurassic, Nevadan orogeny
is located

12



approximately 50 km to the west (Hacker, 1993).
Figure
2
-
1

shows the geologic
formations in the project area

(Jennings et. al, 2010).


Subduction
-
driven volcanism occurring in the Cenozoic between 35 and 5 Ma
covered many of the Sierran drainages, though it is unclear how extensive its impact was
in the American River hydrologic unit. Calc
-
alkaline andesitic volcanism in the central
and

northern Sierra Nevada occurred in pulse
s primarily between 15
-
6 Ma, which
provide
s

evidence for multiple tectonic scale events in the region. Deep central Sierran

paleocanyons record the tilt history of the range and possibly significant tectonic events
such as the beginning of arc magmatism, initiation of Basin and Range extension, and
even the passage of the Mendocino Triple Junction. Collapsed lava domes created
volcanic ash and debris flow structures recorded a succession of tilted strata and
paleogra
dients.
Alt
hough volcanic deposits are much more prevalent to the north and
south of the studied area,
there is good evidence that

drainages

within the study area were
at least partially

carved by volcanic activity (Busby et al., 2008).
Unfortunately,

a limited
depositional record of
volcanic
s

is observed in the studied area.

Early Cretaceous uplift of the Sierras was followed by significant erosion and
stream incision of the Sierra Nevada range, which occurred most notably during at least
two upl
ift events within
the last 5 Ma (Wakabayashi, 2000
). Following a decrease in
volcanism, rapid uplift rates recorded in this period indicates that in response to
lithospheric removal beneath the range, a buoyant response resulted in more than 1 km of
range
uplift at the crest (James, 1995). The tilting of the range is thought to be a more
significant driving force
in incising Sierran streams
than climatic factors (Jones et al.,
13



2004). Uplift of the range resulted in westward tilting and westward flow pattern
s along
with significant stream incision in rivers and drainages within this province. Extensive
Quaternary glacial deposits and decomposed basement rocks indicate that glacial
processes were significant in the region.





14




Era

Symbol

Description

Quaternary

Qg

Glacial till and moraines. Found at high elevations
mostly in the Sierra Nevada and Klamath Mountains.



Qv

Quaternary volcanic flow rocks; minor pyroclastic
deposits.

Mesozoic

J

Shale, sandstone, minor conglomerate,
chert, slate,
limestone; minor pyroclastic rocks.



gr
Mz

Mesozoic granite, quartz monzonite, granodiorite,
and quartz diorite.

Paleozoic

Pz

Undivided Paleozoic metasedimentary rocks. Includes
slate,
sandstone
, shale, chert, conglomerate,
limestone,
dolomite, marble, phyllite, schist, hornfels,
and quartzite.


Figure
2
-
1
: Map
and explanation
of geologic formations in the project vicinity

(Jennings
et. al, 2010).

Study basin

15



2.2

Landscape Evolution: Glaciation


Pleistocene glaciation was likely a significant source of sediment for the South
Fork American River hydrologic area as well as the sub
-
basins and perhaps the mountain
meadows within (Brocklehurst, 2002). Glacial erosion may also be associated with
lithosp
heric uplift of the Sierras in the late Cenozoic (Jones et al., 2004). The first in the
series of three significant Wisconsin period glacial advances in the region was the Tahoe
advance
. The Tahoe advance began sometime between 80,000 and 60,000
years ago
.

The
Tenya glacial advance occurred following the Tahoe, but little is
known

about its exact
age. The next significant and datable advance in the region was the Tioga. The Tioga
advance is differentiated into four stages defined by moraines, with ages betw
een 3
1,000
and 16,000
years ago

(James,
2002). The region experienced significant glacial events
as
early as

2.5 Ma and
as recent as

2

Ka. More
recently,

the Little Ice
Age
could have
influenced

channels in the region as recently as 200 years ago (Clark, 2007). It is
important to mention however that regional scale incision of northern Sierra drainages in
the late Cenozoic may be in response to uplift and decreased volcanism and that
Quaternary g
laciations could be a less significant
erosion
al

force (James, 1995).
G
lacial
till

deposits

were
also
identified

in
the Van Vleck meadow

during field visits between
June and August 2010
, conducted as part of this study
.

2.3

Local
Geo
logic Setting


The Sier
ra Nevada acts as a barrier for
moisture
-
laden

clouds and captures a
significant portion of rain bearing weather systems moving inland from the
Pacific
Ocean. Rain and snow forced to fall in the region

supports much of California’s
16



population. Regionally
,
the

study area is located 32 km northeast of Placerville and 24
km north of the South Fork of the American River within the El Dorado National Forest.
The boundary of the studied drainage
area

is approximately 6 km south of Loon Lake and
3 km northeast of
Union Valley Reservoir. The Crystal Range immediately east of the
studied drainage trends northwest
-
southeast and is a drainage divide conveying water
west and southwest towards the South Fork of the American River. The study area
contains both meadows and

mountain ridges and var
ies in elevation between 1,800

and
2,200 m
eters

above mean sea level (amsl
)

(
Jennings et. al, 2010)
.

2.4

Watershed


The American River hydrologic sub
-
area contains the North, Middle, and South
forks of the American River
and

the Upper Bear River. The South Fork American
hydrologic sub area contains Tells Creek drainage
,

which includes
first through fifth

order streams that drain towards Union Valley Reservoir. Of the 4820 km
2

drained by the
American River watershed,
the
South

Fork sub
-
shed
encompasses
804 km
2
. The South
Fork of the American River contains a mixed bedload and flows across both coarse
alluvial and

bedrock dominated sections of the drainage (
Valle and Pasternack,

2002)
.
Figure 1
-
1 shows the extent

of the studied
drainage basin and Figure 1
-
2 shows a detail of
Tells Creek.

2.5

Soils


Soils in the study area are generally thin and underlain by bedrock. Low lying
meadows are filled with alluvium from decomposed local sources. Soils in the region are
17



generally weakly
cemented and range between cobbly
,

sandy
,

loam to silt loam. Rock
outcrops are observed between depths of zero to three meters depth beneath the soil
surface. Though soils of variable hydrologic capacity are observed in the area, infiltration
capacity is g
enerally moderate to high and runoff coefficients are gener
ally moderate to
low (USDA, 2011
).

Figure 2
-
2 shows
the distribution of
soils in the project vicinity.



18





Figure 2
-
2
: USDA
-
NRCS soil types
within the study basins

(USDA, 2011
).




19



2.6 Land Uses

and Cover


United States Department of Agriculture (USDA) Forest Service maintains and
administers use in most of the study area, though some areas are also designated non
-
National Forest System Lands. Recreation and wildlife habitat uses currently domina
te
modern land uses

in

the area, though historic uses for the area include grazing and timber
harvest.
The soils and general geography of the area make the land suitable for grazing
and recreational use, but has little value for crop cultivation (USDA, 200
9).


Currently the Forest Service has a renewed interest in addressing the
environmental impacts

of

unmanaged Off
-
Highway Vehicle (OHV) traffic. The Forest
Service adopted new laws governing OHV traffic in January 2009, in hopes of continuing
to provide ad
equate recreational opportunities for its visitors as well as managing erosion
and se
dimentation rates and protecting

downstream beneficial uses. Union Valley
Reservoir
, immediately downstream of the project site,

produces hydroelectric power for
the City
of Sacramento. The

studied watersheds and immediate
vicinity

are identified by
the Forest Service

as an area with valuable water resources

(USDA, 2008
).


The United States Geological Survey (USGS) maintains a database of land cover
typ
es in the United Stat
es

developed using remote sensing techniques

(Homer

et al.
,
2004)
. These classifications are general but useful in this study as an input for the
GeoWEPP model. The information contained in this graphical database indicates that the
study area conta
ins pri
marily evergreen forest and some other land uses subject to
interpretation.

Figure 2
-
3 shows land cover types in the project vicinity.

20




Figure
2
-
3
: USGS land
-
use classes
in the project vicinity

(Homer et. al, 2004).




21



2.7 Weather


The project area
receives approximately 1,6
68 millimeters

of precipitation
annually,

most of which falls as snow (OW
P, 2011). Mean daily high temperatures range
between about 24°
C (75°F) in July and about 6°C (42°F) in December, while mean daily
lows range between about 7°
C (45°F) in July and about
-
9°C (15°F) in December (DWR,
2011).


The closest weather study area is located near Van Vleck meadow and owned by
Sacramento Municipal Utilities District (SMUD). Data from this station is archived at
DWR’s California Data Exchan
ge Center (CDEC), filed under station identifier “VVL.”
The snow water content data record begins in 1972 and is still active. The precipitation
record begins in 1995
, but contains no data for the 2011 water year. The precipitation
data for the 2010 water
year is also incomplete.
Unfortunately no other nearby weather
stations were identified.

A precipitation record for the last two years was estimated for this study based on
the relationship between snow water content and precipitation during the 2009 wate
r
year. Because most precipitation in this area falls as snow, it
was

assumed that the
precipitation record typically matches the snow water content record. The relationships
between snow water content and precipitation for water years 2009 throu
gh 2011 ar
e
shown in Figure 2
-
4
. The 2009 water is approximately a typical water year for this
location. In 2011, the project site received approximately 200% of normal precipitation
22



(
DWR
, 2011).

Figure 2
-
5 and 2
-
6 show unusually high snow levels at the Van Vleck
Me
adow and at its
ultimate
discharge culvert.



23






Figure
2
-
4
: Graph of snow water content and precipitation for water years 2009 through
2011

from the Van Vleck weather station located at an elevation of 2,042 meters
amsl
(DWR ID: VVL).
(*)
Precipitation was estimated for water years 2010 and 2011 based on
snow water content data (DWR, 2011).





0
500
1000
1500
2000
2500
3000
3500
0
200
400
600
800
1000
1200
1400
1600
1800
2000
10
11
12
12
01
03
03
04
05
06
07
08
09
Accumulated Precipitation (mm)

Snow Water Content (mm)

Monthly Snow Water Content and Cumulative Precipitation

Water Years 2009
-
2011

WY 2011 Snow Water
WY 2010 Snow Water
WY 2009 Snow Water
WY 2011 Precip*
WY 2010 Precip*
WY 2009 Precip
Month

24






















Figure 2
-
5: Van Vleck Meadow, from its southwestern edge, looking east on June 24
,
2011
.




25























Figure 2
-
6: Van

Vleck Meadow discharge culvert, near Station 2
. Photo taken April 3,
2011.




26



2
.8

Reconnaissance

and
Field Visits


Field

conditions were evaluated

multiple times
in the project area between June
and September 2010
. Some
of the
study area

is

accessible by forest service access roads
and some by hiking trails. Most reaches of Tells Creek are in
accessible by road or trail
during most of the dry season
due to

thick vegetation.
Though much of the vegetative
growth

thins around Tells Creek during
the winter, p
lants
grow

quickly in and adjacent to
the creek

following the seasonal
snowmelt
. Tells Creek contains significant lengths of
bedrock
-
controlled

channel. No appropriate areas were ident
ified to perform pebble
counts because there was very littl
e loose rock in the channel and no significant bars of
rock.


Both Basins 1 and 2 contain substantial portions of formerly heavy logging areas.
These identified areas are substantially recovered throughout the study area. No excessive
erosion was observed
in these areas.


Motorized vehicle accesses cross Tells Creek at multiple locations. In some cases
it was apparent that
Forest Service staff created obstructions in the road to prevent
motorized vehicle crossing. This is presumed to reduce the impacts of
sedimentation
produced by motorized crossing of Tells Creek. This action may not necessarily point to
a specific problem area, but may instead reflect Forest Service management protocols
that seek to reduce sedimentation impacts from roads throughout the E
l Dorado National
Forest (
USDA, 2008
).



27



Chapter 3

METHODS


As much as 80% of total precipitation in the South Fork
American River
hydrologic area is discharged between J
anuary and June each year (
Valle and Pasternack
,
2002).

This project attempted to capture data from as much of
the
sp
ring runoff season as
possible, with the objective of also capturing the most significant period of sediment

discharge. Stream

and sediment discharge data were

also collected during the first ma
jor
runoff event of the 2012 water year. This second deployment of sampling equipment was
an attempt to capture sediment discharges that may be related to land disturbance during
the busy summer recreational season. The production of finer sediments due

th
e
pulverizing action encountered on dirt roadways

is believed to be a
significant source of
soil loss in the

El Dorado National Forest (USDA
, 2008).

3.1

Stream
Gaging


Each sampling station required a unique method for computation of discharge,
due to diff
erences in accessibility, flow volume, and velocity.

Station
1
(Latitude: 38.903;
Longitude:
-
120.368)
captured a much larger
drainage, which required stream
gaging

techniques for discharge determination.

Station 2

(Latitude: 38.932; Longitude:
-
120.319)
ca
ptured a small enough drainage area to utilize a V
-
notch
weir and
pressure transducer
system. Figure 3
-
1 shows drainage Basins 1 and 2 an
d their associated discharge

monitoring points, Station
s

1 and 2, respectively.


28




Fi
gure 3
-
1
:
Map of Basin 1 and Basin 2 and their associated outlet points, Station 1 and
Station 2
,

respectively. For the purposes of this study, Basin 1 includes all of the Basin 2
area as well. Tells Creek flows through the middle of each basin and is defined by the

dark blue line. Basin delineation was performed in TOPAZ (Garbrecht and Martz, 1997).




Basin 1

Basin 2

29



Station 1


At Station
1

discharge was determined using
the

rat
ing curve

developed for this
study
,
which was
produced through
four measured

stream
gaging

events

and

re
ported
disch
arges (USGS, 1971
;
Devine Tarbell & Associates, Inc., 2005
)
.

Discharge calculated
dur
ing the
gaging

events was

correlate
d

with pressure transducer
stage
data collected at
the same
location.

A

non
-
vented
Solinst pressure transducer was secured
inside a PVC
pipe and was bolted directly

to the bottom of Tells Creek.
Water levels were recorded
every hour. These creek s
tage values

were later corrected to

account for changes in
atmospheric pressure
, using a barometric pressure logger m
ounted in the V
an Vleck
meadow.
These stage measurements were used to calculate discharge using the rating
curve.
Figure
3
-
2 shows how the pressure

transducer was mounted to the bo
ttom of Tells
Creek at Station
1
, with
in
five

meters

of where stream
gaging

was conducted.


Using stream
gaging

methodologies described in Rantz, 1982, four surveys of
stream discha
rge were conducted at Station 1
, one using traditional
gaging

techniques
and a velocity meter and the other using floats
.
The first stream
gaging

session was
conducte
d using traditional stream
gaging

techniques. Velocity data was collected

using

a
Marsh
-
McBirney

FLO
-
MATE veloc
ity meter mounted to a 1.5 meter

stream
gaging

staff
.
These readings were used

to deter
mine discharge at parallel water columns

within the
channel cross
-
section. Velocity readings were gathered from a depth equal to 60% of
total depth below the water surface
(Rantz, 1982
).
Velocity

readings were averaged over
a

period of one minute

for each vertical column of the creek.

Nineteen d
iscrete columns

were used to define the cha
nnel cross
-
section at Station 1
, each one
foot apart. A

cross
-
30



channel distance was marked with a tree mounted horizontal (+/
-

1 degree) steel
gaging

line with
brass markers at

two
-
foot intervals. Figure 3
-
3 graphi
cally
shows

the

standard
stream
gaging

and discharge calculation methodology that was used

for this study
.


The three float tests were performed on April 2, April 7, and July 10, 2011
; floats
provided a useful means of estimating velocity when high discha
rge stages made in
-
stream velocity measurements unsafe
.
In

thes
e tests for velocity,
11 to
15 oranges

were

used per
gaging

session. The oranges

were

individually

placed in Tells Creek and
tracked
across a
marked 12
meter

section o
f the creek
; travel time

w
as recorded. O
ranges are
considered neutral
-
density relative to water and
appropriate for float tests (Rantz, 1982).
Neutral
-
density floats are not subject to
significant
wind resistance encountered at the
water surface because they
f
loat

just below the surface. Their travel time and resulting
velocity

however

is
usually
higher than the assumed average velocity
for the vertical
cross
-
section of the stream
segment
being measured.
The vertical distribution of stream
velocity within each cros
s
-
sectional segment
varies with

channel shape
, bed co
nditions,
and flow rate. The relationship between float velocity and average velocity in the vertical
segment is also dependent on the float depth beneath the surface.

A common factor used
to get the ass
umed average velocity in the vertical segment a
long the float length, is 0.85
(Costa et al., 2000; Rantz, 1982).
This factor was used
in this study
to c
ompute
average
float
velocities
.

Figure 3
-
4

shows a group of oranges used in a float test.


The equation
s listed below were used to compute discharge (Q), as described
in
Rantz, 1982.
Equation (
3.
1) explains how each successive piece of the cross
-
sectional
area is measured from a base point. The average velocity of each piece is used to
31



calculate a represent
ative discharge for that piece (q).

Equation (3.2
) states that the sum
of the area and velocity of each vertical section of stream
gage
d is equal to the discharge
of the entire stream.


q
x

= v
x

* (
(
b
x



b
x
-
1
)

/ 2

+
(b
x+1



b
x
) / 2
) d
x


(3.1)


Q =


(a * v)






(3.2)


Where


q
x

= discharge through subsection x


v
x

= mean velocity at vertical x


b
x

= distance from initial point to vertical x


b
x
-
1

= distance from initial point to preceding vertical


b
x+1

= distance from initial point to next vertical


d
x

=
depth of water at vertical x



Using pressure transducer measurements and results from the four stream
gaging

events, a discharge rating curve was produced.
Further discussion of the development
of
the rating curve is included

in Chapter
4
.


32




Figure 3
-
2
:
Pressure transducer installed inside of a PVC pipe, bolted to bo
ttom of Tells
Creek at Station
1
. Water level measurements were recorded between November 5, 2010
and October 14, 2011.

33





Figure 3
-
3
:
M
ethod used to compute discharge using stream
gaging

(Rantz, 1982)
. This
method was utilized to compute discharge at Station 1on November 5, 2010.







34





Figure 3
-
4
: Floats were used to measure velocity
during high
-
stage discharges. Rantz,
1982 describes the methodology for using floats to
gage

stream vel
ocity
.





35



Station 2


At Station
2
, discharge was calculated from pressure transducer data collected
behind a V
-
notch weir secured to a 36
-
inch culvert
, just below Van Vleck meadow
. A
Solinst pressure transducer was installed behind a V
-
notch weir at the
drainage culvert
for the Van Vleck Meadow
,

in the summer
o
f
2009

(Mancuso, 2011
)
. The transducer was
programmed to collect head data

every 15
minutes
, throughout the

study period

of this
project
.

Using
equation
(
3.
3
) described in Fetter (1994)

discharge (Q) was determined,
where H

(pressure transducer data)

is equal to head
in
meters
.


Q = 1.38
H
5/2






(
3.
3
)



Figures 3
-
5 shows the discharge culvert for the Van Vleck meadow where water
levels were recorded. Figure 3
-
6 show
s

an

example of how
much water bypasses the
culvert by flowing over the roadway and around the culvert. Estimates of bypass water
were completed in the 2
010 water year by (Mancuso, 2011
) and used in the development
of the stage
-
discharge relationship for Station 2.

36























Figure 3
-
5: Discharge from Basin 2 at the lower Van Vleck meadow culvert on June 24
,
2011
.



37
























Figure 3
-
6: Discharge from Basin 2 at the lower Van Vleck meadow tops roadway on
June 24, 2011.


38




3.2

Sediment Sampling


Sta
ble
stream cross
-
sections were chosen

f
or sediment sampling locations, rather
than areas that appeared to be excessively eroded or aggraded. Both sampling locations
were also within 50 meters of the stream gaging locations.
The chosen locations
were
also a com
promise between these characteristics and
locations that could be disguised
from passers
-
by
.
Automated ISCO
s
ampler
s, model

3700,

collected suspend
ed sediment
concentration
samples

from the

two sampling locations
in Tells Creek between March
and July 2011,

and also in October 2011
.

S
tation
1

is located
about 300 meters
upstream

from Ice House Road along Tells

Creek within
about 1 km

of Union Valley Rese
rvoir, at the outlet of Basin
1.
Basin
1
contains
a lower proportion of meadows.
Station
2

is located jus
t below the lower Van
Vleck meadow culvert at the base of the
Basin
2
, which contains a higher proportion

of

meadows
(Figure 1
-
3) (USDA, 2005).


The ISCO sampler has the capacity to collect up to 24 composite, one
-
liter water
samples and contain them withi
n the base of the unit. The sampler utilizes
vacuum

force

to

draw samples into the base of the unit

(ISCO, 1994)
.
Twelve
-
volt

marine batteries

powered both samplers.

A 6
-
inch photovolt
aic sol
ar cell trickle charger was

used to
recharge t
he sampler at Sta
ti
on 1.

Figure 3
-
7 shows the
ISCO sampler installed at Station
1. Figures 3
-
8 through 3
-
10 show complications encountered in various ISCO installation
attempts at Station 2.

39




The ISCO sampler pump intake locations and design were given serious
consideration
due to their influence on suspended sediment representation in the water
column (Eads
and Thomas
, 1983). Given the large variation in flow and th
e high mixing
potential,

the

intake nozzle

at each location
was

moun
ted to the Tells Creek stream bank
in a fix
ed position
, within 0.1 meters from the bed
. It was not feasible to use a depth
proportional device, nor was it
deemed

necessary

at the time of installation

given the high
mixing potential during high flows.


The sampler
s

collected
four

to six

125
-
mL

samples per day

at four to six
hour
intervals
, in a single one
-
liter plastic sam
ple container. The daily

composite
samples were

expected to

capture the potential variation in sediment loads produced during daily flow
variations

without compromising the ba
ttery life
.

Extra room
was provided in each

sample container
to allow

for expansion during freezing events

and to minimize time
spent filtering samples
. The samples were retrieved from each of the two sites once every
two to
three weeks, depending on site
accessibility
constraints
.



40






Figure 3
-
7
: ISCO sampler suction line in Tells Creek,
secured to the bank at Station 1
.



41





Figure 3
-
8
: Snow conditions made access to Station 2 difficult through June, 2011
. Photo
on the left was taken April 3,
2011;

the photo on the right was taken on May 14, 2011.











42



















Figure 3
-
9
: Photo of Station 2 installation location
. Snow conditions made access to the
stream ban
k where Station 2 was

very difficult. Photo was taken April 3, 2011.










43




















Figure 3
-
10
: Tom Eckhardt digging snow for the installation of the ISCO sampler at
Station 2.






44



3.3

Lab

Analyses of Sediment


Every three weeks, samples were tran
sported to the CSUS wet lab for
processing.

Samples were analyzed

for

total suspended solids

using the American Society for Testing
and
Materials

(ASTM) Method D 3977
-
97, Test Method B
-
Filtration (ASTM, 2007).

This method involves pumping all water samples through
glass
-
fiber filter
, evaporating
residual moisture in a low te
mperature

oven

(103
-
105 degrees
Fahrenheit
)
, and weighing

filtered sediment
with the filter
on a

scale
with a precision of

0.
00
01g
rams
.
Pro
-
Weigh
TSS filters were used to filter sediment samples in conformance with the sampling
protocol.
A scale of such pr
ecision was not available for use during this project. A scale
with a precision of 0.01 grams was used instead. This was the only significant
modification

to the testing protocol
.
Filtered sediment mass per volume of sample was
calculated
.
All tools and fa
cilities necessary for successful implementation of this
proc
essing plan were available for use

through the CSUS

Department

of Geology
.

3.4
WEPP
Model


The following explanation of the WEPP model provides background about how
GeoWEPP ultimately uses the WE
PP to interface with GIS and provide
s

watershed
hydraulic assessments in an accurate geographic model environment.


WEPP
is a process
-
based model

developed by the USDA for estimating the
distribution of soil loss on hillslopes at a user
-
specified temporal scale.
Processes
considered in model simulations include rill and interill erosion,
sediment transport and
deposition,
channel flow and erosion,
overland flow, infiltration, transpiration,
evaporation, plant growth and its influence
on
soil hydraulics, plant decomposition,
45



climate, and snow melt.
The model can be applied to a wide range of field condition
s,
including variable topography, forest and

agricultural application, extreme climates,
variable surface and subsurface soil conditions, all across a user
-
specified temporal scale.
Small watersheds modeled with WEPP are represented by
multiple hillslopes linked to
channels

(Flanagan et. al, 1995)
.
Though the m
odel was developed for Horton

overland
flow

conditions
, recent updates to the WEPP model simulate subsurface flow, restricting
bedrock layers, and soil anisotropy (
Dun et. al, 2009
).
Figure 3
-
11

shows
a diagram of
how the WEPP model treats user

inputs.


Overland flow routing utilizes analytical solutions to
the
kinematic wa
ve
equations
along with conservation of mass techniques to calculate peak runoff and runoff
duration.
Sediment detachment, transport, and deposition along WEPP hillslopes occu
rs
when
runoff

shear stress exceeds
soil
critical shear stress.
WEPP computes both soil loss
along hillslopes profiles and sed
iment delivery to the end of

hillslope
s
. These two outputs
consider soil detachment processes
as a function of rainfall intensity

and

r
aindrop impact,
sheet flow,
rill and interill erosion
,

rill and interill runoff rate
,

and sediment transport
capacity. In

addition, channel erosion, deposition, and sediment transport capacity
functions are
also
considered in WEPP watershed applicati
ons (Flanagan et. al, 1995).

Figure

3
-
12 shows an example of the user interface for building a hillslope profile within
WEPP.
Specific
WEPP model components and their
governing equations are described in
their respective sections below.


46




Figure 3
-
11:

Diagram of WEPP user inputs and model representation of the inputs

(Flanagan et. al, 2000).

The “Maps” in this figure represent user input data that, when
combined with climate data, produce an estimate of soil loss for each model cell. The
“Watershed” in this figure shows the components needed to estimate a sediment yield in
an entire watershed
, hillslopes and a conveyance channel. The “WEPP format”

shows
how each hill
slo
pe and channel
has a

specific

length and width
. With these components
defined, the user is ready to “Run WEPP.”


Layers/Inputs

-

Elevation

-

Soils

-

Management

-

Weather


Outputs

-

Discharge

-

Erosion

-

Sed. Yield

-

Storms


47




Figure 3
-
12
: Example WEPP interface.

WEPP uses a simplistic di
agram to represent the
user
-
defined hil
lslope, management practice,

soil type
, and erosion and sediment yield
.




48



Weather

Simulation


WEPP generates daily precipitation, temperature, solar

radiation, and wind speed
using the climate generator, CLIGEN, based on the

Markov chain model

and other
proven generators, EPIC and SWRRB

(Nicks, 1985).
Precipitation is

randomly generated
based on the wet
-
dry probability for each given day in the simula
tion. A skewed normal
distribution is used to determine precipitation volume and monthly mean durations are
used to determine precipitation duration.

Whether precipitation falls as rain or snow, is
based on daily te
mperature minimums and maximums (Flanagan

et al.
, 1995).

Surface Water

Flow on Hillslopes


Hillslope

hydrology functions within WEPP provide
infiltration,
excess rainfall
,
and peak runoff

and duration estim
ates

(Stone et. al, 1995).
The equations below
summarize how WEPP handles each of these hydr
ology components.


Infiltration

-

WEPP

calculates
rainfall
infiltration using the Green
-
Ampt
-
Mein
-
Larson (GAML) equation as modified by

Chu (
Chu,
1978).

User inputs for soil
characteristics such as grain
-
size distribution
and initial soil water content are

utilized in
the WEPP infiltration equations.
Infiltration in WEPP
uses
a form of
equations (3.4)
through (3.6
) below.

f =

K
c

(1 + (N
s
/F))




(
3.4
)

Where F is provided by equation (
3.5
) below,

K
c
t = F
-

N
s

ln

(1 + (F/N
s
))



(
3.5
)

Where N
s

is provided by equation (
3
.6
) below,

49



N
s

= (
ϕ
e



Θ
i
)

ψ




(
3
.6
)

Where


f

= infiltration rate (L/T)


N
s

= effective matric potential (L)


F

= cumulative infiltration (L)


K
c

= effective hydraulic conductivity (L/T)


t

= time (T)


ϕ
e

= effective porosity
(L/L)


Θ
i

= initial soil water content (L/L)


Ψ

= average capillary potential across the wetting front (L)



Runoff

-

Soil

surface topography and soil moisture conditions constrain excess
rainfall calculations within WEPP. Excess rainfall that accumulates

on the surface, when
soil infiltration capacity is maximized, is evaluated against surface storage capacity. This
relationship is used to compute runoff

using equation (
3.7
) below
(Stone et. al, 1995).

S
d

= 0.112r
r

+ 3.1 r
r
2



1.2 r
r
* S
o


(
3.7
)

Where


S
d

=
maximum depression storage (L)


r
r

= random roughness (L)


S
o

= slope of flow

surface (L/

L)



An approximation of
the
kinematic wave model is used to calculate travel time
and the resulting peak runoff (
Stone et. al, 1995). Equation (
3.8
) below summarizes how
the kinematic wave
continuity
equation
for flow on a plane
is solved within WEPP.

50



v = (

h/

t) +

(

q
/

x
)




(
3.8
)

Where the depth discharge relationship is provided by

equation (
3.9
),

q =

h
m





(
3.9
)

Where


v

= rainfall excess

h

=
depth of flow (L)


t

= time (T)


x

= distance from the top of plane


q

= discharge per unit width (
L
3
/
L
*
s)



= depth
-
discharge coefficient


m

= depth
-
discharge exponent


T
he time to kinematic equilibrium, or the time to reach the end of the plane during
co
nstant excess rainf
all

is computed using

equation (3.10
) below.

t
e

= (
L /


v
m
-
1
)
1/m




(
3.10
)

Where


t
e

=
time to kinematic equilibrium
(T)


L

= length of overland flow (L)



= depth
-
discharge coefficient

v

= rainfall excess

m

= depth
-
discharge exponent





51



Water Balance


The WEPP model accounts

for hydrologic processes including evaporation,
transpiration, snow melt, precipitation, and
infiltration

in calculating
the

water balance.
These processes are calculated at 24
-
hour time steps using algorithm
s deve
loped by
Williams et al., 1985,

for the Simulator for
the
Water Resources in Rural Basins
(SWRRB) model.
Equation (
3.1
1)

below summarize
s

how WEPP

maintains a water
balance throughout the model system
, within the WEPP model

(Savabi and Williams,
1995)
.



=

in

+ (P


I) +/
-

S


Q


ET


D
-

Q
d

(
3.1
1)

Where




= soil water content in the root zone (L)



in

= initial soil water in the root zone (L)


P

= cumulative precipitation (L)


I

= precipitation interception by vegetation (L)


S

= snow water content (L)


Q

= cumulative surface runoff (L)


ET

= cumulative evapotranspiration (L)


D

= cumulative amount of percolation loss below root zone (L)


Q
d

= subsurface lateral flow (L)


Surface Cover

and Plant Growth


Plant growth calculations within WEPP are used in
both the water balance and
erosion

components of the model. Variables including root development, canopy height,
52



canopy cover, and biomass production

are used to predict temporal changes in cover
(Arnold et al, 1995). The following equations summarize the
governing equations behind
the plant growth component of the WEPP model.


Equation (
3.
1
2
) below
describes

how heat unit accumulation is calculated for
determining plant development.

HU =
(
(T
mx

+
T
mn
) /
2)



T
b



(
3.
1
2
)

Where


HU

= heat units


T
mx

= maximum

temperature


T
mn

= minimum temperature


T
b

= crop
-
specific base temperature



Plant interception of radiation is estimated using Beer’s law (Monsi and Saeki
,
1953) described in equation (3.13
)
. D
aily biomass production is estimated with equation
(3
.14
)

be
low

(Montieth, 1977)
.

PAR = 0.02092 (RA) * (1


e
-
0.65LAI
)


(3.13
)


B
p

= 0.0001 * BE * (PAR)



(
3.14
)

Where


PAR

= photosynthetic active radiation


RA

= solar radiation


LAI

= leaf area index



B
p

= potential increase in biomass


BE

= crop parameter to co
nvert energy to biomass


53




Canopy cover and
canopy height

influence
raindrop

impact and erosion processes.
B
oth perennial and annual vegetation are modeled

within WEPP
as functions of biomass
as
described

in equations (3.15) and (3.16
) below.

C
c

= 1


e
-

c
B
m




(3.15
)

H
c

= (1


e
-

c
B
m
) * H
cm



(3.16
)

Where



C
c

= canopy cover
,

percent



c

= plant
-
dependent constant


B
m

=
growing season


H
c

= canopy height (L)


H
c
m

= maximum canopy height (L)



The loss of canopy cover, known as senescence, is des
cribed

in WEPP
by the
linear equation (3.17
) below.


C
c

= C
cm

* ((1
-


cs
) / S
p
)



(3.17
)

Where