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ABSTRACT
The Mission Creek watershed was analyzed using Geographical Information Systems (GIS)
as well as field observations. The objectives were to characterize the vital components of
the Mission Creek channel and water, as well as the modes of network evolution. It
contains six unique lithologic units that span an area of roughly 15.71 km2. The watershed
that passes over these lithologic units has a total stream length of 49.5 km, an average
channel slope of 0.30 and a drainage density of 3.15 km-1. Significant locations along the
watershed are detailed to analyze the drainage density, topographic profiles and cross-
sections to provide a framework to regionalize watershed management and stream
resource management. Analysis of drainage density leads to streamflow sensitivity, and
watershed analysis can provide a framework to regionalize watershed management and
stream resource management.
INTRODUCTION
Objectives
The objectives of this study include characterizing vital components of the Mission
Creek channel and watershed including the bed configuration, channel pattern, drainage
network (composition and density) and modes of network evolution. The factors that
control the drainage density are vital to the report. In order to accomplish the extensive
processes that comprise the Mission Creek channel and watershed, strategically chosen
locations in the watershed or at locations heavily influenced by the watershed will be
analyzed.
Study Area
The Mission Creek watershed begins in the Santa Ynez Mountains in Rattlesnake
Canyon, channeling through the city of Santa Barbara, CA, until it empties into the Santa
Barbara harbor. (Figure 1)
Figure 1 – The Mission Creek watershed is located on the southern side of the Santa Ynez Mountain
Range, north of Santa Barbara, California.
It resembles a triangular shape from north to south draining to a singular vertex
(McCuen 1998). The watershed extends roughly 14.2 kilometers from the ocean to the
ridge of the Santa Ynez Mountains with an elevation change of 1.1 kilometers (Clyde 1999).
Rattlesnake Creek is the one main tributary and Mission Creek is the main channel of the
watershed. The area that drains as a result of the Mission Creek watershed is
approximately 15.7 km2 (See Figure 4). Santa Barbara has a Mediterranean climate with
high concentrations of riparian and chaparral vegetation. Alluvial channels have nonlinear
and dynamic tendencies, exhibiting a wide variety of responses to “perturbations of
hydraulic discharge or sediment supply” (Buffington and Montgomery 1999). The
watershed runs through an assortment of residential, urban and natural environments,
making it an integral part of the local hydrologic cycle (Clyde 1999).
DESCRIPTION OF DRAINAGE BASIN
Lagoon
The mouth of the watershed is a blind estuary, which indicates that the system is
open in the winter when rainfall and streamflow are high, yet closed at the mouth by
sandbars during the summer months due to low input of flow. Various processes, both
environmental and anthropogenic, affect the ocean to lagoon access point barrier including
storm flows, waves and human-induced actions. Species that inhabit the lagoon are
predominantly steelhead and tidewater Gobi.
Channelized Reach
The height of the banks extends about five meters. It is built near the harbor to
contain a 10-15-flood with a trapezoidal shape of cement and concrete material. No
boulders, rocks or vegetation are present inside the reach, making the region devoid of
roughness elements.
Oak Park
A channel has been constructed for facilitating fish migration, while also inhibiting
sediment deposition. The streambed varies between gravel, cobble and boulder-sized
sediment. The channel consists of manmade step pools. Boulders have been arranged by
humans, yet they were less in diameter than at Rocky Nook or Skofield parks. All the
reconstruction was done with the goal of establishing a more natural order to the region.
Bankfull indicators include sycamore tree roots. Concrete gabions make up portions of the
bank in some stretches of the river for bank reinforcement preventing bank from migrating.
Rocky Nook
At Rocky Nook Park very large boulders are present from a debris flow. There were
remnants of a paleochannel, as the local area ran along Mission Ridge Fault. Wind and
water gaps, valleys and openings (respectively) where water once flowed through or
carved but had dried up were present. Less fine gravel and boulders than those at Skofield
Park comprise the streambed. They were indications of a river likely established when the
slope was at a lower elevation before the debris flow. A botanical garden nearby is
influenced landscape-wise from an alluvial fan formation of 4-6.25 kya (E. Keller, personal
interview, 2013).
Skofield Park
At Skofield an alluvial fan is present, and the region is also the origin of the 125 kya debris
flow that influenced all the topographically lower region (E.Keller, Personal Interview
2013). A scarp, evidence of a landslide, is present and can be linked to the origin of the
debris flow. Boulders present have the largest diameters observed in the
watershed. Boulders can be termed immobile sediment (Best and Keller 1985). The shape
of the velocity profile is strongly influenced by the size of the roughness elements on the
channel bed. A very high relief and large roughness elements are also relevant geological
elements of the area.
GEOLOGY
The study area is within the Western Transverse ranges, a “tectonically active,
semiarid region characterized by a high rate of denudation”. (Warrick and Mertes 2009)
Heavy influence from geologic and climatic factors results in the distinct variations of relief
and uplift. (Figure 2)
Figure 2 – Digital Elevation Model of Santa Ynez mountain range and Santa Barbara.
Compression from the uplift and lithologic composition generated rapid uplift, producing
abundant east-west thrust faults, folds and strike-slip faults. (Warrick and Mertes 2009)
The formations that comprise the study area range from Quaternary to late Eocene.
The six main geologic units, in order of youngest to oldest, that comprise the
watershed are: Quaternary Alluvium (Qa), Sespe Formation (Tsp), Coldwater Sandstone
(Tcw), Cozy Dell Shale (Tcd), Matilija Sandstone (Tma) and the Juncal Formation (Tjsh).
(Figure 3)
The Qa is landslide debris of unconsolidated alluvium (floodplain deposits of silt, sand and
gravel) deposited during the quaternary period of the last 2.5 mya. The Tsp is a maroon,
red and green silty shale or claystone of interbedded red, tan and gray sandstone of
nonmarine origin and predominantly Oligocene age (geologic epoch from 34-23 MYA). Red
arkosic sandstone and conglomerates at the base of the Tsp formation are interspersed.
The Tcw is a tan, hard, bedded arkosic sandstone with minor interbedding of
greenish-gray siltstone and shale of late Eocene age (geologic epoch from 56-33.9 MYA).
Local oyster shell beds are common, which correlate with the Tcw’s marine origin. The
Cozy Dell Shale is a marine, late Eocene argilaceous to silty micaceous shale of dark gray
color. The Tcd has various light gray to tan arkosic sandstone rocks of Narizian stage origin.
The Matilija Sandstone is of marine origin and late Eocene age (lower Narizian and Upper
Ulatisian stages) with hard, thick bedded, tan arkosic sandstone along with thin partings of
gray micaceous shale. The Tjsh formation is dark, gray micaceous shale with minor thin
interbedding of hard, gray-white to tan arkosic sandstone. The Tjsh is of early to middle
Eocene age.
METHODS
Drainage Density
To determine the drainage density and area, keyhole markup language (kmz)
(zipped files for expressing geographic annotation and visualization) were obtained from
the University of California, Santa Barbara (UCSB) for use in the geographical information
system Google Earth. The drainage density was calculated using the equation:
Drainage Density = Total Length of Streams and Rivers in a Drainage Basin
Total Area of the Drainage Basin
Eight files were obtained from the university. The files show the drainage density,
geologic units, mission creek, mission creek watershed, rattlesnake creek, Santa Barbara
geologic map and a topographical map of Santa Barbara. Microsoft Excel tabular data for
the sum of channel lengths in each geologic unit was also provided by UCSB. Data from
Excel and Google Earth were combined to determine the drainage density.
Topographic Profiles
To determine the topographic profiles (longitudinal and cross-valley), kmz data
provided by UCSB was utilized again in the digital programs Google Earth, Excel and Paint.
An elevation profile was extracted from Google Earth from the longitudinal profile kmz file
and imported to Microsoft Excel. In Excel charts the distance from the ocean and the
elevation above mean level were plotted against each other and lines were constructed to
display the geologic unit boundaries. Cross-Valley profiles were also constructed by using
Google Earth tools and Excel graphs to display onto the application Paint.
RESULTS
Drainage Density and Area
The total stream length of the drainage basin is about 49.5 km with a drainage area
of approximately 15.7 km2. (Fig. 4).
Figure 4 – Mission Creek Watershed, Mission Creek, Rattlesnake Creek, Skofield Park Reach,
Santa Barbara Botanic Garden Reach, Rocky Nook Park reach, Oak Park Reach, Channelized Reach,
Lagoon
The result for drainage density was 3.15 km-1. Drainage densities were also calculated for
each geologic unit and can be seen in Figure 5.
Geologic Unit
Total Stream Length within Unit (km)
Qa 5.8
Tsp 4.7
Tcw 15.1
Tcd 8.5
Tma 7.5
Tjsh 7.8
Watershed Average 49.5
Geologic Unit Area (km2) Drainage Density (km-1)
Qa 1.53 3.79
Tsp 1.93 2.45
Tcw 4.49 3.36
Tcd 2.37 3.60
Tma 2.83 2.64
Tjsh 2.55 3.07
Watershed Average 15.71 3.15
Geologic Unit
Vertical Relief (km)
Qa 0.12
Tsp 0.15
Tcw 0.26
Tcd 0.23
Tma 0.23
Tjsh 0.80
Watershed Average 0.30
Geologic Unit Channel Slope
within Unit Distance From Ocean Along
Longitudinal Profile
Qa 0.055 3.04-3.86 kilometers
Tsp 0.099 Longitudinal Profile Does Not Cross
Tcw 0.12 3.89-4.80 kilometers
Tcd 0.17 4.80-5.15 kilometers
Tma 0.65 5.15-5.46 kilometers
Tjsh 0.7 Longitudinal Profile Does Not Cross
Watershed Average 0.303
Topographic Profiles
The vertical relief calculates the difference between elevation of highest point in the
area and lowest point in the area. The average vertical relief for the watershed is 0.30 km
with the results for each geologic unit in Figure 5. The average vertical relief is the
difference in elevation between the highest and lowest points in a given area. The channel
slope, a measure of the water surface or stream bed slope change in elevation over a
defined distance, of the watershed is 0.25 and the results of each geologic unit can be seen
in Figure 5. The channel slope was measured along the longitudinal profile of Mission
Creek (Figure 6).
Figure 6 – Longitudinal Profile of Mission Creek with Geologic Unit Boundaries
0, 0.0022.41, 0.023
3.62, 0.04
6, 0.08
7.24, 0.15
9.05, 0.23
10.9, 0.37
11.5, 0.46
12.1, 0.53
12.7, 0.61
13.3, 0.76
13.7, 0.84
14.2, 1.1
0
0.2
0.4
0.6
0.8
1
1.2
0 2 4 6 8 10 12 14 16
Elevation above mean sea level
(kilometers)
Distance from Ocean (kilometers)
Longitudinal Profile of Mission Creek with Geologic Units
Qa
Tcw
Tcd
Tma
Cross-valley profiles constructed from Google Earth were created across Mission Creek for
the Coldwater Sandstone and Cozy Dell Shale geologic units (Figure 7).
0, 2212
100, 2145
220, 2075
300, 2050
400, 2025
550, 1990
700, 2062.5
800, 2137.5
900, 2162.5
1950
2000
2050
2100
2150
2200
2250
0 100 200 300 400 500 600 700 800 900 1000
Elevation above meansea level(meters)
Distance (meters)
Cross Section of Mission Creek in Tcw
Figure 7 – Cross Valley Profiles of Mission Creek Coldwater Sandstone and Cozy Dell Shale Formations
0, 1926
100, 1825
175, 1712.5
250, 1675
400, 1551
625, 1650
750, 1700
1000, 1850
1175, 1950
1500
1550
1600
1650
1700
1750
1800
1850
1900
1950
2000
0 200 400 600 800 1000 1200 1400
Elevation above mean sea level (meters)
Distance (meters)
Cross Section Profile of Mission Creek Tcd Unit
Cross-section profile analysis shows the Coldwater unit as slightly more steep than the
Cozy Dell unit.
DISCUSSION
The composite slope distribution (0.30) infers the region in the study can be
classified as to Montgomery and Buffinton’s definition of a cascade channel type.
(Montgomery and Buffington 1997) The cascade channel types exhibits geomorphologic
characteristics such as a boulder bed material; fluvial, hillslope and debris flow as the
dominant sediment sources; a slope of 0.30; and grains and banks as the dominant
roughness elements. It is this distinctive and orderly fluvial geomorphology, some
manmade (Oak Park step-pools) and some natural (Skofield Park debris flow), that
illustrates the complexity of Mission Creek. The cross sections analyzed in the report imply
that the hillslopes upstream have fluctuated according to channel adjustment processes
such as the debris flow. The wide variation in slope influences the entire region (Figure 5),
from determining particle size to the Channelized Reach and the construction of flood-
prevention structures to accommodate.
The Cross-Valley profiles of the Coldwater Sandstone and Cozy Dell Shale have
variances that are clearly evident. Each have similar drainage densities and slopes, yet the
channel bed width for the Tcd formation is approximately 55 meters wide, while the Tcw
formation has approximately a channel bed width of 30 meters. These quantitative values
listed above indicate that one formation has stronger lithologic properties. The Tcw has
the narrower channel bed, leading the supposition that the unit is stronger than the Tcd
formation.
Drainage density indicates how dissected the landscape is by channels, thus it
reflects both the tendency of the drainage basin to generate surface runoff and the
erodibility of the surface materials. Regions with high drainage densities will have limited
infiltration, promote considerable runoff, and have at least moderately erodible surface
materials. Drainage density variations are not as drastic as the slope dimensions (Figure 5),
yet comprise just as significant of an impact on the fluvial geomorphology of the study area.
The Tsp formation has the lowest drainage density (2.45 km-1), which is not a result
of its’ lithologic strength, but of its’ slope, which is the second lowest among the geologic
units (0.099). Of the geologic units with recorded drainage density, the highest was Qa
with a drainage density of 3.79 km-1. The Qa geologic unit is not composed of hard
lithologic material and is the geologic formation with the lowest strength. The Qa unit’s
highest drainage density among the geologic units is compounded by it containing the
lowest slope (0.055). A high drainage density is a sign of a high amount of streams and
tributaries, leading to a relatively rapid hydrologic response to rainfall events; while a low
drainage density infers a poorly drained basin with a slow hydrologic response.
CONCLUSION
The watershed geomorphology is integral in stating the components that constitute
the transfer function. (McCuen, 1998) The impact of the debris flow and westward
movement of Mission Creek by the Mission Ridge fault have vital influences throughout the
watershed, as evident by the paleochannels or change in boulder size, a strong indicator
due to the significant diameter changes. Analysis of drainage density leads to streamflow
sensitivity, and watershed analysis can provide a framework to regionalize watershed
management and stream resource management. The drainage density of the geologic units
varies considerably across the length of the watershed, from 2.45 km-1 to 3.79 km-1. The
area of the geologic units varies from 1.53km2 for the Qa to 4.49km2 for the Tcw. The
channel slope of the geologic units also varies considerably from 0.055 for the Qa to 0.7 for
the Tjsh. The broad range of the watershed characteristics demonstrates the vast
influences that act upon the watershed. The paleohydrologic implications of the region
must be considered when analyzing the watershed due to the variability from the head of
the watershed to the mouth.
While cross-section, longitudinal profiles and drainage density calculations are vital
elements to conceptualization of watershed management, more in-depth geological
analysis of the units incorporating soil permeability, precipitation-soil response analysis,
groundwater influence and strength of the rock. These factors are as key to watershed
management and incorporation would likely lead to a more comprehensive understanding
of the Mission Creek Watershed’s distinctive characteristics.
References
Best, D. W., & Keller, E. A. (1985). Sediment storage and routing in a steep boulder-bed
rock-controlled channel. Retrieved from
https://gauchospace.ucsb.edu/courses/file.php/7452/Readings/Best_et_al._1985.pdf
Buffinton, J. M., & Montgomery, D. R. (1999). Effects of sediment supply on surface textures
of gravel-bed rivers. Water Resources Research, 35(11), 3523-3530. Retrieved from
https://gauchospace.ucsb.edu/courses/file.php/7452/Readings/Buffington_Montgomery_
1999b_WRR.pdf
Keller, E. (2013, April 6). Personal interview.
McCuen, R. (1998). Hydrologic analysis and design. (2nd ed., p. 100).
Upper Saddle River, NJ: Prentice-Hall, Inc.
Santa ynez mountains and santa barbara. (2009). Retrieved from
http://www.geog.ucsb.edu/~joel/g148_f09/lecture_notes/transverse_ranges/santabarbar
a2_persp.jpg
URS Greiner Woodward-Clyde. (n.d.). South coast watershed characterization study: An
assessment of water quality conditions in four south coast creeks. (1999). Retrieved from
http://sbprojectcleanwater.org/Documents/Water Quality Reports/scwc.final.pdf
Viveen, W. W., Schoorl, J. M., Veldkamp, A. A., van Balen, R. T., Desprat, S. S., & Vidal-Romani,
J. R. (2013). Reconstructing the interacting effects of base level, climate, and tectonic uplift
in the lower Miño River terrace record: A gradient modelling
evaluation.Geomorphology, 18696-118. doi:10.1016/j.geomorph.2012.12.026
Warrick JA, Mertes LAK (2009). Sediment Yield from the tectonically active semiarid
Western Transverse Ranges of California, Geol Soc Am Bull 121: 1054-107
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