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