A GIS Approach to Understanding the Yolo Bypass

Diana Craft

American River College

Geography 350: Data Acquisition in GIS

Fall 2010

ABSTRACT

Landsat imagery and GIS data obtained online, along with other online research, were used to examine aspects of the Yolo Bypass, including its extent, uses, hydrology, geographical context, and seasonal changes. ArcGIS was used to create a series of maps displaying the results of this examination.

INTRODUCTION

Just west of the Sacramento River, I-5’s Elkhorn Causeway to the north and I-80’s Yolo Causeway to the south cross a large expanse of flat land that comprises a quilt-like array of leveed fields, sometimes flooded by rain or irrigation. I’ve driven over this land on my way to school and back to Woodland and have wondered about the seasonal changes I’ve observed in what I assumed was the Yolo Bypass. How is this land used? How much of it actually is the Yolo Bypass? What happens when it floods? I decided to find data that would help me understand the Bypass—its extent and use, how it changes over the seasons, and how it is used for flood control—and create a series of maps to serve as a basis for future investigation.

BACKGROUND

The Yolo Bypass is a 59,000+ acre engineered floodway that is part of the Sacramento River Flood Control Project. Its sources are the Colusa Basin Drain (via the Knights Landing Ridge Cut), Willow Slough, and Cache and Putah Creeks, and it receives diverted water from the Sacramento and American Rivers via the Sacramento Weir (involving manual operation of up to 48 steel gates) and from the Sacramento and Feather Rivers and the Sutter Bypass via the passive Fremont Weir (where water spills over when the crest is reached).

It incorporates seasonal agricultural areas (mostly rice fields in the Northern Bypass, north of 1-80; other crops include corn, melons, tomatoes, safflower, and milo) and seasonal and permanent wetlands that provide significant wildlife habitat, including the 16,770-acre Yolo Bypass Wildlife Area between Davis and West Sacramento and several duck clubs to the south (CA Dept. of Fish & Game et al, 2008).

Fig. 1. Historic map of the Yolo Basin, 1903–1910 (DFG et al, 2008).

The overlap of agriculture, managed wildlife habitat, and recreation through the seasons in way that is compatible with flood protection make the Bypass unique. Situated within the naturally formed Yolo Basin (Fig. 1), once an almost 80,000-acre wetland (DFG et al, 2008), the Yolo Bypass was engineered in the early 1900’s to channel floodwaters away from Sacramento and other low-lying areas. Wetlands restoration by the Army Corps of Engineers led to the 1997 dedication of the Wildlife Area (DFG et al, 2008). (Fig. 2)

Fig. 2. The Yolo Bypass Wildlife Area on a rainy day, Dec. 2010.

The 41-mile long Bypass has a capacity that is 4.5 times greater than that of the lower Sacramento River, and it serves as the primary way to drain the Sacramento Valley during major flood events. (Yolo Bypass Working Group et al, 2001). It is lined with levees ranging from 7,000 to 16,000 feet apart, except for an eight-mile levee-free section below Putah Creek (where the higher elevations can contain all but extreme flooding). These levees guide floodwaters down to the Sacramento-San Joaquin Delta. The Bypass floods seven out of ten years some time during the period of October through June, with peak flooding in January through March, and it is also intentionally flooded during dry years to maintain fish populations (Smalling et al, 2005).

METHODS

I started with Landsat TM imagery, available at no cost from the USGS’s Global Visualization Viewer (GLOVIS) web site. These images are remotely sensed digital photographs taken by Landsat satellites that provide data collection in repeated coverage of the Earth’s surface, as part of a program jointly managed by NASA and the USGS. Using coordinates from Google Earth to get the path and row of imagery that would include the Yolo Bypass, I downloaded and preprocessed images from different times of year, including one from January 2006, when there was significant flooding in the Bypass. These images provided visual information for digitizing a polygon of the Bypass area, and the January 2006 image would serve as backdrop for a map showing flood features.

Next I looked for GIS datasets that would help me build the maps. Yolo County’s website didn’t have accessible data, and my call to their GIS Specialist went unanswered; instead I obtained Yolo County data from the Sacramento Area Council of Government’s Regional GIS Clearing House. The USGS’s National Hydrography Dataset (NHD) provided a geodatabase of complex hydrologic data, including watershed data, and I discovered ArcGIS’s Utility Network Analyst toolbar specifically designed for analyzing geometric networks like the NHD flowlines dataset that shows direction of water flow. Other sources yielding useful data were the California Department of Water Resources (DWR) Land & Water Use Data Collections and the Yolo Natural Heritage Program. (Links for all websites are listed in References).

I looked in vain for data that accurately described the boundaries of the Bypass, and I ended up making my own polygon using the Landsat imagery and an average of information gleaned from one dataset, PDF maps from various groups, and—surprisingly, my most detailed resource—a paper map from AAA.

I visited the Yolo Bypass Wildlife Area twice to take photographs between rainstorms, and I talked to a ranger at the California Department of Fish and Game (DFG) Yolo Bypass Wildlife Area Headquarters who gave me useful information about the Bypass boundaries, including pointing out on a blown-up photograph the section that does not have a levee.

Online research provided an overwhelming amount of information in the forms of land management plans and strategies for both the Bypass and the subset of the Wildlife—so much information, in fact, that distilling it down to a manageable background for the project was a challenge. Many organizations and governmental entities are invested in the management and future of the area, including the Yolo Basin Foundation, Yolo County, DWR, DFG, and US Fish and Wildlife Service.

RESULTS

Map 1 Map 2

Map 1 introduces the polygon that describes the boundaries of the Yolo Bypass and places it in local context, showing county boundaries, nearby cities, and the highways and railroads that cross the Bypass. Map 2 shows the Bypass polygon over a true-color Landsat image of the area, taken Oct. 1, 2010.

Map 3

In Map 3, the Bypass is placed in regional hydrologic context, showing it in relationship to the Sacramento River Watershed (hydrologic sub-region from the NHD data) and the legal boundaries of the Sacramento-San Joaquin Delta (as defined by Section 12220 of the Water Code).

Map 4 shows the direction of water flow into and from the Bypass, with directional arrows

that were activated in the NHD flowlines layer when I viewed the NHD data in ArcGIS’s Utility Network Analyst. The general flow is from the sides and above the Bypass (from higher elevations to the north and west, and from channeled/diverted water to the east); water then moves down the Bypass (mostly along the Tule Canal and Toe Drain which run along its east side) and into the Sacramento-San Joaquin Delta.

Map 5 shows inflow sources and flood control features of the Bypass over a Landsat image
taken January 23, 2006, when the Bypass was flooded. The image bands have been assigned to color channels in an R=4, G=5, B=3 combination that better delineates areas of water (the smaller image shows a true-color version of the flooding). Notice how the floodplain allows the water to spread out for slow drainage into the Delta, while the Sacramento River stays within its path.

Fig. 3. Comparison of monthly Landsat images of the Yolo Bypass region, showing seasonal change over the years 2008 (Row 1), 2009 (Row 2), and 2010 (Row 3). (Images for some months were not available.)

The GLOVIS site is designed to make it fairly easy to view images before choosing and downloading, and I took advantage of this by making screenshots of three years’ worth of monthly Landsat images. This enables a side-by-side comparison of imagery for each month (where available and not cloud-covered), showing seasonal patterns for 2008–2010. (Fig. 3)

ANALYSIS

I was able to find data that allowed me to build maps showing the geographical extent of the Yolo Bypass, as well as its water sources, direction of flow, and flood control features, and to place the Bypass in a larger context in relationship to the Sacramento-San Joaquin Delta.

However, it was hard to find definitive data describing the Bypass boundaries. The GIS data and maps I found had boundaries that greatly differed (mostly at the upper and lower boundaries and in areas not clearly defined by levees or county lines), and most were over generalized. So I made my own polygon for the Bypass area, kind of a visual average of the best information I could find, and am calling it a work-in-progress, to be updated as I find better, authoritative data on the boundaries.

I barely dipped into the complex NHD data for the Bypass and don’t pretend to have a full understanding of the water dynamics of the Bypass, but the data established a starting point for such an examination, and ArcGIS’s Utility Network Analyst allowed me to use the NHD data to show direction of water flow, a pretty amazing feature when figured out.

Screenshots of satellite imagery provided a picture of seasonal changes over time, and I found the most interesting aspect was how much the seasonal patterns are unchanged, year after year. (I know the predictable nature of these changes is basic to our understanding of seasons, but still it surprised me to see just how closely a given month’s images correlated to those in other years.)

The January 2006 Landsat image of a flooded Bypass provided a useful backdrop for understanding the Bypass’s flood control features, and it is clear that the design of the Bypass (levees and canals) take advantage of its natural, historical function as floodplain.

CONCLUSION

Many interests and users overlap in the Yolo Bypass. Wildlife habitat restoration and protection (the Bypass is part of the Pacific Flyway bird migration route), recreational users from bird watchers to hunters, farms and ranches with historic family names, as well newer agricultural operations (with rice farming a $50 billion a year industry for Yolo County)—all overlay the Yolo Bypass’s primary function as flood protection facility. They co-exist or give way to each other in seasonal rotation, and they all are trumped by the heavy rains and flooding of the Sacramento Valley winter. The Bypass is a rich and diverse subject for study that could be approached in many ways, and I plan to revisit it for future projects, building on the foundation laid here.

It’s a timely topic: The Yolo Bypass has been in the news in recent days, as what the Sacramento Bee characterized as a “habitat land rush” is on, with at least one developer pushing through a deal that may amount to speculation on the value of habitat mitigation for the proposed Bay Delta Conservation Plan, and local authorities hastily signing on to obtain surface water rights for Woodland and Davis (Sangree and Weisner, Sacramento Bee, Dec. 19, 21, 2010).

REFERENCES

PUBLICATIONS AND INTERNET RESOURCES

California Department of Fish and Game, Yolo Basin Foundation, and EDAW, 2008.
Yolo Bypass Wildlife Area Land Management Plan. (Internet) (http://dfg.ca.gov/lands/mgmtplans/ybwa/)

Lillesand, T.M., R.W. Kiefer, and J.W. Chipman, 2008. Remote Sensing and Image
Interpretation. Sixth Edition, John Wiley & Sons, Inc.

Milliken, J., M. Shin, and R. Neal, 2000. A Cooperative Project to Create Agricultural
Field-Boundary Databases in GIS—California. 2000 Esri International User Conference. (Internet) (http://proceedings.esri.com/library/userconf/proc00/professional/papers/PAP388/p388.htm)

Sangree, Hudson. “Habitat land rush worries rice farmers”: Sacramento Bee, Dec. 19, 2010.

Smalling, K.L., J.L. Orlando, and K.M. Kuivila, K.M., 2005. Analysis of Pesticides in Surface
Water and Sediment from Yolo Bypass, California, 2004–2005: U.S. Geological Survey Scientific Investigations Report 2005-5220, 20 p. (Internet)
(http://ca.water.usgs.gov/user_projects/toxics/YoloBypass.html)

U.S. Environmental Protection Agency: Surf Your Watershed

(http://cfpub1.epa.gov/surf/locate/index.cfm)

Water Resources Association of Yolo County, 2007. Integrated Regional Water Management Plan. (Internet) (http://www.yolowra.org/irwmp_documents.html)

Weiser, Matt. “Why Yolo Bypass Is Prime Turf”: Sacramento Bee, Dec. 21, 2010.

Yolo Bypass Working Group, Yolo Basin Foundation, and Jones & Stokes, 2001. A Framework for the Future: Yolo Bypass Management Strategy. (Internet) (http://yolobasin.org/)

DATASETS AND IMAGERY

California Department of Water Resources: Land & Water Use: Land & Water Use Data
Collections (http://www.water.ca.gov/landwateruse/lwudatacoll.cfm)

Sacramento Area Council of Government: Mapping Center: Regional GIS Clearing House.
(http://www.sacog.org/mapping/clearinghouse/)

U.S. Geological Survey: National Hydrography Dataset (http://nhd.usgs.gov/data.html)

U.S. Geological Survey: USGS Global Visualization Viewer (http://glovis.usgs.gov/BrowseBrowser.shtml)

Yolo Natural Heritage Program: Maps, Data, and Documents. (http://www.yoloconservationplan.org/maps-and-documents.html)