Title
Is Natomas area still in Flood Risk?
Author

Name: Oksana Grinevich
American River College, Geography 350: Data Acquisition in GIS; Fall 2017
Abstract

In February, 1986 in Sacramento, for 11 days nearly 10 inches of rain fell. The floodwaters destroyed levees in Natomas area during that time. But still many homes were built since then.
As it mentioned in SacBee on January 12, 2017, according to Rick Johnson, SAFCA’s executive director, “$2.4 billion worth of flood-control projects are still on the drawing boards. They include plans to widen the Sacramento Weir and Yolo Bypass, to address lingering levee problems on the major rivers and to complete repairs to the levees ringing the Natomas basin, whose vulnerabilities prompted the city to halt new construction from 2008 to 2015.” Should we still be building there today?

Introduction

The original idea of this project, was to analyze the land cover of the city Natomas, CA, and show if this area is still in danger of flood loss compare to 1986 year by using flood depth data. According to MavensNotebook.com, Natomas “was built in 1912 to 1914 by a private company that bought 75% of the acreage in Natomas for $1 an acre”. Since then, some major floods happened, including one in 1986. Is this area still in danger condition? Is any levee's improvement happened during last decade? What was done to save lives, properties or businesses? I want to see if new flood occures what neighborhoods in that area will be in danger.
Background

While taking one of Geography class I was shocked to open for myself that Natomas area, known as "Dead valley" was drained and rebuilt after huge flood in 1986. In February, 1986 in Sacramento, for 11 days nearly 10 inches of rain fell. The floodwaters destroyed levees in Natomas area during that time. So many houses were built since that and homeowners in that neighborhood are paying high rate flood insurance. Would it better to use high insurance rates for improoving the areas' levees?
Methods

 

  • Imagery for Natomas area was obtained from ESRI base map.
  • The Natomas flood 1986 photo was obtained from www.safca.org
  • The Ultimate Flood Depth was obtained from City of Sacramento and converted from .pdf to .jpeg format.

  • Parcels shapefile was added from County of Sacramento.
  • I georeferenced the image with using control points and the georeferencing tool bar in ARCMap.
Results
After georeferencing Flood Depth and adding Pacel data I see high population where flood risk and flood depth are the worst.

my green map
my map
Analysis
From the first map it is easy to see that my study area (in violet color) could be under +16 feet of water. And on the third map it shows that evacuation routes will be impossible to use after 16 hours!!!!

The map below shows that condition of levees in my study area is "usage certification expired". Those areas are reliant on levees for flood control. The levees in my study area are not in good condition and are not be able to protect the community.
Conclusions

After analyzing Flood Depth, Levees’ Condition, and Evacuation route data, I have an opinion that Natomas area still has a high risk of flooding even improvement of levees has been done since 1986. According to cityofsacramento.org, “After re-evaluation of the levees by the US Army Corps of Engineers, FEMA remapped the Natomas Basin area into a floodplain with an AE flood zone designation in December 2008.  The AE flood zone designation required elevating or flood-proofing structures at or above the 100-year floodplain, which would be up to 20 feet in some areas.” Also, the article mentions Natomas has an A99 flood zone designation since June16, 2015. It means, according to cityofsacramento.org, those rates are “significantly higher than the “Preferred Risk Policy” rates.” So, it is better for home owners in the high risk areas, as Natomas, to carry flood insurance and to plan for emergencies.

References
  • City of Sacramento, 2009. Flood Depth, Maximum Flood Depth, and  Levees condition. City of Sacramento Geographic Information Systems Website http://www.cityofsacramento.org
  • ESRI, 2017. Imagery base map. Environmental Systems Research Institute
  • Washburn, Tim, March 28, 2003. Tim Washburn on the history and future of Sacramento’s flood control system. Maven’s Notebook http://mavensnotebook.com/2013/03/28/mavens-minutes-tim-washburn-on-the-history-and-future-of-sacramentos-flood-control-system-2/.
  • Sacramento Area Flood Control Agency (SAFCA), 2009. Natomas Flood 1986 photo. http://www.safca.org
  • Dale Kasler, Phillip Reese and Ryan Sabalow, January 12, 2017. After years of drought, Sacramento confronts an old foe: Flood risk.Sacramento Bee http://www.sacbee.com/news/state/california/water-and-drought/article128114694.html