Is Sacramento in Danger of a Catastrophic Flood?
By Eric Huston
03/15/2011
Intermediate GIS Final Project UCLA
03/15/2011
Intermediate GIS Final Project UCLA
Abstract: Sacramento is located at the confluence of the Sacramento and American rivers. About 215 square miles of Sacramento County are located on the 100 year old floodplain of the Sacramento river. The area is used to flooding but what would happen if Folsom Lake Dam happened to fail? Using ArcGIS, we can calculate an assessment of what would happen to Sacramento and the surrounding areas if this were to ever happen.
Introduction:
The Capitol of California, Sacramento is located at the confluence of the Sacramento River and the American River. Located at roughly 38 degrees North and 121 degrees West, Sacramento is situated in the northern portion of the Sacramento- San Joaquin Central Valley. Built on a floodplain, the city is used to its fair share of regularly seasonal floods from its two main rivers. The Sacramento River flows North to South from the Klamath Mountains to Suisun Bay, an arm of the San Francisco Bay (1). It is the largest river in California and has been known to flood. There are historical accounts of flooding dating back to the 1800's. While the Sacramento River does not pose such a threat unless a ferocious storm is behind it, the American River does unfortunately.
The American River flows East to West from the Sierra Nevada mountain range into the Sacramento River. The river is divided into several forks and is dammed in two locations relatively close to each other. The Folsom and Natomas dam, located roughly 20 miles or more from downtown Sacramento are used to regulate the flow of the river (2). However, the majority of the water is stored at Folsom Lake which is about 26 miles East of Sacramento. The dam has been used as a major roadway leading into the city of Folsom but all of that changed after 9/11. After the 9/11 terrorists attacks, the Bureau of Reclamation's Safety of Dams Program closed down the road that went across the dam and raised security as it was proposed as a terrorist's target. The road on the dam has not been reopened and since it was a main road that went into the city of Folsom, it was decided to build a separate bridge instead named Folsom Lake Crossing.
Methods: Using ArcGIS, I created two maps to show potential flood hazards in Sacramento. The first map shows the general terrain features of the region. While the main purpose is to assess flood damage, it is very important to understand the geographical terrain in a region to see why and how flooding will occur in a region.
This map was created using a Digital Elevation Model (DEM). The DEM was obtained from the USGS Seamless server by selecting Sacramento, Placer, and El Dorado Counties to get a full picture of Folsom Lake and Sacramento. By using ArcGIS, several unique spatial analysis tools were performed to create the map.
After downloading the DEM, I uploaded that data into ArcGIS and gave the the data a unique color ramp to make the terrain more identifiable. Next, slope was calculated but had to be reclassified due to ArcGIS creating too many values. After the slope had been reclassified, I created a Hillshade of the terrain to give the terrain some depth. Lastly, I did a raster calculation of the Hillshade and Slope to show which areas of the terrain would be the most susceptible to flooding. Sacramento is in a valley meaning the terrain is fairly flat which makes it even more susceptible to flooding. Furthermore, since the American River flows East to West, this means the Water is flowing from an elevation much higher than Sacramento giving it more speed as it flows down into the Sacramento river.
Using various forms of data from the UCLA GIS Database and Tiger, I obtained shapefiles of the Sacramento and American rivers, a layer of streets in Sacramento, and state and county shapefiles to help viewers locate the region. Next, I had to delete several lakes, ponds, and little streams in the water shapefile so a buffer would only go around the rivers. However, I noticed that the Sacramento River was all one feature and I knew that the portion of the river above the confluence would not flood since water can not flow against another current. Furthermore, Folsom Lake itself was posing as a problem because buffers kept being created around the lake. The lake itself cannot flood if it is losing water so I had to delete that too. Once I edited the data for my preference, I created a multiple layer buffer of half a mile, one mile, and two miles around the American River and the portion of the Sacramento River that flows south from where the rivers converge. Lastly, I selected all the streets that were inside the buffers to show that these streets would be severely at risk given these buffers.
Results:
From the Physical Terrain Map-
After creating the two maps we see there is a clear relationship between areas with a very small slope (flatland) and flooding. Areas of land that have a very low slope and display a small hillshade are far more susceptible to flooding than areas with steep slopes and high hillshades. These areas of land are also far more vulnerable to soil erosion which can cause flooding to be even greater.
From the Flood Hazard Map-
A majority of Sacramento would be in serious danger of a devastating flood. Almost the entire downtown region of Sacramento would be flooded. Most of the major streets would be closed or have flood damage to them. An entire neighborhood, known as "The Pocket" which lies about two to three miles south of downtown Sacramento would be severely flooded as it is very close to the Sacramento River. Lastly, almost all the neighborhoods that border the entire extent of the American river would be greatly in danger. An evacuation plan could be implemented but I fear this would be very improbable due to how fast the water would reach Sacramento. There would not be enough time for people to evacuate.
Conclusion:
From my analysis of the Sacramento region, I have concluded and confirmed with other studies that Sacramento probably has the highest flood potential in the entire U.S. If Folsom Dam were to fail or be destroyed, a vast amount of water would rush down the American river and take out almost anything in its path. The majority of downtown Sacramento would have severe flood damage and several communities that are located along the river would probably be engulfed by the river. Even homes that are situated high on the levees would not be completely safe. They might be protected from the rushing water but they would be in greater risk due to massive soil erosion caused by so much water traveling at such high speeds. The best preventive measures for Sacramento are to keep maintaining the levees on its river banks and to keep up security on the Folsom Dam. During the catastrophe, evacuation routes and/or procedures should be implemented however an evacuation route seems implausible because the water would reach downtown Sacramento in about 30 minutes or less. I would suggests that maybe two or more of Sacramento's skyscrapers be designated as an evacuation building to reach a safe height from the flood. Sacramento is in a good location for a city but it may not have been a good idea to have built Folsom Dam so close to such a large city. Studies such as this one can be applied to other regions of the world such as China's three gorges dam therefore flood hazards are essentially a con associated with dams, especially when they are located only 25 miles or more away from a heavily urbanized area such as Sacramento.
References:
"Sacramento River Picture, Facts & History – Sacramento, CA." Famous Wonders of the World: Best Places to Visit, See Travel Pictures. Web. 15 Mar. 2011.
Introduction:
The Capitol of California, Sacramento is located at the confluence of the Sacramento River and the American River. Located at roughly 38 degrees North and 121 degrees West, Sacramento is situated in the northern portion of the Sacramento- San Joaquin Central Valley. Built on a floodplain, the city is used to its fair share of regularly seasonal floods from its two main rivers. The Sacramento River flows North to South from the Klamath Mountains to Suisun Bay, an arm of the San Francisco Bay (1). It is the largest river in California and has been known to flood. There are historical accounts of flooding dating back to the 1800's. While the Sacramento River does not pose such a threat unless a ferocious storm is behind it, the American River does unfortunately.
The American River flows East to West from the Sierra Nevada mountain range into the Sacramento River. The river is divided into several forks and is dammed in two locations relatively close to each other. The Folsom and Natomas dam, located roughly 20 miles or more from downtown Sacramento are used to regulate the flow of the river (2). However, the majority of the water is stored at Folsom Lake which is about 26 miles East of Sacramento. The dam has been used as a major roadway leading into the city of Folsom but all of that changed after 9/11. After the 9/11 terrorists attacks, the Bureau of Reclamation's Safety of Dams Program closed down the road that went across the dam and raised security as it was proposed as a terrorist's target. The road on the dam has not been reopened and since it was a main road that went into the city of Folsom, it was decided to build a separate bridge instead named Folsom Lake Crossing.
Methods: Using ArcGIS, I created two maps to show potential flood hazards in Sacramento. The first map shows the general terrain features of the region. While the main purpose is to assess flood damage, it is very important to understand the geographical terrain in a region to see why and how flooding will occur in a region.
This map was created using a Digital Elevation Model (DEM). The DEM was obtained from the USGS Seamless server by selecting Sacramento, Placer, and El Dorado Counties to get a full picture of Folsom Lake and Sacramento. By using ArcGIS, several unique spatial analysis tools were performed to create the map.After downloading the DEM, I uploaded that data into ArcGIS and gave the the data a unique color ramp to make the terrain more identifiable. Next, slope was calculated but had to be reclassified due to ArcGIS creating too many values. After the slope had been reclassified, I created a Hillshade of the terrain to give the terrain some depth. Lastly, I did a raster calculation of the Hillshade and Slope to show which areas of the terrain would be the most susceptible to flooding. Sacramento is in a valley meaning the terrain is fairly flat which makes it even more susceptible to flooding. Furthermore, since the American River flows East to West, this means the Water is flowing from an elevation much higher than Sacramento giving it more speed as it flows down into the Sacramento river.
Using various forms of data from the UCLA GIS Database and Tiger, I obtained shapefiles of the Sacramento and American rivers, a layer of streets in Sacramento, and state and county shapefiles to help viewers locate the region. Next, I had to delete several lakes, ponds, and little streams in the water shapefile so a buffer would only go around the rivers. However, I noticed that the Sacramento River was all one feature and I knew that the portion of the river above the confluence would not flood since water can not flow against another current. Furthermore, Folsom Lake itself was posing as a problem because buffers kept being created around the lake. The lake itself cannot flood if it is losing water so I had to delete that too. Once I edited the data for my preference, I created a multiple layer buffer of half a mile, one mile, and two miles around the American River and the portion of the Sacramento River that flows south from where the rivers converge. Lastly, I selected all the streets that were inside the buffers to show that these streets would be severely at risk given these buffers.Results:
From the Physical Terrain Map-
After creating the two maps we see there is a clear relationship between areas with a very small slope (flatland) and flooding. Areas of land that have a very low slope and display a small hillshade are far more susceptible to flooding than areas with steep slopes and high hillshades. These areas of land are also far more vulnerable to soil erosion which can cause flooding to be even greater.
From the Flood Hazard Map-
A majority of Sacramento would be in serious danger of a devastating flood. Almost the entire downtown region of Sacramento would be flooded. Most of the major streets would be closed or have flood damage to them. An entire neighborhood, known as "The Pocket" which lies about two to three miles south of downtown Sacramento would be severely flooded as it is very close to the Sacramento River. Lastly, almost all the neighborhoods that border the entire extent of the American river would be greatly in danger. An evacuation plan could be implemented but I fear this would be very improbable due to how fast the water would reach Sacramento. There would not be enough time for people to evacuate.
Conclusion:
From my analysis of the Sacramento region, I have concluded and confirmed with other studies that Sacramento probably has the highest flood potential in the entire U.S. If Folsom Dam were to fail or be destroyed, a vast amount of water would rush down the American river and take out almost anything in its path. The majority of downtown Sacramento would have severe flood damage and several communities that are located along the river would probably be engulfed by the river. Even homes that are situated high on the levees would not be completely safe. They might be protected from the rushing water but they would be in greater risk due to massive soil erosion caused by so much water traveling at such high speeds. The best preventive measures for Sacramento are to keep maintaining the levees on its river banks and to keep up security on the Folsom Dam. During the catastrophe, evacuation routes and/or procedures should be implemented however an evacuation route seems implausible because the water would reach downtown Sacramento in about 30 minutes or less. I would suggests that maybe two or more of Sacramento's skyscrapers be designated as an evacuation building to reach a safe height from the flood. Sacramento is in a good location for a city but it may not have been a good idea to have built Folsom Dam so close to such a large city. Studies such as this one can be applied to other regions of the world such as China's three gorges dam therefore flood hazards are essentially a con associated with dams, especially when they are located only 25 miles or more away from a heavily urbanized area such as Sacramento.
References:
"Sacramento River Picture, Facts & History – Sacramento, CA." Famous Wonders of the World: Best Places to Visit, See Travel Pictures. Web. 15 Mar. 2011.
"Sacramento Flood History." SAFCA :: Sacramento Regional Flood Control Agency. Web. 15 Mar. 2011. .
