The flood next time....
s we watch the strongest hurricane ever seen by scientists in the eastern Pacific dissipate, we should pause and reflect on the flood history of San Diego. It hasn't happened recently or often, but floods do occur and some are big. This information may be surprising for the homeowners and businessmen who have recently moved to the city and live and work in the flood plains. If flood damage does occur, who pays? The taxpayers of San Diego and the nation not the people who made it happen.
As we look at our creeks and waterways we see exotic weeds clogging the channels, replacing attractive trees such as sycamore and willow. We see rusty abandoned shopping carts and trash to highlight their lack of care. Yet the small streams and rivers that flow through San Diego are critical for storm water drainage. If we repaired and restored them, we could enhance the quality of urban life, save money, reduce the cost of public health problems, reduce flood risk and damage, and maximize the economic and ecological benefits of the services they provide. If they remain ignored and unloved, we can expect extremely costly damage will occur.
The San Diego River watershed covers a large area. In the past, when it was less urbanized than today, the San Diego River experienced several very large floods and many minor ones. Mission Valley was often full, bank to bank, and cut off all travel for several days at a time. The heavy rains of 1862 inundated most of California and filled much of the Central Valley. The heavy rains and overgrazed hills led to massive floods that flushed out the creeks and rivers of Southern California. The Santa Ana River peaked at 317,000 cfs (cubic feet per second; a cubic foot is about 8 gallons). This is more than 7 times the volume of the recent flood generated on the Colorado River to scour the river and create new sand bars.
The San Diego River only reached a third this size, but at 94,500 cfs (which would completely fill Qualcomm stadium every couple of minutes) it was an awesome flood. The smaller flood of 1916 was also impressive and did considerable damage. Even the 1927 flood was significant, and it is worth noting that the last long dry spell like the current one occurred in 1927.
Photo taken on February 2, 1927 shows the Old Town railroad bridge washed out by the flood. This rail right-of-way still exists - you can see it looking east from I-5; Friars Rd. runs underneath it. Needless to say, if a similar flood happened today, you just might see the top of a large semi truck stuck on Friars. Photo: San Diego Historical Society, photo collection.
Partly in response to the flooding, and in a futile effort to meet local drinking water needs with local resources, dams have now been built on several of the streams that feed the river and on the river itself. This provides an increase in flood protection, but in 1980 San Diego's reservoirs were all full and spillways were running as a major storm approached. Fortunately, at the last minute it swung through Baja instead of San Diego. If it had hit San Diego, the damage would have been in the billions of dollars.
Sadly, many of the benefits of these dams are offset by the effects of urbanization. As we build houses, offices, roads and parking lots, we increase the land area that is impervious to water. As a result, the rain has no way of entering the soil. Soil compacted by equipment and revegetated with weeds also retains much less water than undisturbed ecosystems. Rather than being held and moved into the ground, a high proportion of the rain quickly runs off into streams, causing more frequent and greater flooding than existed in the natural watershed.
Research has shown clearly that floods may become six times larger; high water levels that previously occurred only once every 100 years (on average) in an unurbanized setting may now recur every 10 to 20 years. A rainfall greater than the 100-year event can have catastrophic effects.
The effects of urbanization can be readily observed in Mission Valley a flood disaster waiting to happen. The City of San Diego should take aggressive steps to limit its liability for the inevitable flooding that will occur.
Imagine what will happen when we have a big rain storm, like many in the past. The flows at Santee in 1862 were almost 30 times higher than in the very expensive flood of 1980. While upstream dams will capture some of the water, increases from urban runoff may offset these benefits, and flood damage in Mission Valley will be very extensive and costly. Estimated peak flow in Mission Valley (including the protective effects of El Capitan and San Vincente Reservoirs) is 80,000 cfs.
Yet the channel capacity is far less than that. Why? To put it simply, rain is rain and floods are floods, but politics is politics. Pressure for development has repeatedly overwhelmed common sense and prudence. Many well-intentioned people have failed to look at the historical record and the results of research on the effects of urbanization on flooding. Ignorance is bliss only until it rains.
The history of flood control capacity shows what happened. The floodwater planners of the Corps of Engineers were under no political pressure in 1950. They could calculate a realistic storm flow and plan according, estimating Mission Valley peak flows of 115,000 cfs. They might choose an inappropriate solution (concrete and more concrete), but at least they were conservative. As Mission Valley land became increasingly attractive for development and memories of the floods of 1938, 1937 and 1927 faded, so did consideration of flood flows.
In 1959, when the Town and Country Hotel was built, channel capacity was reduced to only a few thousand cfs. It soon became clear that this wouldn't be enough. By 1971, the city was requiring channel capacity for a 50-year flood with a calculated volume of 36,000 cfs. Subsequently, the capacity has been increased to 49,000 cfs. But this remains little more than half the potential flood flow for a 100-year storm. And, there are 1,000 year storms out there waiting to happen.
Clearly, the City and County of San Diego and other local cities should have developed watershed and water way planning many years ago. The goal of these efforts should be to protect the public treasury and taxpayers from preventable costs and to promote the public health, safety and welfare. Waterways in their natural form are irreplaceable community assets with considerable value to present and future generations. They provide critical ecosystem services with very high dollar values that have been historically neglected. They also provide ecological, recreational, educational and aesthetic benefits. Taxpayers should refuse to pay for stupid behavior.
The objectives of this effort should be to:
Watershed planning should be done throughout the area. The first and most important step in planning should be a careful determination of the economic benefits of improved management policies. This could be done by calculating the costs of past flood events (what was lost, who lost, who paid) and estimating the potential costs of a future large flood. Historically, development has been heavily subsidized by public taxpayers, who foot much of the bill for providing services and infrastructure for development and then pay the costs of the impact generated by these activities.
By the same token, developers should not be used as a deep-pocket payer for city activities that are unrelated to development. Users should pay for their activities.
Storm water control technology should be installed as a normal part of all development activities. To protect Chesapeake Bay, the state of Maryland requires no net change in storm water runoff after development. We should do no less. Like Maryland, we should have a storm water park, showing homeowners, developers and engineers how these infiltration beds and retention systems work. Retaining the water on site would also reduce irrigation costs and improve base flows in these much degraded streams and rivers. We should also enact much more stringent erosion control policies and recover costs for sediment that clogs drains, gutters and creeks when erosion control is neglected.
Let the San Diego City Council and County Board of Supervisors know that you are sick of paying for other peoples' mistakes! Demand storm water planning and improved erosion control now. Ask for a watershed program to protect our pocketbooks, our health and our environment.
|David Bainbridge is the coordinator of environmental studies at United States International University in San Diego, and has been an adjunct faculty member at SDSU for almost ten years. He has a BA degree in Earth Sciences from UCSD and a MS degree in Ecology from UC Davis. He has written more than 250 articles and 6 books, including The Straw Bale House (Chelsea Green). This article is based on notes prepared for his class: San Diego: The regional environment and a draft management plan for Carroll Creek.|