Sacramento River Basin, California - Defining and evaluating flood management system flexibility, adaptive capacity, and the relationship between these concepts
Sacramento River Basin, California
Defining and evaluating flood management system flexibility, adaptive capacity, and the relationship between these concepts
Sacramento Flood Management System Overview
In the early 1800s, the first settlers to California reported signs of flooding indicating that at times of high flow the Sacramento River would cover a distance five miles on the eastern side and three miles on the west. On almost an annual basis, these colossal volumes of flood water would settle on the valley floor to form an “immense, quiet inland sea a hundred miles long” (Kelley, 1989). Indeed, the Sacramento whose natural flow is around 5,000 cfs for most of the year, could swell to flows as high as 600,000 cfs. Flooding in the over 27,000 square mile basin results from winter and spring rainfall, as well as combined rainfall and snowmelt.
The Sacramento retains little resemblance to its former self. The six major flood control dams in the basin attenuate all but the highest flows, while levees and bank protection restrict river movement and limit overflow to the natural flood basins. However, five weirs along the river allow some overflows into three flood relief basins lining the lower section of the Sacramento. Despite frequent failed attempts to contain the river during high flows, including recent damages from flooding in March 1995 and January 1997, residents and decision makers haven't relented in their efforts to tame the floodwaters and maintain the reclaimed floodplains and marshy islands within the Delta.
Defining and evaluating the term "flexibility" as applied to water management
Discussions around adapting water management systems to future changes often state the need to increase system flexibility, presuming that our current water systems are lacking in these traits. Intuitively, a flexible, easily modifiable system seems desirable when faced with a wide range of uncertain, but plausible future conditions. Yet, despite the frequent use of the term flexibility, very little work has examined what exactly it means to have a flexible water management system; what makes one system more flexible than another; or the extent to which flexibility increases adaptive capacity. Furthermore, the push for more flexibility neglects to consider whether there exists a point after which increase flexibility results in negative impacts, or whether the costs to implement flexible options outweigh the benefit gained from increased flexibility.
This study will review flexibility literature and apply relevant flexibility concepts from manufacturing, information technology (IT), and socio-ecological systems to water management systems. Based on this work, a methodology will be developed for assessing the flexibility of the structural and non-structural components using original flexibility indicators developed in the categories of slack, intensity, and adaptability. The developed methodology for assessing flexibility will then be applied to the Sacramento Valley flood management system.
Assessing current adaptive capacity and the effect of potential management options
The second half of this study will assess the adaptive capacity of the Sacramento Valley flood management system, defined as: the potential or capability of the system to alter to better suit future conditions while still meeting overarching and potentially shifting system objectives (adapted from (IPCC 2007)). Thus, the adaptive capacity of a flood management system is the ability of the system to achieve flood risk objectives under uncertain, changing conditions. It is a function of the range of conditions over which the system can achieve risk objectives, a measure of robustness, in combination with how well and quickly it can adjust to conditions outside this range.
This study will evaluate three often cited drivers of future changes to flood risk, namely: (1) climate induced hydrologic changes, (2) landuse changes in the floodplain, and (3) changes in water management priorities. These impacts, particularly climate induced hydrologic changes and changing management priorities, represent conditions of deep uncertainty. Under conditions of deep uncertainty Lempert, Bankes, and Popper (2003) promote strategies that are robust – “i.e. that perform reasonably well compared to the alternatives across a wide range of plausible scenarios”. Along this line of thinking, this study seeks to determine the range of conditions under which the system can meet flood risk objectives, rather than seeking an optimal strategy for meeting objectives under a particular set of projected future conditions.
Hypothesized relationship between flexibility and adaptive capacity
Intergovernmental Panel on Climate Change (IPCC). 2007. Climate change 2007 : impacts, adaptation and vulnerability : contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change. Ed. M Parry. Cambridge U.K.; New York: Cambridge University Press.
Kelley, R. 1989. Battling the Inland Sea. Berkeley: University of California Press.
Lempert, Robert J., Steven C. Bankes, and Steven W. Popper. 2003. Shaping the Next One Hundred Years. http://www.rand.org/pubs/monograph_reports/MR1626.html.
This material is based upon work supported by the National Science Foundation under Grant No. 0846360.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.