Water Storage Vs Flood Management Changing Priorities

Shriner and Street (1998) recognize potential "critical supply-demand mismatches" in regions like California that combine long dry seasons with high dry-season water demands. Flood-control concerns could exacerbate this problem. Climate models suggest stronger and more frequent flood episodes as a result both of stronger precipitation events as well as shorter periods between snow deposition and snowmelt. Water storage and flood management are linked because key facilities used for flood management, dam/reservoir systems, typically also serve water-storage goals. A conflict in traditional dam/reservoir management priorities potentially arises. To provide a flood-protection role, reservoirs are drawn down (or not completely filled) in anticipation of heavy inflows. But with declines in the water-storage period provided by snowpack, reservoirs will have to be filled sooner (corresponding with earlier snowmelt), and greater emphasis will have to be placed on maintaining full reservoirs in anticipation of longer dry seasons, even if flood events remain a possibility before the dry months of summer arrive. In short, the flood-control role played by multi-purpose dam/reservoir systems during mid- to late-spring may have to be de-emphasized in comparison with the water-storage role. This perspective on reprioritizing the different roles of multifunction dam/reservoir systems differs from the California Energy Commission's (CEC, 1989) expectation that flood control will continue to be emphasized with a resulting increase in the risk of late-summer water shortages in California, as well as from McAnally et al. (1997), who generally call for keeping reservoir water-levels lower in response to increasing vulnerability to flooding.

A de-emphasizing of the flood-control role played by major water-storage facilities, given the potential for more frequent flood events, suggests that alternative flood-management methods will have to be pursued. By the late

1980s, roughly 75% of California communities contained land that lies within Special Flood Hazard Areas or floodplains vulnerable to 100-year floods (CEC, 1989). Among the alternatives (and complements) to reservoir capture of flood water are:6

Enhancing watershed management. This includes re-establishment or preservation of upland forests, reconnecting stream channels with extended riparian zones (wetlands), and avoiding the dredging or channelizing of streams.

Pre-designating flood zones. Such zones, typically in agricultural or open-space/park regions, would be diversion regions for flood waters before they reach urban lands. Ideally, flood zones would also serve as aquifer-recharge zones, but a region's topography and geology may not align effectively.

Restricting flood-plain development. This intervention in local economic development has historically been resisted since flood plains appear to present low-cost opportunities for new residential and business development. Enforcement of existing flood-plain building restrictions often lapses during extended periods of normal and below-normal flows. However, since such intervals between major floods may become shorter in the future, existing restrictions on flood-plain development could be re-emphasized and new restrictions added.

Requiring flood insurance. Flood insurance serves to spread the economic impacts of flood-related disasters to large numbers of homes and businesses and allows affected areas to recover more quickly. Homes can be rebuilt and businesses reopened more quickly with less localized economic loss if they are insured against floods. Currently, flood insurance is not profitable for private-sector insurance companies, so it is offered instead by the federal government. If the government cannot find ways to induce the private sector to provide this service, it should nevertheless continue to offer it and, in some cases, require it for individuals and businesses located in Special Flood Hazard Areas.

Preparing in advance for flood-emergency management. Upstream gauging stations linked electronically to emergency-service providers (rescue crews, etc.), combined with up-to-date evacuation plans and a prepared populace, can greatly diminish losses of human life during a flood event, reduce discomfort in the flood's aftermath, and accelerate the recovery process. Numerous federal and state agencies and numerous information systems, such as ALERT (Automated Local Evaluation in Real Time), already exist and can be utilized or deployed in regions whose flood risks increase in the coming decades (Water Education Foundation, 1998).

Interest in these and other similar measures is likely to increase should climate change result in the combination of earlier snowmelt and increased frequency and magnitude of flood events. Instead of the current philosophy of flood control, one can imagine a new philosophy (actually, a return to the older philosophy) of flood management. Costs involved would combine structural enhancements and non-structural adaptations, but would depend in their details and magnitude on how Californians balance the conflicting objectives of flood control and late-summer water supply.

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  • akseli
    Why is water use and flood control have conflicting demands in canada?
    9 days ago

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