This 1997 report was prepared for the Washington State Department of Ecology. It underscores how wetlands on private land can benefit the larger community, and how infill can pressure wetlands in a way that increases flood risks. Highlights include (emphasis added):
See also:
EPA: Wetlands and Flood Protection
Wetlands within and downstream of urban areas are particularly valuable, counteracting the greatly increased rate and volume of surface-water runoff from pavement and buildings.
The Why Files: Wetlands and floods
[Charles River, Massachusetts…] After calculating the cost of creating that amount of storage with dams, Larson says the Corps concluded it “would be a lot less expensive to buy 8,000 acres of natural wetland, and to use conservation restrictions to buy up development rights” on other floodplain acreage.
Northampton’s Flood and Natural Hazard Mitigation Plan: Floyd Flood Damage Reported Behind View Avenue; Avoid Building on Filled Wetlands
One of the “Priority Actions” is to “Consistently enforce the Wetlands Protection Act to maintain the integrity of the 200’ riverfront area, wetlands and wetland buffer areas.”
The Economic Value of Wetlands: Wetlands’ Role in Flood Protection in Western Washington
…Episodic flooding along rivers and streams in the lowlands of Western Washington has become a recurrent theme of recent years. Development practices that eliminate or compromise natural systems capable of controlling runoff appear to be exacerbating flooding problems in many areas. This highlights the importance of the remaining natural systems capable of attenuating flood flows, particularly wetlands, in the region’s defenses against increasingly destructive floods.
To economists the problem of protecting wetlands for the flood protection services they provide is complicated by the “public goods” character of wetlands. Although wetlands provide diverse valued services to humans, the incentives that private property owners have to protect wetlands may nevertheless remain low. Wetlands owners can neither easily capture the social benefits that accrue when wetlands are protected nor produce those benefits independent of the cooperation of many others in pursuit of the same goals. Traditionally government is looked to for wetlands protection as a result…
The analysis suggests that communities are likely to pay an increasingly high price for flood protection if they allow their remaining natural systems capable of attenuating flood flows to become further compromised in their ability to do so…
Attitudes toward wetlands have changed enormously over the past several decades. Formerly regarded as nuisances, wetlands are increasingly valued today for the wildlife they support and the numerous other amenities they provide. Nevertheless, wholesale conversion of wetlands to other uses occurred as settlement expanded across the nation, and wetlands continue to be under development pressure in many areas…
More than half of the wetlands that once existed in western Washington have been lost. Often the cause has been agricultural conversion, but today wetlands are increasingly at risk due to urban and suburban development. Western Washington is now one of the fastest growing regions of the country, and the remaining wetlands in rapidly developing areas are increasingly valuable for the flood protection they can provide. At the same time, the increasing pace and density of development is resulting in the natural wetlands systems that are capable of absorbing urban runoff becoming ever more fragmented, even as the need for flood protection grows ever more critical…
The results of the analysis we did of the Lynnwood and Renton systems gave similar values which, when annualized to $/acre/year, are comparable to values found in the few other economic studies that have been done of the value of wetlands for flood protection. We produced three estimates of “whole system” wetlands value for flood protection, which range from about $36,000/acre to about $51,000/acre. These values reflect both the current efficiencies of wetlands in their unaltered state to attenuate flood flows and the relatively high cost of adding to this capacity, a result of the degraded state of many remaining wetlands. The analysis of the North Scriber Creek wetland’s value for flood flow attenuation revealed somewhat lower values, ranging from $8,000 to $12,000 per acre. This lower value is consistent with expectations, based as it is on benefits that are more local in character and on the relative cost efficiency with which additional storage capacity can be added to this particular wetland…
Building structures or filling within floodways confines flood flows to narrower channels and causes increased flood heights and rates. Studies have shown that flood peaks may be as much as 80 percent higher in watersheds without wetlands than in similar basins with large wetland areas (U.S. ACOE 1976)…
See also:
EPA: Wetlands and Flood Protection
Wetlands within and downstream of urban areas are particularly valuable, counteracting the greatly increased rate and volume of surface-water runoff from pavement and buildings.
The Why Files: Wetlands and floods
[Charles River, Massachusetts…] After calculating the cost of creating that amount of storage with dams, Larson says the Corps concluded it “would be a lot less expensive to buy 8,000 acres of natural wetland, and to use conservation restrictions to buy up development rights” on other floodplain acreage.
Northampton’s Flood and Natural Hazard Mitigation Plan: Floyd Flood Damage Reported Behind View Avenue; Avoid Building on Filled Wetlands
One of the “Priority Actions” is to “Consistently enforce the Wetlands Protection Act to maintain the integrity of the 200’ riverfront area, wetlands and wetland buffer areas.”