Organizing for Endangered and Threatened Species Habitat Draft

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toward construction of a"reasonable and prudent" alternative. The Fish and Wildlife Service's objectives centered around using enhanced river flows to recover presently listed species, to prevent future listings of additional species, and to provide sufficient habitat for conservation of the natural biological ecosystem. A team of people representing the Fish and Wildlife Service and the National Biological Survey had created a table of target flows that cumulated into the 417,000 acre foot estimate based on an assumption that inadequate stream flows, and most especially the lack of peak and pulse flows were the most important limiting factors in the Platte River Basin ecosystem. Therefore, quantities o.f water must be enhanced by an annual average of 417,000 acre feet. Re-organized water quantiti.es would be required to recover critical habitat components including channel roosting habitat, wet meadow habitat, sandbar nesting habitat, fishery habitat, and foraging habitat. All these coniponents were seen as essential for recovery of all federally listed species and over 300 migratory bird species in the Central Flyway. The Fish and Wildlife Service held that flow conditions on the Platte River affected the habitat components directly. Re- regulated flows would recover damaged habitat, prevent the need for listing additional species, and provide for conservation of the natural biotic ecosystem components. The FWS identified pulse fllows as the highest priority. They were viewed as essential to maintain and enhance the physical structure of wide, open, unvegetated and braided channels, to supply soil moisture and pooled water during the growing season for plants and animals lower in the food chain in meadow grasslan3s, to rehabilitate and sustain biologic webs in main and side channels as nursery habitats for fisll, shellfish, and other aquatic organisms, and to facilitate nutrient cycling in floodplains. Pulse flows also raise groundwater levels in wetlands adj acent to rivers and bring organisms close to the soil surface for predation by migratory birds and other species. Pulse flows contribute to the break-up of winter ice and thereby induce the scouring of vegetation off sandbars, which is especially important in years of low flow. Except for the driest of years, at ieast 50% of the pulse flows should occur during May 20-June 20 and should emulate traditional flow patterns of 10 days ascending, 5 days cresting, and 12 days descending (LJ.S. Fish & Wildlife Service 1997). To accomplish all this, FWS biologists an.d hydrologists called for an average annual increase of flow volume at Grand Island, Nebraska, in the amount of 417,000 acre-feet-this to add to the existing flow pattern that had emerged over the twentieth century. Target volumes were categorized by dry years, normal years, and wet years. Decisions for what kind of year managers would be facing were expected to be based on esi:imated gross water supply, plus estimates of groundwater and precipitation, and snowpack in the entire basin (Bowman 1994). The quantity of 417,000 acre-feet of water was cali.brated using actual flow patterns from 1943-1994. Target flows were calculated by looking at days when flows were short of the desirable standard as defined by the FWS, the differences between the observed and desirable were averaged, and then cumulated into the over-all target flow value. Water users did not agree with the numbers presented by the Fish and Wildlife Service's biological opinion. They believed that 417,000 a.cre-feet of water for habitat recovery was not based on logic, history, or even river capacity. In the often heated discussion of target flows, even basic facts about the physical structure of the river could not be agreed upon, especially the most 59