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DAM REMOVAL 257 Table V. Research components of the environmental assessment of dam removal and dam retention alternatives for Rodman Dam by the St Johns River Water Management District Research component Estimated cost and responsibility Research efforts assessing the physical and chemical environment: River transect surveying Bathymetric and sediment depth mapping Hydraulic and hydrological modelling Sediment properties and erodibility characteristics Sediment characteristics, toxics and seedbank analysis Inundated floodplain analysis Sediment transport modelling Sediment resuspension due to wind Sediment loading to the river below the dam Surface water quality analysis Groundwater impacts of drawdown $130000 (contractual) $176000 (contractual) $90 000 (agency effort) $10000 (contractual) $58 000 (contractual) $35000 (contractual) $69 000 (agency contractual effort) $5 000 (agency effort) $5 000 (agency and contractual effort) $44000 (agency and contractual effort) $5 000 (agency effort) Research efforts assessing the biological and ecological environment: Fish populations assessment $24000 (contractual and gratis agency effort) Migratory fish populations analysis $22000 (contractual) Aquatic plant populations and management (gratis agency effort) Bird populations assessment $45 000 (agency effort) Threatened and endangered species and species of special concern $17000 (contractual and gratis agency effort) Floodplain forest succession modelling $55 000 (contractual and agency effort) Habitats assessment $10000 (agency effort) temperatures are sometimes higher in impoundments; they may be reduced below dams through hypolim- netic withdrawal (Baxter, 1977; Walker, 1979; Ward and Stanford, 1989). Fish species composition invari- ably changes due to impoundment, as riverine assemblages are replaced by lacustrine ones (Hynes, 1970; Welcomme, 1979; Meffe, 1984; Boschung, 1987; Li et al., 1987; Ross, 1991). Bird communities often change following impoundment and wildlife populations are frequently affected as well (Nilsson and Dynesius, 1994). The loss or alteration of floodplain wetlands after impoundment is typical, and may be significant in regions where floodplain forests are rare (Lugo and Brown, 1984; Potter and Drake, 1989; Romme and Brack, 1991; Larson, 1991; Dynesius and Nilsson, 1994). Threatened and endangered species are some- times impacted by impounding a river (Potter and Drake, 1989; FERC, 1991; Sklar, 1992; Cone, 1993; Pal- mer, 1994), but not always in a unilateral manner (Townsend and Crowl, 1991). Habitat fragmentation and changes in wildlife usage invariably occur due to impoundment (Dodd, 1990; Dynesius and Nilsson, 1994; Nilsson and Dynesius, 1994). There are few published reports of biological and ecological assessments for proposed dam removals; only the proposed Elwha and Glines Canyon Dam removals have extensive assessments predicting biological and ecological impacts of dam removal. In that case, the FERC completed a draft EIS of various retention and removal alternatives (FERC, 1991). Often, the primary biological concern is fish migration, and the pre- dicted outcome of dam removal is obvious (e.g. Woolen Mills Dam, Salling Dam, Columbia Falls Dam, Edwards Dam, Elwha and Glines Canyon dams). The environmental assessment approach designed by the St Johns River Water Management District for the proposed Rodman Dam removal can be divided into two basic groups of research components: (1) efforts assessing the physical and chemical environment: and (2) efforts assessing the biological and ecological environment (Table V). It is important to understand that these research efforts are directed to provide the Florida Legislature with the information necessary to make a decision on whether to remove the dam. If they decide for removal and restoration of the river, then additional research and assessment will be necessary to prepare dam removal and river restoration plans. In all likelihood, an EIS would be required as part of the permitting process. The assessment studies outlined in Table V would provide a