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I I I I I I I I I I ! I I I I I I I I I The basin-level damage estimates are available in spreadsheet form from our website, www.flooddamagedata.org. Estimates are presented by calendar year. The grouping of basins within drainages is somewhat different from that commonly used to define water resources regions (e.g., U.S. Dept. of Commerce, 1978 Census of Agriculture) because, over the years, the NWS sometimes changed its groupings. We developed uniform basin definitions for the full time period by using the following organizational system: (I) Damages are grouped by drainage (e.g, St. Lawrence Drainage, Upper Mississippi, Great Basin) starting in the eastern part of the United States and moving towards the west coast, and then alphabetically by individual or grouped river basin(s). (2) Often, the NWS grouped individual rivers together in annual summaries. For example, damage on the White and Wabash Rivers were usually included together as one estimate. If the published sources of flood data included damage for two river basins together in one year, then data for these two (or more) rivers were added together for all other years. This was the simplest way to produce a coherent data set that could be searched and produce just one row of data for one river basin. (3) In many of the years, damage on unnamed streams was included. If the publication did not give a stream name, damage was included in a row for the drainage called "small streams. " (4) Sometimes the publications would include a river and its small tributaries together, by saying "X River and tributaries." When damage was published in this format, it was entered into the database under the river itself. So, damage listed for some rivers in some years may include not just the river, but its small tributaries (such as creeks). (5) Creeks that were included separately in NWS publications from the rivers to which they are tributaries were entered into the database separately. Creeks can be differentiated from rivers in the database because they are labeled "Cr.,.. whereas rivers are entered with the river name only. An exception to this rule is for rivers with Spanish names, such as the Rio Hondo and Rio Grande. Since users may want to search for "Rio Hondo" rather than "Hondo," "Rio" is included in the database. (6) Users looking for damage information on rivers with branches (such as North Platte, South Platte, and Platte) should look for each of these branches. In some cases, all of the branches of one stream are included together, and in some cases they are not. (7) Several of the streams in the data set cross drainage boundaries. If there is a question about which drainage a stream is in, a user should look in both drainages. E. Use of the Damage Estimates Users of these data sets should be aware that there is uncertainty in the damage estimates, with a likelihood of large errors in some estimates. Types of inaccuracy are described in Section 4, and the magnitude of errors is analyzed in Section 5. In consideration of uncertainty, recommendations regarding appropriate uses of the data are offered in Sections 6 and 7. 19