ArcGIS REST Services Directory

Layer: Designated Floodways (ID: 19)

Parent Layer: Floodways

Name: Designated Floodways

Display Field: Stream

Type: Feature Layer

Geometry Type: esriGeometryPolygon

Description: The Designated Floodways in this dataset are derived from the Designated Floodway Maps on the CVFPB ftp site. The scanned Designated Floodway Maps are available as .tifs on the ftp site. These scanned images were georectified using reference points, when available, that matched reference points on the current Bing aerial imagery service. Due to the resolution and quality of the scanned images, the lack of orthorectified base imagery on the scans, and/or changed ground conditions, many of the Designated Floodway maps are not able to be reconciled precisely with current ground conditions. Therefore the boundaries represented in this feature class represent the closest approximation possible of the Designated Floodways drawn on the scanned Designated Floodway Maps. There are instances where levee centerlines in the California Levee Database (DFM_CALeveeDatabase_v22_R2_20110128_93.mdb) are coincident with the designated floodways drawn on the scanned images. In these cases the surveyed levee centerlines in the CLD were used to determine the respective boundaries of the designated floodways. There are surveyed levee centerlines in the database that diverge from the designated floodway boundaries drawn on the scanned images; these surveyed lines were not used and the lines on the scanned images were digitized to represent the designated floodway boundaries. Additionally, there are levee centerlines in the CLD that were created using other methods including heads-up digitizing. These lines may or may not have been incorporated into the designated floodway feature class depending on their accuracy and proximity to the designated floodway lines drawn on the scanned images. The Notes field indicates designated floodways that incorporate portions of the CLD levee centerlines into this feature class.There are instances where the scanned images could not be precisely reconciled with current ground conditions but the designated floodways appear to be coincident with features visible on the current aerial imagery such as roads or levees that likely define the floodways. In these instances the designated floodways have been digitized while referencing the feature apparent on the aerial in conjunction with the designated floodway on the scanned image rather than directly from the scanned image.Sheets S43-S46 were not found for the Tuolumne River, Mitchell Road to Whitmore Road reach in Stanislaus County. The designated floodway has been approximated in this area based on the the western terminus of this reach on the preceding sheets, the eastern terminus of the San Joaquin River to extension of Whitmore Road reach, and the current Bing aerial imagery service.The scanned images for Cottonwood Creek in Tulare County from Cross Creek to Grapevine Creek included A and B zones; these have both been included in the digitized designated floodway feature class. The scanned images for Mokelumne River in San Joaquin and Sacramento counties included portions of the 100 year floodzone estimated boundary outside of the designated floodway boundaries; these have been included in the designated floodway feature class and noted as such. No sheets were found for the Yuba River in Yuba County on the CVFPB ftp site other than an index sheet. The designated floodway for this reach has been digitized from the index sheet and incorporates surveyed levee centerlines from the CLD as its outermost boundaries. The index also includes Areas A, B and C within the outermost boundaries; these areas in the feature class are based on the designated floodway lines drawn on the scanned index. Attribute information for this dataset is from the Designated Floodway Program.

Copyright Text: Atkins, 2011.

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