Category Archives: Hydrologic Data

Hydrologic Data Products Now Available

We’re excited to announce the release of a suite of hydrologic data products.

Clockwise from upper left – flow direction, flow accumulation, stream centerlines, and orthophotos (image by Quantum Spatial)

These Sonoma County hydrologic data products were produced in fall 2015 and winter 2016 from the countywide 2013 LiDAR data. The hydrologic products include a set of vector deliverables and a set of raster deliverables. Vector products include stream centerlines, confluence points, hydroenforcement burn locations, and watersheds. Raster products include flow direction, flow accumulation, and a hydroenforced bare earth digital elevation model (DEM). Hydroenforcement of a DEM imparts the true elevations of culverts, pipelines, and other buried passages for water into a Digital Elevation Model, creating a DEM suitable for modeling the flow of surface water.

The extent of the deliverables is all of Sonoma County, the Lake Sonoma watershed in Mendocino County, and the Lake Mendocino area.

These hydrologic datasets are a mostly-automated first step in the eventual development of a ‘localized’ or ‘LiDAR enhanced’ National Hydrography Dataset (NHD). They are suitable for landscape level planning and hydrologic modeling. These data products do not contain a guarantee of accuracy or precision and – without site specific validation and/or refinement – should not be relied upon for engineering level or very fine scale decision making.

The hydrologic data products were produced by Quantum Spatial. Read Quantum Spatial’s Sonoma County Hydroenforcement Technical Data Report.

The individual hydrologic data products are described briefly below.

Vector Hydrologic Products (available here as a file geodatabase)

  • Stream Centerlines – Centerlines of streams in Sonoma County. An area of flow concentration is considered a stream if its flow accumulation (upstream catchment area) exceeds 5 acres and a clearly defined channel exists. Where possible, stream centerline names (GNIS_Name) are consistent with the NHD.
  • Hydroenforcement Burn Locations – Line features that represent locations where hydroenforcement occurred.
  • Confluence Points – Points that represent stream intersections (confluences).
  • Watersheds (HUC2 through HUC14) – Watershed boundaries for nested hydrologic units from HUC 2 (region) to HUC 14 (sub-watershed). Where possible, watershed names are consistent with the NHD. Watershed mapping conventions follow those for NHD’s Watershed Boundary Dataset (http://nhd.usgs.gov/wbd.html).

Raster Hydrologic Products (1-meter resolution – available as watershed downloads)

  • Hydroenforced Digital Elevation Model – The Hydroenforced DEM is the LiDAR derived (2013) bare earth DEM with contours, pipelines and other buried passages to water ‘burned in’, so that the DEM correctly models surface water flow.
  • Flow Direction Rasters – Values in a flow direction raster represent one of eight directions (pixel values range from 1 to 8); No Data represents areas where there is no flow off of the pixel (sinks).
  • Flow Accumulation Rasters – Flow accumulation is a measure of upstream catchment area. Pixel values in a flow accumulation raster represent the cumulative number of upstream pixels (in other words, the count of pixels that contribute flow to a given pixel).

The webmap below shows the HUC 12 watersheds and the stream centerlines.