California Hydrography
The demand for use of hydrography in California for visualization and mapping, as well as for a common spatial base for in-depth analysis of multiple datasets, is increasingly becoming more prevalent in fisheries management and conservation. To fulfill this need California Department of Fish and Wildlife, Pacific States Marine Fisheries Commission, and it’s partners have continued to strive to utilize newly available products and technology to develop more accurate higher resolution hydrographic products to our staff and constituents. These CalFish pages will introduce you to California Hydrography products, plus give you some ideas on how you might utilize these products for your next project.
California Hydrography Products
CalHydro 100k
The legacy California Hydrography product is called CalHydro 100k. CalHydro 100k is a medium resolution stream hydrography covering the State of California. Funded by the
California Legacy Project and the
CDFW Fisheries Branch and completed in 2003, Calhydro 100K has been used widely over the years not only for mapping, but extensively as a spatial index for fisheries management project data such as field observation locations, salmon abundance trends, fish passage barriers, habitat restoration projects, and many others. Based on the United States Geological Survey (USGS) National Hydrography Data set (NHD) Medium Resolution hydrography, CalHydro 100k presents streams as measured linear features giving it the advanced ability to give associated data an “address” that can be logically compared to other addresses on the stream.
California Streams
Since the introduction of CalHydro 100k, the increasing demand for higher resolution hydrography for fisheries management along with a tremendous effort by USGS to complete a nationwide high resolution NHD, has resulted in DFG’s California Streams data set. Introduced in early 2012, California Streams was developed on the same premise as CalHydro100k, providing measured streams based on NHD High Resolution linework at 1:24,000 scale or better. As High Resolution NHD was being developed, many of the CalFish and CDFW programs migrated their indexed data from Calhydro 100k to the higher resolution data. Now that California Streams is available, the migrated data can now be transferred to the stream routes provided by California Streams. Also, CDFW survey, assessment and monitoring programs are already adopting California Streams as their base hydrography. On a side note, USGS promotes NHD as an ever improving hydrography data set by continually increasing the resolution and horizontal accuracy of their features, utilizing mostly localized information that is processed through their
stewardship program. As a result, CDFW plans to periodically update California Streams to reflect NHD improvements and keep the data set as up to date as possible. Note that version 3 of California Streams is now available for viewing on the CalFish map viewer as well as for download from CalFish Data Downloads. Please read the metadata for detailed information on the version 3 update.
California Lakes
Companion to the stream hydrographies, CDFW’s California Lakes is the culmination of many years of waterbody mapping by the CDFW. For sure, California Lakes has had a more varied past than the streams data sets, but is coming together as California’s comprehensive waterbody layer for natural resource management. Initially developed in 2007, California Lakes is also being increasingly used as a spatial index for fisheries management and conservation data. In combination with California Streams, the potential for meaningful interaction between these two surface hydrographies is possible.
Using Routed Hydrography as an Index
Anything that occurs in:
a wet or dry stream or stream bed
lake or lake bed
crosses over, under, or through a stream or lake
is located on, near, or follows the streak path or lake shore on either or both sides
occurs in a watershed or drainage area that includes the stream or lake
can be indexed to routed hydrography and given an address or range of addresses on that hydrography.
This might be thought of as similar to assigning a house a street address or a city block a range of street addresses. The process of assigning these addresses is referred to as ‘linear referencing.’ Once indexed, these data are stored in a table as ‘events’ of either locations (point events) or ranges (linear events) and can be displayed on a map using their addresses. The term for this process of displaying events is called ‘dynamic segmentation.’
Indexing data along routed hydrography is a more intuitive way to describe associated locations than are geographic coordinates. Describing the location of a bridge as 500 meters upstream on a creek is normally more intuitive than describing it as lat Y and long X. The bridge is inherently associated with the creek and it’s location should be described as such if possible.
Hint: A waterbody or watershed polygon can be indexed using routed linear hydrography that courses through (intersects) the waterbody by indexing all or a portion of the intersecting route(s). If indexed data affects only a portion of the polygon, the polygon can be displayed to represent the affected area while only routes intersecting the affected area are indexed.
Analyzing Indexed Data with a Hydrography Network
California Hydrography not only provides stream addresses, but it also capable of simulating a connected network of watercourses and waterbodies and can hold attribute information for that network such as stream gradient, morphology, flow volume, temperature, temporal variations and more. Connectivity between streams in the network enables ‘flow’ from one stream to another that can be analyzed by “tracing” upstream or downstream on the network from and to user-specified locations.
“Analyzing the relationship of events in a hydrography network can lead to important conclusions regarding cause and effect in the landscape… With network position and flow established, it is possible to use operators to determine relationships in terms of route, sequence, distance, time, and value. For example, it is possible to find diversions upstream of a streamgage, look at the trend in sequenced pH values, determine the distance between water sampling sites, calculate the time of travel between a chemical spill and a drinking water intake, or find all species downstream of a construction site.” Jeff Simley – USGS
Tools and methods for analyzing relationships among datasets are traditionally reserved for a working GIS environment. More and more, though, widely available mapping applications such as ArcGIS Server web applications, Google Earth and Maps and others will be used to visualize and examine hydrography data and analyses. Use an ArcGIS Server web application to mark your projects along streams and record the address on that stream. Use Google Earth to fly along the path a salmon might swim upstream to spawn. Use another web application to investigate the amount of upstream habitat opened by the removal of a barrier.