California Interagency Watershed Mapping Committee

History of IWMC and CalWater

Contents

US Geological Survey (USGS) Hydrologic Unit Maps
Hydrologic Unit Mapping in the Natural Resources Conservation Service (NRCS)
History of Interagency Watershed Mapping Committee (IWMC) and CalWater

Hydrologic Unit Mapping in NRCS -California
How is CalWater being used

USGS Hydrologic Unit Maps for the United States

In the mid 1970's the US Geological Survey (USGS) Office of Water Data Coordination (OWDC), under the sponsorship of the Water Resources Council (WRC), developed a nationally uniform hydrologic unit (HU) system. The Hydrologic Unit Maps series were published in 1978 at the 1:500,000 for each state, and described in USGS Water-Supply Paper 2294 (Seaber, P.R., Kapinos, F.P., and Knapp, G.L., reissued 1987, Hydrologic Unit Maps: U.S. Geological Survey Water-Supply Paper 2294, 63 p.) The report provides a complete list of all the hydrologic units, along with their drainage areas, their names and the names of the States or outlying area in which they reside.

This system divides the country into 21 Regions, 222 Subregions, 352 Accounting Units, and 2,149 Cataloging units based on surface hydrologic features. A hierarchical hydrologic unit code (HUC) consisting of 2 digits for each level in the hydrologic unit system is used to identify any hydrologic area of interest.

You may still order a print copy of both the maps and Paper 2294 report from the USGS. Digital versions of the maps, and metadata, are available for download from the USGS (scroll down to online linkage).

New Draft Interagency Guidelines on Delineation of Watershed and Subwatershed Hydrologic Unit Boundaries are being developed by the USGS Water Information Coordination Program , and the FGDC (Federal Geographic Data Committee) Subcommittee on Spatial Water Data (also called the Advisory Committee on Water Information).

Hydrologic Unit Mapping in NRCS

The NRCS (formerly known as the Soil Conservation Service) has a long history of hydrologic unit and watershed mapping.

    The 70's

    In 1978 the NRCS, formerly known as the Soil Conservation Service (SCS), issued a policy that all resource inventories and surveys were to be coded with and capable of being retrieved by HUCs. NRCS decided to build on the USGS HU Mapping system. NRCS refers to the Accounting Unit (6 digit) drainage as a basin and the Cataloging Unit (8 digit) as a subbasin.

    At about the same time, SCS initiated a national program to further subdivide HUCs into watersheds for use in water resource planning. An extension of 3-digits was added to the 8-digit HUC to designate a Watershed. An 11-digit Watershed HU is typically 40,000 to 250,000 acres in size. By 1982, SCS manually mapped the Watershed boundaries in nearly all states using 11-digit identification codes.

    The 80's

    In the 1980's, several SCS state offices began subdividing the Watersheds into subwatershed categories for use in natural resource, water quality, flood damage, and progress reporting activities. This resulted in adding either 2 or 3-digits to the SCS 11-digit code. Most subwatersheds are typically 10,000 to 40,000 acres in size.

    The 90's

    In the 1990's NRCS began to transition the paper map data into the digital realm. The NRCS originally distributed a delineating and digitizing criteria document (NI 170-304) in 1992 and revised and redistributed it as a working draft in June 1995. The working draft has continued to be updated and is available as the current NI 170-304 along with a summary of updates made since June 1995.

    The methodology described in the national instruction is designed to be used to construct the hydrologic unit maps in the NRCS National Hydrologic Unit database. Mapping scale is 1:24,000. The digitizing captures the watersheds (11 digit) and subwatersheds (14 digit) hydrologic units nested within the Cataloging Units (basins) as defined by the United States Geological Survey, (USGS) in earlier publications. The final product is to be a seamless, digital coverage, by state, meeting national map accuracy standards (NMAPS).

History of IWMC and CalWater

Early NRCS Efforts

The institutional memory (institutional memories means interviewing long time NRCS staff people who were there at the time, including Walt Sykes, Essie Johnson, Robin White, Mike Whiting, and others) of the NRCS Hydrologic Unit mapping effort in California goes back to about 1978, when a member of the Water Resources Planning staff hand drew the 11-digit 250,000 acre watersheds on the USGS 1:500,000 map. Apparently this was in response to a call from National Water Resources Planning to identify the 250,000 acre watersheds for reporting and accounting. Blue line and mylar masters were made of this map.

Then in about 1995 (or perhaps earlier -- written records are missing), again in an effort to comply with requests from NRCS National Headquarters (NHQ), the understanding is that this earlier USGS 11-digit HUC map (1:500,000 with re-delineated 010 watershed boundaries) was plotted with a digital version of our counties and rivers, and printed out as wall size blue line and mylar masters at a 1:1,000,000 scale. There is no record of these 11-digit watersheds ever being digitized. It was probably based on this, that we reported to NHQ that we had delineated to the 11-digit level. However, the attempt to combine these two sets of maps did not align well, and the California State Office at that time did not have the personnel or the Geographic Information System (GIS) expertise to fix it. The effort was abandoned as we joined a Statewide mapping effort described below.

Early Coordination of NRCS, USGS and USFS

Around this same time, the California USGS, NRCS and USFS had agreed to work together, and follow the Draft NRCS NI-170-304. In November 1995, these Calif. representatives of USGS and USFS drafted a letter to Paul Johnson (Chief of NRCS), from Jack Ward Thomas (Chief of USFS) and Mike Dombeck (Administrator Bureau of Land Management) with comments to the NRCS about these standards -- some of which were adopted in the current update to the NI, some of which were not. Most of these suggestions are now included in the draft FGDC hydrologic mapping standards (web site listed above).

The California Interagency Watershed Mapping Committee

In late 1995 the NRCS decided we would make better progress if we joined an Interagency Hydrologic Mapping Committee (IWMC) effort (State and Federal) here in California with a dataset that came to be known as CalWater. The USFS, USGS and NRCS presented the IWMC group with the NI 170-304 standards, which were included in the CalWater mapping standards, and the three Federal agencies agreed to support this State and Federal interagency mapping effort. An MOU was drafted in March 1997, which is just now getting its final signature and being finalized. In the meantime, linework continued.

The CDF CalWater 1.1 Effort

Back in 1995 the only digital watershed dataset in the State belonged to CDF -- and contained a number of administrative reporting, or political, boundaries. While no one was happy with this, all agreed it was the only place to start because it was all there was. It was called CalWater 1.1 and was delineated down to 3,000-10,000 acre watersheds (For more information on CDF's effort to develop CalWater 1.1 contact Clay Brandow). The State numbering and naming system was entirely different from the Federal system, as were the sizes of the watersheds in its hierarchy.

The DWR CalWater 2.0/2.2 Effort

Later, the Department of Water Resources took over coordination of the CalWater effort, resulting in versions 2.0 and 2.2 (For more information on DWR's effort contact Dick Neal). The State naming and numbering system has been retained in the current version (CalWater 2.2). By agreement of the IWMC, detailed watershed linework has focused on Northern and Central California, with only larger watershed units defined for Southern California. Much of the digitizing work has been contracted by various agencies on the committee to the Teale Data Center and overseen by Andy Richardson.

The Federal 8 digit HUCs were included in the CalWater dataset, and improvements made (that California USGS approved) on the 8 digit line work at the 1:24,000 level. However, there are places where the State and Federal system do not line up compatibly -- these are mentioned in the metadata, and a cross-walk was created (for more information on the crosswalk contact Paul Veisze of California Department of Fish and Game). For example, in some places 2-3 CU's correspond with one in the State system -- especially in Southern California.

The NRCS/USFS CalWater 2.5 Effort

The USGS 8 digit HUCs can be displayed from the CalWater linework, however, the sub watersheds below that level follow the state system of numbers and naming. No attempt has yet been made to aggregate these smallest units of CalWater to fit the definitions of the 11 and 14 digit sub watersheds and label them according to the Federal system. A visual assessment of the NRCS 11-digit blue-line map, with the CalWater smallest sub watershed linework shows that this should be possible.

The National Forest 5th-Field Maps

Parallel to this Interagency Effort (also 1995 to present), the Pacific Southwest Region of the Forest Service had its own mandates to move on with what they call the 5th-field sub watershed mapping (For more information on the USFS effort contact John Rector). The USFS 5th field watersheds are 10 digit codes, the 8 digit HUCs, plus 2 digits -- basically equivalent to what NRCS calls the 11-digit watershed level. They have proceeded to delineate, digitize and label these 5th field watersheds for the National Forest areas of California, following the Federal numbering system and NI-170-304 standards. Under a USFS contract with the Teale Data Center, some of this linework is incorporated in the current version of CalWater, while others are still being verified.

While the USFS numbering system for the 5th field is two digit, the numbering convention is the same. For NRCS use, when these are added to the CalWater dataset, an extra field can be added to the attribute table for the NRCS 11-digit version of this number system, using the USFS 2 digit codes with a following zero.

5th-Field 2 digit (01) vs. 3 digit (010)

This 3 digit vs. 2 digit sub watershed numbering debate adds to the confusion in the Interagency mapping. All Federal agencies (led by USGS and USFS) have agreed to continue the two digit numbering the USGS began with the 8 digit hydrologic unit mapping. Only NRCS is holding out for a 3 digit system (11 and 14 digit codes). Apparently, the FGDC guidelines for hydrologic mapping will set the 2 digit as a standard.  In California we have agreed to follow the 2 digit convention, and add an NRCS numbering field that is three digits, with the third digit being the following zero, so that we can have our maps certified under the current NRCS standard.

The Valley Lines

Another issue in our mapping effort is the large agricultural Central Valley. Original drainage patterns have long since be lost by water diversions and other structures. A sub-committee of the IWMC debated this issue, and decided to go with the California Department of Water Resources Drainage Analysis Units (DAU) linework. While these are not ideal, they are the best there is. NRCS currently has a $10,000 contract with the Teale Data Center to incorporate this linework, and final verification of the USFS 5th-field watersheds, into CalWater version 2.5. This approach complies with the NI-170-304 for flat terrain, agricultural areas.

During the development of the Watershed Boundary Dataset (WBD) in the CalWater watershed delineation workshops, it was decided to revisit the 4th level 8-digit boundaries in the Central Valley, and extend them fully into the valley.  Continuing delineation to the 5th and 6th level will depend upon the need and ability of these watersheds in meeting FGDC standards.

Populating CalWater with Federal Numbers

Finally, after a visual assessment of that 1978 11 digit sub watershed map, and the current CalWater 2.2 data, the 11 digit watersheds as delineated by hand appear to be identifiable within the CalWater watershed detail. To finalize these watersheds for NRCS purposes, it would require identifying and aggregating the smallest watershed units needed to match or approximate these 11 digit boundaries, and then adding the label fields in ArcView or ARC/INFO. There is enough sub watershed detail in CalWater (down to 3,000-10,000 acre watersheds) to define even the 6th field, what NRCS calls 14 digit (and USFS calls 12 digit) watersheds. After such an exercise in aggregating and labeling, a local verification of the linework would be needed at 1:24,000 scale. This exercise might also assist the CalWater IWMC effort in delineating watersheds in Southern California.

Today

The effort continues in each state to delineate and digitize these two levels (5th and 6th), and is handled through the NRCS state offices in partnership with local and state agencies, other federal agencies, and others interested in the effort. A list of NRCS state contacts and mapping progress in each state, and examples of different State efforts are available online.

NRCS Hydrologic Unit Mapping in California

In the NRCS California State office, work on the hydrologic unit mapping has been shared between the Natural Resources Inventory section, and Watershed Planning Services (until 1998 known as Water Resources Planning). However, there is a long history of interagency cooperation with other State and Federal agencies, primarily through the California State Interagency Watershed Mapping Committee (IWMC).

Status of California NRCS Mandated HU mapping effort:

(Report to Kenny Legleiter, NRCS Fort Worth, Texas, on Status of HU Mapping, February 2000)

  1. Most of the state of California has been digitized in an Interagency Watershed Mapping Committee (IWMC) effort resulting in a dataset called CalWater (see summaries by CERES and CDF). These data are generally more detailed than what NRCS would call the 11 and 14 digit level (the interagency CalWater dataset has digitized watersheds down to 3,000-10,000 acres).

    Mapping Standards

    In terms of the 1992 NRCS mapping standard, the watershed linework is questionable in many places, given its origin with a state agency (CDF) that originally used different standards (i.e. some boundaries in the State hierarchy are administrative reporting units). However, the IWMC agreed to follow the USGS and NRCS mapping standards as the primary guideline (hopefully soon to be updated with an FGDC interagency guideline), which with further editing and validation, should eventually bring these lines into compliance. However, there are no immediate plans to do this.

  2. We are just beginning to contact our neighboring states (Oregon, Nevada and Arizona) to check the boundaries of the sub watersheds to make sure they match.

  3. Metadata is complete that minimally meets FGDC standards. However, the wording of the existing metadata is still awaiting review by the IWMC (there are some misleading statements in it about the boundaries being administrative reporting units vs. actual hydrologic drainages). No attempt has been made to add further detail to the metadata.

  4. Information about the NRCS effort can be found at the NCGC (National Cartographic and Geospatial Center) of the NRCS in Fort Worth. The NRCS online status database says we have delineated the entire state (hand delineated on paper back in 1978). We have digitized to a finer sub-watershed level than the NRCS 14-digit in the CalWater linework. See the more detailed explanation below in the History.

There is a long history of NRCS involvement with the Interagency Watershed Mapping Committee and the CalWater dataset. More information on CalWater can be found at the California Spatial Information Library. For help in understanding the CalWater attributes, and the relationships between the State and Federal naming and number systems, visit the CalWater FAQ.



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