In general terms, a hydrologic unit can be defined as any geographic area where all water within that area naturally drains to a specific outlet or pour point. To better classify hydrologic units they are commonly divided into size classifications called “Fields”. “Fields” define drainage areas of specific size within a network of hydrologic units. The largest classification of this kind is termed a 1^st Field watershed (also called a Region). One example of a 1^st Field watershed is the Columbia River Basin Region, which defines the drainage network for the majority of the States of Oregon and Washington. As part of the ranking system, 1^st Fields break down into smaller 2^nd Fields which can then be further subdivided into 3^rd Fields and so on. These divisions may continue until much smaller 8^th Fields are reached. Delineation of these divisions is based on the Interagency Guidelines on Delineation of Watershed and Subwatershed Hydrologic Unit Boundaries (http://wwwga.usgs.gov/gis/iag.html).

The purpose of the hydrologic unit boundary dataset is to simultaneously create a complete index of hydrologic unit boundaries representing the boundaries for 1^st through 8^th Field hydrologic units. This dataset was built to allow users the ability to query hydrologic units as whole polygons or as individual arcs, based on certain historical information. The attribute descriptions contained in this document explain the information that is available in this dataset and how users are to interpret that information.

File Naming Convention

After much discussion about what to name this new hydrologic boundary dataset, the core OGIC Hydro group decided that that dataset should be named “PNW_HUCvXX”. What does this mean? This new coverage name stands for Pacific Northwest Hydrologic Unit Codes, version <some_number>. The “XX” represents the current “version” number of the coverage. By “versioning” this coverage, users of the data have an easy way to track the coverage and a quickly look for recent updates to their version. This will allow more people to be working with the same, and most recent, dataset. The names of the coverage will actually be named “PNW_HUCv1”, “PNW_HUCv2”, “PNW_HUCv3”, etc. as the versioning process continues.

Attributing Standards

When inputting information into database items, all attributes will be added in ALL UPPERCASE format. This will allow for consistency in database management and querying.

Attributes for Polygons (PAT)

Because hydrologic units are divided into different size categories, each “Field” receives its own two-digit, numeric identification code. The combination of these numeric codes creates a unique identifier for each subdivision. The approach to defining the unit identification code is discussed in detail later in this document.

1. Acres - (Required)

Note: This item is based on the national interagency protocol.

This attribute is to be calculated from the internal “Area” attribute.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

ACRES 12 12 N 4 26739.2359

2. Hydrologic Unit “Field” Codes - (Required)

As required by the national protocols, hydrologic units of the same “Field” type (for example, all 6^th field hydrologic units within a 5^th field) must be sequentially numbered, starting from the most upstream unit and progressing downstream.

The structure of this attribute allows each subdivision to be queried by their full or partial hydrologic unit number. Where a specific hydrologic unit has not yet been delineated, the attribute value “XX” shall serve as a placeholder instead of the standard numeric code.

1^st 2^nd 3^rd 4^th 5^th 6^th 7^th 8^th

17 | 10 | 02 | 03 | 02 | 09 | 02 | XX

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

HUC_NUM 16 16 C - 17100203020902XX

Example Explanation: When delineating 7^th field sub-watersheds, all 7^th fields within the same 6^th field will have the same first 12 digits. Starting at the uppermost end of the drainage, the first 7^th field hydrologic unit would be assigned the code “01” for the 13^th and 14^th digits. When combined with the 6^th field code, the full Hydrologic Unit Code in the above example would be 17100203020901XX. The next downstream hydrologic unit would be assigned the code “02” for its 13^th and 14^th digits, making its full HUC code be 17100203020902XX and so on. The “XX” at the end of the example tells users that 8^th field watersheds have not yet been delineated in this area. This coding scheme should be applied when delineating hydrologic units anywhere from 5^th through 8^th fields.

3. Hydrologic Unit Types - (Optional)

Based on the need to determine how hydrologic units were defined, the “hydrologic unit type” class was formed. This attribute allows users to query hydrologic units by composition type based on its delineation method. Information is presented as a running string, similar to the numeric “field” codes. Individual characters of the string represent the formation characteristics for each hydrologic unit level. Where a hydrologic unit level has not been delineated or the type has yet to be classified, an “X” will be used as a placeholder. This is an optional attribute that may be populated for 1^st through 8^th field hydrologic units where necessary.

1^st 2^nd 3^rd 4^th 5^th 6^th 7^th 8^th

T | T | T | T | T | T | C | X

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

HUC_TYPE 8 8 C - TTTTTTCX

Standard values currently include the following:

T “True”, “pure”, or “classic” hydrologic units are land areas having all the surface drainage within its boundary converging at a single point.

C “Composite” hydrologic units, or “remnant areas” are drainage areas typically formed as the residual areas after delineation of classic watersheds. The most common example of a remnant area is the small triangular wedge between the boundaries of adjacent hydrologic units flowing into the same side of another stream.

F “Frontal” hydrologic units are areas that include multiple, non-convergent rivers. Frontal units would most likely be related to hydrologic units feeding into the Pacific Ocean or Columbia River.

X Unclassified hydrologic units

4. Hydrologic Unit Naming Protocol - (Required)

The following attribute items are intended for officially recognized names only. The hydrologic unit name and hydrologic unit “Field” code attributes relate in the following ways:

1^st Field = Region

2^nd Field = Sub-Region

3^rd Field = Basin

4^th Field = Sub-Basin

5^th Field = Watershed

6^th Field = Sub-Watershed

7^th Field = Catchment

8^th Field = Sub-Catchment

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLES

REGION_NAME 30 30 C - PACIFIC NORTHWEST

SUBREGION_NAME 30 30 C - OREGON/WASHINGTON COASTAL

BASIN_NAME 30 30 C - NORTHERN OREGON COASTAL

SUBBASIN_NAME 30 30 C - ALSEA

WATERSHED_NAME 80 80 C - UPPER ALSEA RIVER

SUBWAT_NAME 80 80 C - UPPER NORTH FORK ALSEA RIVER

CATCHMENT_NAME 80 80 C - RACKS CREEK

SUBCATCH_NAME 80 80 C -

The following guidelines should be used when assigning a name to a hydrologic unit polygon:

1. Assign each hydrologic unit with a unique name relating to a major hydrologic feature within the hydrologic unit.

2. If primary water features in different hydrologic units have the same name, use the primary water feature for each hydrologic unit modified by appending the name of the receiving water body. For example: “DRIFT CREEK/SILETZ RIVER” or “DRIFT CREEK/MCKENZIE RIVER”.

3. It is appropriate to use streams, lakes, and reservoirs as major hydrologic features for naming. Preference should be given to streams unless the polygon contains a dominant lake or reservoir. Example: “HARNEY LAKE/MALHEUR LAKE”.

4. Use main stem stream names at the outlet of the hydrologic unit whenever possible.

5. End each hydrologic unit name with one of the following words spelled out in entirety: "RIVER", "CREEK", "BRANCH", "FORK", "SLOUGH", "LAKE", "BAY", "FRONTAL", "RESEVOIR", "INLET", "CHANNEL", "HARBOR", "COVE", "HEADWATERS", "SEA", "OCEAN", "BAYOU", and "ESTUARY".

6. Avoid abbreviations, e.g., “N. FK.”, “R.”, “RES.”, etc.

7. When a major river is subdivided into multiple hydrologic units along the main stem length, the preferred naming convention is "UPPER", "MIDDLE", or "LOWER".

8. If a main stem river is subdivided into more than three hydrologic units, do not use the "UPPER", "MIDDLE" and "LOWER" naming convention. Use the standard naming protocol. If the name includes the name of a primary tributary or primary hydrologic feature, separate the names with a "forward slash (/)" character; e.g., “UPPER WILLAMETTE RIVER/DEEP CREEK”.

9. Use of the word “OF” is appropriate to shorten the naming convention of tributaries sharing the same name of the main stem river, e.g., “NORTH FORK OF THE WILLAMETTE RIVER”, “UPPER NORTH FORK OF THE COAST FORK OF THE WILLAMETTE RIVER”.

10. Use of the term “FRONTAL” is reserved for areas that include multiple, non-convergent rivers. The sequence for naming areas in the Frontal should follow from north to south; e.g., “NETARTS BAY/SAND LAKE/NESKOWIN CREEK”.

11. Name attributes should only be assigned for hydrologic units that have been delineated.

12. For organizations who desire to use locally recognized names in association with a particular hydrologic unit(s), the suggested method is to use a relate table based upon the Hydrologic Unit Code numbers.

5. Historical Hydrologic Unit Number - (Required)

Because of the national protocol requirement for sequential downstream numbering within hydrologic units, there may be instances where the new hydrologic unit numbers may not be consistent with some historical hydrologic unit numbers. With the renumbering of the hydrologic units, a link may be needed to assist users in identifying hydrologic units based on the historical hydrologic unit numbers.

This attribute should contain the historical hydrologic unit numbers that were assigned prior to the renumbering process.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

OLD_HUCNUM 16 16 C - 1710020309XXXXXX

6. States - (Required)

Note: This item is based on the national interagency protocol.

This attribute should include the names of all states that a particular hydrologic unit falls within. Use the 2-digit postal code abbreviation and sort the states in alphabetical order, with a hyphen separating each state.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

STATES 12 12 C - ID-OR-WA

Example Explanation: ID-OR-WA represents a hydrologic unit that overlaps the Idaho, Oregon, and Washington borders.

7. Non-Contributing Areas - (Required)

Note: This item is based on the national interagency protocol.

Drainage areas that do not flow toward the outlet of any hydrologic unit are considered non-contributing areas. Such areas may be due to glaciated plains (potholes), enclosed basins, karst topography, playas, cirques, depression lakes, dry lakebeds, or similar landforms. Such areas may be large enough to be designated as a sub-division unto itself. The largest non-contributing area in the U.S. is the area of the Great Basin in Utah. This closed area is large enough to be considered as a sub-region hydrologic unit.

If non-contributing areas are relatively small, or if they are scattered throughout a drainage area, they should be considered as part of the delineated hydrologic unit. Record the acreage of non-contributing area for the hydrologic unit down to the smallest mapped hydrologic unit “Field” in the given subdivision.

If a non-contributing area is on the boundary between two or more hydrologic units, determine the low point along the non-contributing area boundary. The hydrologic unit adjacent to the low point on the boundary should be associated with this non-contributing area. Occasionally, a non-contributing area may be drained (via canal or pipeline), thus becoming part of a surrounding or adjacent hydrologic unit. Local investigation in cases of suspected drainage or diversion might be needed.

Document the criteria used to delineate non-contributing areas in the metadata file if a significant number of non-contributing areas are defined. Include the amount of non-contributing areas within a hydrologic unit as an attribute of the database. Delineate non-contributing areas in a consistent manner throughout the state.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

NCONTRIB_DA* 12 12 N 4 325.9362

*Based on the Federal Interagency Standards, this item definition is 4,4,B. It was recommended we expand the NCONTRIB_DA item definition to allow a higher level of accuracy.

8. Fifth Field Down Stream Hydrologic Unit - (Required)

Note: This item is based on the national interagency protocol.

This field represents the hydrologic unit (of the same level) receiving the majority of the downstream flow. Outlets created by ditching or other artificial drainage are not to be considered for this field. Where a specific fifth field hydrologic unit has not yet been delineated, the attribute value “XX” shall serve as a placeholder instead of the standard numeric code.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

DS_HUC5 10 10 C - 1710020504

9. Sixth Field Down Stream Hydrologic Unit - (Required)

Note: This item is based on the national interagency protocol.

This field represents the hydrologic unit (of the same level) receiving the majority of the downstream flow. Outlets created by ditching or other artificial drainage are not to be considered for this field. Where a specific sixth field hydrologic unit has not yet been delineated, the attribute value “XX” shall serve as a placeholder instead of the standard numeric code.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

DS_HUC6 12 12 C - 171002050403

10. Hydrologic Unit Modifications - (Required)

Note: This item is based on the national interagency protocol. This attribute item directly relates to the attribute item called FLAGS in the national protocol. The item name “FLAGS” was deemed unacceptable based on discussions with the core OGIC Hydro group because it does not imply any intuitive meaning. Therefore the item name FLAGS was replaced with the name Hydrologic Unit Modifications (or HUC_MOD) name.

This attribute should contain information unique to the hydrologic unit sub-division for a particular record. This may include information on the type of structure, date of construction or other features that may influence surface water flow.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

HUC_MOD 80 80 C - CANAL

Example Explanation: Possible examples include canal, ditch, control structure, diversion, etc.

11. Comment - (Optional)

This attribute may include any additional information that pertains to the hydrologic unit’s polygon history or general characteristics that cannot be adequately described in previous items.

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLE

COMMENT 100 100 C - WALDO LAKE

Example Explanation: On a map, the feature containing the value shown above represents Waldo Lake.

Polygon Attribute Table (PAT)

HIGHLIGHTED = From the “Federal Interagency Standards…” protocol

ITEM NAME WIDTH OUTPUT TYPE N.DEC EXAMPLES

ACRES 12 12 N 4 2187.4971

HUC_NUM 16 16 C - 171002030902XX

HUC_TYPE 8 8 C - TTTTTCX

REGION_NAME 30 30 C - PACIFIC NORTHWEST

SUBREGION_NAME 30 30 C - OREGON-WASHINGTON COASTAL

BASIN_NAME 30 30 C - NORTHERN OREGON COASTAL

SUBBASIN_NAME 30 30 C - ALSEA

WATERSHED_NAME 80 80 C - UPPER ALSEA RIVER

SUBWAT_NAME 80 80 C - UPPER NORTH FORK ALSEA RIVER

CATCHMENT_NAME 80 80 C - RACKS CREEK

SUBCATCH_NAME 80