In cooperation with the Texas Natural Resource Conservation Commission Creating a Standardized Watersheds Database for the Lower Rio Grande/ Río Bravo, Texas Open-File Report 00–065 TEXAS U.S. Department of the Interior U.S. Geological Survey Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 2. REPORT TYPE 3. DATES COVERED 2000 N/A - 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Creating a Standardized Watersheds Database for the Lower Rio 5b. GRANT NUMBER Grande/Rio Bravo, Texas 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION U.S. Department of the Interior 1849 C Street, NW Washington, DC REPORT NUMBER 20240 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF ABSTRACT OF PAGES RESPONSIBLE PERSON a. REPORT b. ABSTRACT c. THIS PAGE SAR 21 unclassified unclassified unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 U.S. Department of the Interior U.S. Geological Survey Creating a Standardized Watersheds Database for the Lower Rio Grande/ Río Bravo, Texas By Julie R. Brown, Randy L. Ulery, and Jean W. Parcher U.S. GEOLOGICAL SURVEY Open-File Report 00–065 In cooperation with the Texas Natural Resource Conservation Commission Austin, Texas 2000 U.S. DEPARTMENT OF THE INTERIOR Bruce Babbitt, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information write to District Chief U.S. Geological Survey 8027 Exchange Dr. Austin, TX 78754–4733 E-mail: [email protected] Copies of this report can be purchased from U.S. Geological Survey Branch of Information Services Box 25286 Denver, CO 80225–0286 E-mail: [email protected] CONTENTS Abstract ............................................................................................................................................................... 1 Introduction ......................................................................................................................................................... 1 Purpose and Scope ................................................................................................................................... 2 Acknowledgments .................................................................................................................................... 2 Background .............................................................................................................................................. 3 Watershed-Boundary Delineation .................................................................................................. 3 Standardized Watershed Classification .......................................................................................... 4 Watershed Characteristics .............................................................................................................. 5 Topographic Datasets ..................................................................................................................... 5 Methods Used to Create a Standardized Watersheds Database .......................................................................... 5 Source Datasets ........................................................................................................................................ 5 DEM Processing—Creation of Hydrologic Derivatives .......................................................................... 6 Watershed Delineation ............................................................................................................................. 8 Revision of the Hydrography ......................................................................................................... 8 Computer-Generated Watershed Delineations ............................................................................... 9 Review of Computer-Generated Watershed Delineations and Manual Delineations .................... 10 Watershed Region Coverage .......................................................................................................... 10 Watershed Characteristics ........................................................................................................................ 10 Conflation of RF3 Attributes .................................................................................................................... 10 Extending Hydrologic Unit Code (HUC) to 12 Digits ............................................................................. 12 Conclusions ......................................................................................................................................................... 12 Selected References ............................................................................................................................................ 13 Appendix—Watershed Characteristic Computations ......................................................................................... 15 FIGURES 1. Map showing location of study area ..................................................................................................... 3 2–4. Diagrams showing: 2. Flow-direction grid ..................................................................................................................... 7 3. Flow-accumulation grid............................................................................................................... 8 4. Stream network derived from flow-accumulation grid ............................................................... 9 TABLE 1. Watershed characteristics or classification codes ................................................................................. 11 ACRONYMS AML -Arc Macro Language NED - National Elevation Database CIR - Color infrared NHD - National Hydrography Dataset CRP - Clean Rivers Program NMD - National Mapping Division DEM - Digital elevation model NRCS - Natural Resources Conservation Service DLG - Digital line graph NSDI - National Spatial Data Infrastructure DOQ - Digital orthophoto quadrangle NWIS - National Water Information System EPA - U.S. Environmental Protection Agency OMB - Office of Management and Budget ESRI - Environmental Systems Research Institute RF3 - River Reach File version 3.0 FGDC - Federal Geographic Data Committee STORET - STOrage and RETrieval HUC - Hydrologic Unit Code TNRCC - Texas Natural Resource Conservation Commission NAWQA - National Water-Quality Assessment USGS - U.S. Geological Survey CONTENTS iii Creating a Standardized Watersheds Database for the Lower Rio Grande/ Río Bravo, Texas By Julie R. Brown, Randy L. Ulery, and Jean W. Parcher Abstract orthophoto quadrangle. Computer-generated, standardized watersheds that are vertically inte- This report describes the creation of a large- grated with existing digital line graph hydrographic scale watershed database for the lower Rio Grande/ data will continue to be difficult to create until revi- Río Bravo Basin in Texas. The watershed database sions can be made to existing source datasets. Until includes watersheds delineated to all 1:24,000- such time, manual editing will be necessary to scale mapped stream confluences and other hydro- logically significant points, selected watershed make adjustments for man-made features and characteristics, and hydrologic derivative datasets. changes in the natural landscape that are not reflected in the digital elevation model data. Computer technology allows generation of preliminary watershed boundaries in a fraction of the time needed for manual methods. This auto- INTRODUCTION mated process reduces development time and results in quality improvements in watershed Watersheds are natural boundaries dividing the boundaries and characteristics. These data can then land into water-resource management units that often be compiled in a permanent database, eliminating are more useful than other traditional boundaries (for the time-consuming step of data creation at the example, political boundaries). Issues such as water beginning of a project and providing a stable base quality, water allocation, drought, and flood manage- dataset that can give users greater confidence when ment, as well as aquatic habitat protection and manage- further subdividing watersheds. ment all depend on watershed-level data, and watershed A standardized dataset of watershed charac- boundaries frequently are used in studies dealing with teristics is a valuable contribution to the under- these types of issues. Therefore, it is becoming increas- standing and management of natural resources. ingly desirable to have a comprehensive, standardized, Vertical integration of the input datasets used to large-scale watershed database for a State and for the automatically generate watershed boundaries is Nation. Such a database would avoid duplication of crucial to the success of such an effort. The opti- data, and further subdelineation of watersheds would be mum situation would be to use the digital ortho- more consistent with existing watershed boundaries. photo quadrangles as the source of all the input The following programs demonstrate the need for a datasets. While the hydrographic data from the dig- large-scale watershed database: ital line graphs can be revised to match the digital orthophoto quadrangles, hypsography data cannot (cid:127) The U.S. Environmental Protection be revised to match the digital orthophoto quadran- Agency (EPA) currently emphasizes gles. Revised hydrography from the digital ortho- a watershed-management approach photo quadrangle should be used to create an to integrated development, imple- updated digital elevation model that incorporates mentation, and enforcement of water- the stream channels as revised from the digital quality protection programs. Abstract 1 (cid:127) The Natural Resources Conservation ences and other hydrologically significant points, Service (NRCS), U.S. Department of selected watershed characteristics, and hydrologic Agriculture, conducts its agricultural derivative datasets. support programs for small water- shed planning and engineering within Purpose and Scope a watershed framework. The purpose of this report is to: (cid:127) The Texas Natural Resource Conser- vation Commission (TNRCC), as (cid:127) Describe an automated procedure for the preliminary part of its Basin Planning initiative, delineation of 1:24,000-scale watersheds using emphasizes a watershed-based USGS digital elevation and hydrographic data as approach to the assessment, manage- well as Environmental Systems Research Insti- ment, and protection of river basin tute (ESRI) Arc/Info GRID software. water quality in Texas (Texas Natural (cid:127) Describe the technical review process needed before Resource Conservation Commission, the preliminary delineations can be considered 1994). TNRCC has previously sup- representative of the watershed. This includes ported development of watershed comparison of the 1:24,000-scale digital line boundaries and attributes by the U.S. graph (DLG) hydrography to current digital Geological Survey (USGS) at USGS orthophoto quadrangles (DOQs) and revision of and Clean Rivers Program (CRP) these data as needed. water-quality sampling sites across the State (Tan, 1997). (cid:127) Describe the attribution of the final watersheds with standard watershed characteristics as recom- (cid:127) Watershed boundaries are a base mended in the “National Handbook of Recom- data layer for the USGS National mended Methods for Water-Data Acquisition” Water-Quality Assessment (U.S. Geological Survey, 1978). (NAWQA) Program, a national study encompassing most of the major river (cid:127) Describe the conflation of the 1:100,000-scale River basins or aquifers in the United Reach File version 3.0 (RF3) dataset attributes to States. Knowledge of the characteris- 1:24,000-scale DLG hydrography. tics of the watershed above a sam- pling site on a stream is critical to a (cid:127) Describe the limitations, lessons learned, and bene- major NAWQA program goal of fits of using an automated process to develop dig- establishing cause and effect relations itally based, large-scale watershed delineations. Creating a Standardized for point- and non-point source The geographic scope of this study included an water-quality contaminants. Watersheds Database area of about 2,000 square miles in the lower Rio NAWQA studies in Texas are making Grande/Río Bravo Basin in Texas, consisting of Hydro- extensive use of watershed bound- for the Lower Rio logic Unit Code (HUC) 13090001, HUC 13090002, and aries and characteristics. the Arroyo Colorado Basin within HUC 12110208 Grande/Río Bravo, Numerous other local, State, and Federal agen- (fig.1). cies, ranging from municipal flood-control districts and Texas Digital datasets created in this study are available river authorities to the U.S. Army Corps of Engineers, over the Internet at http://pubs.water.usgs.gov/ implement their water-resources and environmental- ofr00065. protection programs within a watershed framework. During 1998–99 a large-scale watershed database Acknowledgments was created for the lower Rio Grande/Río Bravo Basin in Texas by the U.S. Geological Survey, in cooperation The authors wish to thank Dana Barbie and with the Texas Natural Resource Conservation Com- Tim Raines, USGS hydrologists, and Roger Miranda, mission. The watershed database includes watersheds TNRCC, who evaluated the computer-generated, delineated to all 1:24,000-scale mapped stream conflu- preliminary watershed boundaries. 2 Creating a Standardized Watersheds Database for the Lower Rio Grande/Río Bravo, Texas 99o 98o30' 98o 97o30' HUC 13090001 26o30' HUC 12110208 RI O RI O BRAVO Arroyo Colorado Basin MEXICO GRANDE HUC 13090002 26o 0 10 20 30 40 MILES G UMLEFX IOCFO TEXAS Study area LOCATION MAP Figure 1. Location of study area. Background watershed adequately represents the actual watershed. In addition to topographic information and hydrogra- Watershed-Boundary Delineation phy, ancillary information such as location of roads, bridges, diversions, and impoundments are required to Historically, watershed-boundary delineation and delineate and map watershed boundaries accurately. mapping has been a labor-intensive activity requiring access to an extensive topographic map library and to The development of watershed boundaries from ancillary maps and documents. The delineation process digital sources using computer software removes much requires a visual interpretation of features on the map of the subjective nature of the delineated boundary and, therefore, is somewhat subjective, relying on because others using the same datasets can reproduce hydrologic judgement to ensure that the delineated the same watershed boundary. Using a computer, the INTRODUCTION 3 analyst can delineate watershed boundaries in a fraction uniquely identified by an 8-digit numeric code. of the time needed for traditional hand methods. How- Intended primarily as a planning tool, the boundaries ever, an experienced hydrologist should review the of the HUC coding system divide the country into 21 boundaries, and adjustments might be necessary to regions, 222 sub-regions, 352 accounting units, and account for man-made features/alterations or other con- 2,149 cataloging units. A HUC includes the contribut- ditions that are not reflected in the digital elevation ing drainage to a hydrologically significant point on the model (DEM). The final product optimizes the effi- stream. Hydrologically significant points include the ciency of the computer with the judgement of a hydrol- mouths of major river basins, the reach of a river and the ogist to produce a high-quality delineation of the tributaries to that reach, a group of streams forming a watershed or parts of watersheds. coastal drainage area, or a distinct hydrologic feature (for example a major dam or stream confluence). A set Many organizations have needed watershed of State Hydrologic Unit maps (1:500,000-scale) pub- boundaries but have not had the resources to create them on a national scale. Watersheds have been delineated by lished by the USGS in 1974 depicted the HUC bound- various agencies for their particular application or aries. These HUC maps were subsequently modified to project, using various source and scale maps. For many create the most comprehensive, digital watershed- boundary data layer available on a statewide basis years the USGS, as part of its mission to provide stream- (Seaber and others, 1987). This is the only existing stan- flow and water-quality information, has delineated dardized watershed-boundary dataset that extends selected watersheds on paper topographic maps to determine basin characteristics associated with gaging across state boundaries to encompass all river basins in stations or monitoring sites. State and local agencies the United States; however, use of the HUC maps is lim- typically prepare maps and reports that contain water- ited to State, regional, or national applications because of the 1:250,000 scale. shed boundaries for their particular geographic region HUCs are an accepted national framework for of interest. In a few states, the USGS has worked closely water- and land-resource planning in many states, as with its cooperators at the regional level, particularly in coastal areas of low relief, to delineate large-scale well as in the Federal government. The major Federal watersheds. Information gathered from large-scale water-quality databases (STORET and NWIS) are maps is extremely important in the construction of attributed with the HUCs to catalogue and access water- quality data. Currently (1999), cooperative National watershed boundaries. In these states with USGS input, Spatial Data Infrastructure (NSDI) framework develop- the watershed delineations, after thorough review by all ment efforts by the USGS and EPA involve the produc- interested parties, typically have become the “official” watershed boundaries for the state (Ellis and Price, tion of a National Hydrography Dataset (NHD) at the 1995). 1:100,000 scale that incorporates the HUC as part of a unique feature identification number assigned to river segments. Standardized Watershed Classification Although useful for regional and national plan- The USGS, under provisions of the Office of ning, the 8-digit HUC does not provide sufficient detail Management and Budget (OMB) (Darman, 1991), has to uniquely identify subsequent larger-scale watersheds. Federal leadership responsibility for overall water-data Various methods have been proposed to extend the HUC coordination including custody of the national hydro- to 10 digits and then to 12 digits (watershed and sub- logic unit maps and development of the HUC system in watershed levels). In recent years the NRCS has led cooperation with the U.S. Water Resources Council. efforts to extend the 8-digit HUC code to an 11-digit This system defines an 8-digit standardized coding code and then a 14-digit code (U.S. Department of Agri- scheme that serves as a base for the cataloging, index- culture, 1995). The NRCS also has promoted the devel- ing, and referencing of hydrologic data (U.S. Geologi- opment of watershed and sub-watershed mapping and cal Survey, 1982). The system divides the United digitizing by doing some delineation of 11-digit HUCs. States into a 4-level hierarchy of regions, sub-regions, Some NRCS State offices have been working on 14- accounting units, and cataloging-unit-sized drainage digit HUC delineation. The USGS currently (1999) is areas. Each level of the hierarchy is assigned a 2-digit working with other Federal agencies to draft a Federal code. The 2-digit codes can be linked together to yield a Geographic Data Committee (FGDC) Thematic Stan- unique identifier, therefore each cataloging unit is dard for watershed mapping, delineation, digitalization, 4 Creating a Standardized Watersheds Database for the Lower Rio Grande/Río Bravo, Texas and attribution (Robert Pierce, U.S. Geological Survey, Topographic Datasets written commun., 1997). This effort will support a Topographic datasets such as flow direction and nationally consistent method for digital watershed flow accumulation (also referred to as hydrologic deriv- mapping and attribution in the United States and, if ative datasets) often are constructed as needed and are adopted, will afford the recognition of watershed used as source datasets for the watershed-delineation boundaries as a national framework dataset that is part process. Each topographic dataset may take several of the NSDI (Federal Geographic Data Committee, hours of computer time to produce, the datasets then are written commun., 1996). discarded because of limitations of computer storage. Use of the interim topographic datasets from this report Watershed Characteristics eliminates the need for end users of the database to reproduce the datasets. Subdivision of an existing Delineation of the watershed boundary is typi- watershed using a publicly available interim dataset cally an initial step in the study and management of would yield a sub-watershed with boundaries that water resources. As many as 27 key watershed match the existing standardized watershed delineations, characteristics might be required during routine water- stream segments, and basin characteristics. By using the resource investigations. The following selected mor- same source datasets, end users would avoid common phometric watershed characteristics are necessary problems of edge matching with adjacent watersheds. A attributes for many water-resource investigations: con- long-term benefit is that these base topographic tributing drainage area, average slope, maximum and datasets, used in conjunction with the standardized minimum elevation, drainage density, and basin length watershed boundaries, make possible an interactive and width. Many additional watershed or streamflow watershed subdelineation capability useful to on-line or characteristics could be derived from these attributes. Internet-based resource management and assessment Selected flow characteristics of the stream can be systems. reasonably estimated from watershed characteristics METHODS USED TO CREATE A using statistical techniques. Many watershed hydrologic models require a set of basin characteristics as input STANDARDIZED WATERSHEDS variables. Ecological studies and aquatic habitat assess- DATABASE ments frequently need basin characteristics; however, these applications typically involve large-scale datasets Source Datasets and large-scale watershed delineations that often are Three standard USGS National Mapping Divi- unavailable. sion (NMD) products were used for the watershed- In the past, determination of watershed character- delineation study. These included 3.75-minute DOQs, istics has been a labor intensive, time consuming pro- 7.5-minute DLG hydrography vector data, and a version cess that is subject to error; the reproducibility of these of the National Elevation Database (NED). The NED is data also is problematic. With computer technology this a seamless “best available” DEM for the area. This NED process can be automated, resulting in a higher quality product, with the same resolution as the 7.5-minute product than previously attainable using hand methods. DEMs, reduced the amount of time needed to assemble This automated process has a major benefit in addition the elevation datasets for the study area. to reduced development time and quality improve- Each of the mapping products used in this study ments; the watershed boundaries and characteristics can was produced using source materials with different be pre-determined and placed in a permanent database. dates. For example, the aerial photographs used to cre- This eliminates the often time-consuming step of hav- ate the DOQs had a source date of 1995, whereas the ing to create a watershed database at the initiation of a topographic maps showing the hydrographic and hypso- project. An existing watershed database also provides a graphic data had earlier source dates from the 1970s and stable base dataset that affords users higher confidence 1980s. Vertical integration of input datasets used to when further subdividing watersheds. A standardized automatically generate watershed boundaries is crucial. dataset of watershed characteristics attributed to the Vertical integration between datasets cannot be assured watershed boundary is a valuable contribution to the if the source date of materials is different. Taking into understanding and management of natural resources. consideration the difference between the source dates is METHODS USED TO CREATE A STANDARDIZED WATERSHEDS DATABASE 5