2.2 Developing the schema of the Water Quality Data Model (WQDM)
A water quality framework is being created in Visio 2000 to have the Rio Grande Water Quality UML file. This framework follows the ArcHydro data Model philosophy, but some changes are being made to the attribute tables of the feature classes, in order to met criteria and parameters required by the TCEQ, EPA, USGS, IBWC, CILA, and CNA.
Once the Water Quality Data Model UML has been created, it must be exported as mdb file to create the schema, which will be applied to a relational geodatabase in ArcCatalog.
2.3 Spatial reference information
Projected Coordinate System: NAD_1983_Albers
Projection: Albers
False_Easting: 1000000.00000000
False_Northing: 1000000.00000000
Central_Meridian: -103.00000000
Standard_Parallel_1: 27.41666667
Standard_Parallel_2: 34.91666667
Latitude_Of_Origin: 31.16666667
Linear Unit: Meter (1.000000)
Geographic Coordinate System:
GCS_North_American_1983
Datum: D_North_American_1983
Prime Meridian: 0
2.4 Entity and attribute information
2.4.1 Feature Class: HydroEdge
This feature class depicts the official TCEQ Stream Segments for the State of Texas as listed in Title 30, Chapter 307 of the Texas Administrative Code (TAC), also known as the Surface Water Quality Standards on the US side, and the official CNA or SEMARNAT Stream Segments for the Mexican side of the Rio Grande/Bravo basin. These are streams and waterbodies that have been individually defined by the TCEQ and the other participating agencies and assigned unique identification numbers. Intended to have relatively homogeneous chemical, physical, and hydrological characteristics, a segment provides a basic unit for assigning site-specific standards and for applying water quality management programs of the agency. Both "classified" and "unclassified" segments have been included in this feature class. Classified segments, also referred to as designated segments, refer to water bodies that are protected by site- specific criteria. The classified segments are listed and described in Appendix A and C of Chapter 307.10 of the TAC. The site-specific uses and criteria are described in Appendix A. Classified waters include most rivers and their major tributaries, major reservoirs, and estuaries. Unclassified waters are those smaller water bodies that do not have site-specific water quality standards assigned to them, but instead are protected by general standards that apply to all surface waters in the state. This feature class also identifies which segments and water bodies have been listed as impaired or threatened in the final draft of the Texas 2000 Clean Water Act Section 303(d) List (effective August 31, 2000) for the U.S. side of the Rio Grande/Bravo basin. An impaired segment is a water body which does not meet the standards set for its use, or is expected not to meet its use in the near future. The impaired code table associated with this feature class contains fields which indicate which segments are impaired and which pollutants are responsible for the failure of those segments to meet water quality standards. The hydrography described as HydroEdges in the Rio Grande/Bravo basin geodatabase for the water quantity developed in the CRWR is used to define these river segments within the WQDM.
a. Attribute: HydroID. This is the unique 10 digit identification number assigned by the CRWR. This ID will be used to establish the topology in the geometric network. The HydroID for this element would be assigned as described below:
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The first digit indicates the country where the element is located. It was defined the number 1 for the segments located on the US side, and 2 for the segments located on the Mexican side. The next two digits indicate the hydrological subregions, 9 on the American side and seven on the Mexican side. The next two digits indicate the feature class within the geodatabase. Number 02 was assigned to HydroEdge feature class, which contains the river segments, and the last five digits describe the river segment number.
b. Attribute: HydroCode. This is the public identification number assigned by the TCEQ, USGS, EPA, IBWC, or CNA.
c. Attribute: ReachCode. This field is added to store the ReachFile from the EPA
d. Attribute: Name. The name of the classified or unclassified segment as it appears in the Texas Surface Water Quality Standards on the US side, and as it appears in the National Water Commission (CNA) or the Natural Resources and Environmental Secretary (SEMARNAT) classification on the Mexican side.
e. Attribute: LengthKm. This field indicates the river segment length in Km
f. Attribute: LengthDown. This field indicates the distance of the river segment to the outlet of the Rio Grande/Bravo basin, usually calculated in kilometers based on the HydroEdge attribute LengthKm.
g. Attribute: FlowDir. This field indicates flow direction of each river segment
h. Attribute: Agency_ID. This is a unique digit identification number as it appears in the TCEQ, EPA, IBWC, CILA, CNA, SEMARNAT, etc., databases for every river segment. This ID is usually the same as the HydroCode attribute
i. Attribute: SegmentClass. Classified: River Segments or water bodies that are protected by site-specific criteria as outlined in the TCEQ Surface Water Quality Standards. Unclassified: Smaller water bodies that do not have site-specific water quality standards assigned to them, but instead are protected by general standards that apply to all surface water in the state.
j. Attribute: SegmentType. Freshwater Stream: Inland waters which exhibit no measurable elevation changes due to normal tides. Tidal Stream: Descriptive of coastal waters which are subject to the ebb and flow of tides. For purposes of standards applicability, tidal waters are considered to be saltwater. Classified tidal waters include all bays and estuaries with a segment number that begins with 1323xx for the Texas side, all streams with the word tidal in the segment name, and the Gulf of Mexico. Reservoir: Any natural or artificial holding area used to store, regulate or control water. Estuary: Regions of interaction between rivers and near shore ocean water, where tidal action and river flow create a mixing of fresh and salt water.
k. Attribute: Location. Verbal description indicating where the stream segment or water body begins and ends.
l. Attribute: Basin. This field describes the name of the basin. Rio Grande/Bravo basin is the official name within the WQDM
m. Attribute: Region. This field describes the region where the stream segment is located, according to the TCEQ classification on the Texas side and the CNA classification on the Mexican side
n. Attribute: Impaired_Status. Single-character field indicating whether or not the water body was impaired in the 2000 Surface Water Quality Standards effective on September 1, 2000. GIS Maps are available with results about impairing for 2000, but not for year 2002 in the TCEQ website (http://www.tnrcc.state.tx.us/water/quality/data/wmt/data_by_basin.html). These results will be updated for 2002 in the WQDM.
o. Attribute: AgencImpairCode. A one-digit numeric code from the agency indicating why the water body is listed as impaired. This attribute will be related with the Impaired_Code_Table through the CRWR_ImpairedCode attribute.
p. Attribute: CRWR_ImpairedCode. A small integer related to the impaired code from the agency. There will be established a relationship between this attribute and the Impaired_Code_Table to describe why the river segment or waterbody is considered as impaired.
A relationship will be established between a river segment and its corresponding water quality monitoring station (Identified as a Monitoring Point within the geodatabase). Another relationship will be established between the river segments (HydroEdge) and the HydroJunction feature class. The HydroJunction is a virtual point representing a monitoring point in the geometric network.
2.4.2 Feature Class: Monitoring Point
This feature class shows all surface water quality monitoring being conducted by the TCEQ or under TCEQ contract for Fiscal Year 2005 on the Texas side, and all water surface water quality monitoring identified by the CNA and SEMARNAT on the Mexican side. Other type of water quality points such as treatment plants location, waste water discharges, and hazardous points will be included in this feature class within the WQDM. The water quality stations on the US side of the Rio Grande/Bravo basin was downloaded from the IBWC website (http://www.ibwc.state.gov/CRP/monstats.htm), where user can find the monitoring point locations considered in the IBWC-Clean River Project. To support coordinated monitoring, the TCEQ has developed guidance for site selection and for sampling requirements for routine, special study, and targeted monitoring. In this website http://www.tnrcc.state.tx.us/water/quality/data/wqm/coop_monitoring_2005.html TCEQ provides more documents as support for the statewide coordinated monitoring effort on the Texas State.
The water quality stations on the Mexican side of the Rio Grande/Bravo basin were collected from the technical sub direction CNA, and some points published in the CNA website corresponding to the lower Rio San Juan subbasin. These points on Mexico are contained in the Sistema Nacional de Informacion de Calidad del Agua database (http://www.cna.gob.mx/eCNA/Espaniol/Programas/Subdirecciones/SGTCA/sitiossuiba.pdf ).
a. Attribute: HydroID.
It indicates a unique feature identifier in the Water Quality Data Model assigned at the CRWR. This ID becomes the key to establish many relationships between the monitoring point and some elements included in the WQDM. The HydroID for this element would be assigned as described below:
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The first digit indicates the country where the element is located. It was defined the number 1 for the segments located on the US side, and 2 for the segments located on the Mexican side. The next two digits indicate the hydrological sub regions, 9 on the American side and seven on the Mexican side. The next two digits indicate the feature class within the geodatabase; number 01 was assigned to MonitoringPoint feature class that contains the control points in the basin. The last five digits include the number of the element.
2.4.3 Feature Class: Waterbody
This feature class includes the water bodies, impaired or not, located on the Rio Grande/Bravo basin on both sides of the basin. Waterbodies are all the significant ponds, lakes, and bays in the water system. The American waterbodies are gathered from the USGS, EPA, and TCEQ, while the CNA and SEMARNAT provide the waterbodies information on the Mexican side.
2.4.4 Feature Class: Watershed
This feature class includes information related to the drainage areas contributing flow from the land surface to the water system. The watershed information on the Mexican side is collected from the CNA and SEMARNAT, while this is being collected from EPA and TCEQ on the American side. The EPA manages water pollution using Total Maximum Daily Loads (TMDL) defined on watersheds draining to selected river segments or waterbodies, a different watershed layout than that used by the National Weather Service on the US. The WQDM is designed to allow any set of watersheds to be relationally connected to the hydro network, using the “area flows to a point on a line” concept to establish relationships between watersheds and HydroJunctions at their outlet location.
2.4.5 Feature Class: HydroJunction
This feature class includes a set of junctions located at the end of the river segments and at other strategic locations on the flow network. Usually the Monitoring Points, which preserve their original position, are represented by the HydroJunction on the flow network. HydroEdges and HydroJunctions are topologically connected in an ArcGIS geometric network, called the HydroNetwork and included as the backbone of the WQDM. Since HydroJuctions area topologically linked to the river segments (HydroEdges) in the geometric network, the combination of this network and the other relationships means that the classes in the WQDM framework are connected into an integrated data structure.
2.4.6 Time Series table
The inclusion time series data in the WQDM is not only to create a complete water quality data model for using the GIS environment, but also to build a relational database that would be accessible to many water quality models that operate separately of the GIS. The temporal information is captured and stored in a variety formats by each entity, so it is fundamental to have a standard design to manage large historical data sets. The original ArcHydro time series framework for the surface water is being modified to have a large container in GIS that allows storing many variables related to the water quality data that include millions of records. Under this concept, user may acquire, store, or deliver an entire water quality data set, including time series data files from water quality stations, as well as the geographic element associated to it.
2.4.7 TSGroup table
This table describes the entity that manages and publishes some information. In this table users can identify from where the information comes, using a unique identifier for each agency. A relationship is established between the temporal information in the time series table and the Monitoring Point feature class using the FeatureID as the key.
2.4.8 TSType table
The TSType table contains an index of the types of time series data stored in the time series table. A relationship is established between the TSType table and the Time Series table using the TSTypeID as the key.
2.4.9 Impaired Code Table
This table is associated with the HydroEdge and WaterBody feature classes within the WQDM to indicate which river segments are impaired. The impaired code table contains fields to describe which pollutants are responsible for the failure of river segments to meet water quality standards.
2.4.10 Agency responsible table
This table describes which entity is in charge of the water quality stations. A relationship is established between the Agency responsible table and the Monitoring Point feature class using the AgenResp_Code attribute as the key.
2.5 Topology and relationships among the feature classes
A geometric network called HydroNetwork is created to establish the topology among the elements within the WQDM. This HydroNetwork becomes the backbone of the WQDM structure, created from the river segments (HydroEdges) and the water quality monitoring stations (HydroJunctions). The topological connection of its HydroEdges and HydroJunctions in the WQDM enables tracing of water movement upstream and downstream through streams and waterbodies. Relationships built from the HydroJunctions connect drainage areas, waterbodies and any point features such as water quality stations or wastewater treatment plants to the HydroNetwork. Each relationship has a multiplicity, and all the relationships implemented are one-to-many. One-to-many multiplicity means that one HydroJunction may be associated with one or more features in the related class. For example, two HydroEdges (river segments) may drain into a single HydroJunction on a river network
2.6 Data processing
2.6.1 Creating HydroEdges
The original river segments (including the waterbodies) on the US side were extracted from TIGER/Line 92 data to create the initial Designated Stream Segments layer. Where that layer was lacking, missing streams and new reservoirs were table-digitized from TxDOT "half-scale" county map sheets. The Mexican side of the Amistad and Falcon reservoirs and the outlying boundaries of the border lakes were "heads-up" digitized from a digital map created in the early 1980s by the Texas Water Commission (from 1:250,000 AMS map sheets). The hydrography described as HydroEdges in the Rio Grande/Bravo basin geodatabase for the water quantity is being used to define these river segments within the WQDM (figure 1). Fragmented segments were merged in ArcInfo so that each displayed segment was represented by only one record in the table.
Figure 1 Flowline resolution in the Rio Grande/Bravo basin
2.6.2 Creating Monitoring Points
Water quality stations, wastewater treatment plants, and other important control points are being included into the WQDB as a feature class called Monitoring Points. The water quality stations on the US side of the Rio Grande/Bravo basin was downloaded from the IBWC website (http://www.ibwc.state.gov/CRP/monstats.htm), where users can find the monitoring point locations considered in the IBWC-Clean River Project. To support coordinated monitoring, the TCEQ has developed guidance for site selection and for sampling requirements for routine, special study, and targeted monitoring. In this website http://www.tnrcc.state.tx.us/water/quality/data/wqm/coop_monitoring_2005.html
The water quality stations on the Mexican side of the Rio Grande/Bravo basin were collected from the technical sub direction CNA, and some points published in the CNA website corresponding to the lower Rio San Juan subbasin. These points on Mexico are contained in the Sistema Nacional de Informacion de Calidad del Agua database (http://www.cna.gob.mx/eCNA/Espaniol/Programas/Subdirecciones/SGTCA/sitiossuiba.pdf ).
2.6.3 Creating the SnapControlPoint feature class
Because more than two monitoring points could be represented for just one HydroJunction in the geometric network, it is necessary to have one more feature class called SnapControlPoint. The SnapControlPoint is a point feature class that represents all monitoring points with all the features snapped to the right location on the network. The HydroCode is the unique identifier to establish the relationship between the SnapControlPoint and the Monitoring Point feature class. The main purpose of this feature class is to exchange information about water quality parameters between the HydroJunctions participating in the geometric network and the monitoring points, which maintain their original position.
2.6.4 Creating HydroJunctions
Since more than one monitoring point can exist at the same location, it is fundamental to have one point on the geometric network representing all of them. These points participating directly in the network are known as HydroJunctions in the ArcHydro jargon. The HydroID is the key to establish the relationship between the HydroJunctions and the monitoring points. This unique value will be assigned to the JunctionID value of the all monitoring points that are representing, so two or more monitoring points could have the same JunctionID.
2.6.5 Creating a geometric network
A geometric network is crated using the SnapControlPoint and HydroEdge feature classes. All points in the SnapControlPoint feature class are snapped 500 m to the HydroEdge element. In order to avoid dividing the river segments into several parts, this geometric network is built as a complex edge,
Also, the historical information related to the monitoring points is included in the time series table within the WQDM.
2.6.6 DISCREPANCY OF THE HYDROLOGIC DATA
· There are some discrepancies in the information from the stream network RF1 used by the EPA, and the river network reported by the USGS (figure 2). For example, the Costilla Creek river, which is located between Colorado and New Mexico, and lies in the subregion 1302 according to the NHD classification, is an important tributary to the Rio Grande according to the USGS, but it is flowing to nowhere according to the RF1 system (1:500K).
Figure 2 Comparison between RF1 and NHD river network
· A comparison for the river system is shown in figure 3, considering river versions from RF1, NHD (100K scale), and the drainage line produced from the Digital Elevation Model (30 m grid resolution).
Figure 3 River network comparisons among NHD, RF1, and DEM versions
· There are some inconsistencies in the hydrography of the upper basin. Figure 4 shows the comparison of the river network from RF1 and the NHD, after the last one was edited.
Figure 4 Comparison between the RF1 and fixed NHD stream network
3 Results
3.1 River segments
The hydrography described as HydroEdges in the Rio Grande/Bravo basin geodatabase for the water quantity is being used to define these river segments within the WQDM according to the RF1 network from the EPA. A similar river segments schema is proposed on the Mexican side. Originally this hydrography has a scale of 1: 100,000 on USA, while 1:250,000 on Mexico (figure 5). Fragmented segments were merged in ArcInfo so that each displayed segment was represented by only one record in the table.
Figure 5 River segments in the Rio Grande/Bravo basin
3.2 Monitoring Point
Water quality stations, wastewater treatment plants, and other important control points are being included into the WQDB as a feature class called Monitoring Points.
Figure 6 Water quality control points in the Rio Grande/Bravo basin.
3.3 Digital Orthophoto Quadrangles (DOQ)
An orthoimage is remotely-sensed image data in which displacement of features in the image caused by terrain relief and sensor orientation have been mathematically removed. Orthoimagery combines the image characteristics of a photograph with the geometric qualities of a map. The Landsat Mosaic orthoimagery database contains Landsat Thematic Mapper imagery for the conterminous United States. The more than 700 Landsat scenes have been resampled to a 1-arc-second (approximately 30-meter) sample interval in a geographic coordinate system using the North American Horizontal Datum of 1983. Three bands have been selected from the eight spectral bands available for each frame. These are bands 4 (near-infrared), 3 (red), and 2 (green), typically displayed as red, green, and blue, respectively. The image is a full-resolution (spectral and spatial), 24-bit color-infrared composite that simulates color infrared film as a "false color composite".
Purpose:
These data have been created as a result of the need for having geospatial data immediately available and easily accessible in order to provide geographic reference for Federal, State, and local emergency responders, as well as for homeland security efforts. Orthoimages also serve a variety of purposes, from interim maps to field references for earth science investigations and analysis. The digital orthoimage is useful as a layer of a geographic information system. This data can be used to provide reference information for Web browsers and for map applications at a scale of 1:100,000 or smaller. Larger scale orthoimagery such as digital orthophoto quadrangles will be more accurate, but often at the expense of timely updates.
The digital orthophoto was created for every hydrological subregion of the Rio Grande/Bravo basin, as it is shown in figure 7. This is the first time than an orthoimage is created specifically for the whole basin.
Figure 7 OrthoImage of the Rio Grande/Bravo basin
3.4 Further Tasks
· Finish to collect the water quality time series data related to water quality stations (two weeks)
· Import the water quality historical records into the geodatabase (three weeks)
Carlos Patino
Center for Research in Water Resources
e-mail: Carlos_Patino@mail.utexas.edu
These materials may be used for study, research, and education, but
please credit the authors and the Center for Research in Water Resources, The