CE 394K GIS in Water Resources
Fall 2002

Development of a GIS Coverage of Impaired
Surface Water Segments in Texas

by

Samantha Hon

Introduction

Purpose

Methodology

Results

Conclusion

Future Work

References

Acknowledgements

 

 

Introduction

    The Clean Water Act of 1972 was amended in 1987 to include storm water discharges. Under this act, states were required to assess the condition of surface waters within their jurisdiction to determine whether they are “fishable and swimmable”. When the water quality of a particular water body is not sufficient to support these beneficial uses, the water body is considered to be impaired and is required to be reported to the Environmental Protection Agency (EPA) as part of Section 303(d) of the Clean Water Act. The document that contains the list of impaired water bodies in the state is referred to as the Section 303(d) list. A portion of the Section 303(d) list is shown in Figure 1. 

    This list gives the exact location of the impaired water body, which area is impaired, what parameter or constituent it is impaired by and also a category and rank. The definition of the categories and ranks are as follows:

Category 5a - a TMDL is underway, scheduled, or will be scheduled
Category 5b - A review of the water quality standards for this water body will be conducted before a TMDL is scheduled
Category 5c - Additional data and information will be collected before a TMDL is scheduled

Rank H - Urgency to initiate TMDL is high
Rank M - Urgency to initiate TMDL is medium
Rank L - Urgency to initiate TMDL is low
Rank S - Standards will be reviewed before a TMDL is scheduled
Rank D - Additional data will be collected before a TMDL is scheduled

    EPA requires that a total maximum daily load (TMDL) be developed for each of the listed water bodies for the constituents that are contributing to the impairment. After a TMDL is developed, dischargers may be required to implement Best Management Practices (BMPs) to reduce their contribution of the pollutant. The Texas Department of Transportation (TxDOT) could be a potential discharger of pollutants resulting from storm water runoff from roads and highways.

Figure 1:A Portion of the Section 303(d) List

Purpose

    The purpose of this term project is to develop a GIS coverage of the impaired segments to aid TxDOT in the determination of where future facilities can contribute runoff to the impaired segments. The most updated list of impaired surface water segments in Texas will be obtained from the Texas Commission on Environmental Quality (TCEQ), formerly known as the Texas Natural Resource Conservation Committee (TNRCC) and imported into a GIS map in a coordinate system that is compatible with that currently employed by TxDOT. The location of all state highways and roads, as well as the boundaries of the TxDOT districts will be overlain on the map of surface waters that are subjected to the TMDL process.

Methodology

    To develop the GIS coverage of the impaired streams, the 303(d) list table obtained from the TCEQ website was first entered into a Microsoft Excel file and then converted to .dbf file that is compatible with ArcGIS. Figure 2 shows a section of the 303(d) list that was developed. From the 2002 Draft 303(d) list, there are 299 impaired water bodies in the state of Texas. The table was set up in a way that if a water body is impaired by a particular contaminant, a "1" is entered under the contaminant column. This is to enable us to query in ArcGIS after we link this table to the basemap.

Figure 2: Section of the 303(d) List in Excel Format

    A coverage of the Hydrologic Unit Codes (HUCs) in Texas was also obtained. This is shown in Figure 3. This coverage was then overlaid with coverages of the streams, lakes, and roads in Texas. The coverage of streams and lakes were obtained from the Texas Water Development Board (TWDB) website. These coverages were then put in a projection that is compatible with what TxDOT uses in creating their maps. This is called the Shackelford Projection and is shown in Table 1 below. However, upon further inspection, it was found that the coverage of streams and lakes from the TWDB website only consisted of the major water bodies in Texas and therefore did not contain some of the streams that were listed on the Section 303(d) list. The coverage that includes the HUCs and the major streams and lakes are shown in Figures 3 and 4.

Table 1: Properties of the Shackelford Projection

Figure 3: Subwatersheds (HUCs) in Texas

Figure 4: Coverage of the Major Streams in Texas

Figure 5: Coverage of the Major Lakes and Estuaries in Texas

    To solve the problem of not having the complete list of streams shown on the coverage obtained from TWDB, I turned to the EPA reach files which has a more complete coverage of the streams in Texas. Although Texas streams are mostly contained in Region 12, there are also some streams on the 303(d) list that are in Region 11 and 13. Therefore, the EPA reach files for Region 11, 12, and 13 were obtained. Figure 6 shows what the streams looks like when overlaid onto the Texas basemap. To make things a little easier, the streams were merged into one layer and then clipped to show only the streams in Texas. This is shown in Figure 7.

Figure 6: Region 11, 12, and 13 Streams Overlaid onto the Texas Basemap

Figure 7: The Merged Streams and Clipped Texas Streams

    However, despite all these efforts, another problem was encountered. The attribute table for the streams in the EPA reach files did not have a common field with the 303(d) .dbf table to allow me to link these together. The 303(d) list that was taken from the TCEQ website contained only a Segment ID (a HUC code and the watershed name also had to be found for each of the segments and entered into the table manually) while the EPA reach files uses a different kind of ID to identify the different streams. At first, it was thought that a Segment ID field could be manually entered into the EPA reach file attribute table for the clipped Texas streams but there were too many records (streams) to go through (about 5000) and this was therefore not very feasible for the scope and timeframe of this project. Also, it was found out later that the EPA reach files also did not contain some of the smaller unclassified streams that are on the 303(d) list. Therefore, the EPA reach files were discarded and another more complete coverage was needed.

    The National Hydrography Dataset (NHD) that was downloaded from the U.S. Geological Survey (USGS) website has a very complete coverage of the streams in Texas. This can be seen in the figures below. Figure 8 shows the basemap of Texas with the HUCs coverage, main Texas streams coverage, and the NHD coverage for Region 12 included while Figure 9 shows a zoomed in look at the difference between the NHD and the main Texas streams coverage. Region 12 was used because it encompassed most of Texas. Another reason why I only worked with Region 12 is because an integrated form of the NHD is now available for this region only. This means that instead of downloading separate files for different subwatersheds from the USGS website, all the subwatersheds can be obtained as one file. This made the data much easier to work with.

Figure 8: Texas Basemap with NHD Region 12 coverage Overlaid

Figure 9: Difference between Main Texas Streams coverage and the NHD Coverage

    The attribute table for the NHD coverage also did not contain a common link to enable the 303(d) list table to be linked to it. Therefore, the only way to solve this problem was to manually locate where the missing streams are on the NHD coverage and extract them out as a layer to be merged with the Texas main streams layer. Figure 10 below illustrates how this was accomplished. The bright blue colored segments make up the Angelina River in the Sam Rayburn Reservoir which is one of the impaired segments listed on the 303(d) list but is not included in the main Texas streams coverage. These segments were selected and exported as a separate layer. This layer is then merged with the main Texas streams layer to produce a layer that contained both main streams and smaller unclassified segments.

Figure 10: Illustration of how Streams from the NHD coverage are Selected

    Next, a coverage of Texas roads and highways was overlaid onto the basemap with the coverage of water bodies. When a query is done on what water body is impaired by what type of contaminant, we can examine what roads are close to the impaired water body. This enables TxDOT to pay closer attention to the runoff from those streets or highways that are within the proximity of the impaired water body. This will not give an accurate assessment on which road or highway are potential contributors to the impairment of a water body that is close by. To do that, the drainage area for the impaired water body needs to be delineated and roads and highways that fall within that delineated drainage area can be said to be contributing to its impairment. This could possibly be included as future work for this project.

Results

    Since so many problems and obstacles were encountered during the course of this term project, there was not enough time to complete the final part of the term project, which was to locate the missing streams on the NHD coverage and merge these streams with the Texas main streams coverage. However, an illustration on how this coverage will be used to query which water bodies are impaired by what kind of contaminant is shown in Figure 11 below. The bright blue lines show the streams that were selected based on a query on pathogens. This means that the water bodies highlighted are the ones that are impaired by pathogens. Figure 12 illustrates the same idea but with lakes and estuaries instead of streams.

Figure 11: Selected Streams based on Query on Pathogens

Figure 12: Selected Lakes and Estuaries based on Query on Pathogens

    Next, we look at what roads and highways are located within close proximity of the impaired water body. This is shown in Figure 13. It can be seen that Gilleland Creek, which is impaired by pathogens, has a few roads or highways that are in close proximity to it or crosses it. These roads and highways are shown below and are FM 685, FM 1825, US 290, FM 973, FM1325 and IH 35.

Figure 13: Coverage showing an Impaired Stream and the Related Roads and Highways

Conclusions

1. ArcGIS is a useful program that can be used to map out impaired streams in Texas.

2. By using the query tool in ArcGIS, we can pinpoint which streams are impaired by a chosen contaminant.

3. This map also enables us to locate roads and highways that are located close to the impaired water body and thus more attention can be paid to those roads and highways to see if they actually do contribute to the impairment.

Future Work

1. Complete the task of locating missing streams from the main Texas streams coverage in the NHD coverage and merge these layers together.

2. Perform a watershed delineation to locate the drainage areas for each impaired streams to give a more accurate account of which roads and highways contribute to the impairment.

3. Perform linear referencing and dynamic segmentation on the streams.

References

Texas Commission on Environmental Quality, "Draft 2002 Texas 303(d) List", October 1, 2002

Texas Water Quality Development Board website, http://www.twdb.state.tx.us

U.S. Geological Survey website, http://www.usgs.gov

Special Thanks....

Dr. David Maidment, Professor at the University of Texas at Austin

Dr. Michael Barrett, Research Scientist, Center for Research in Water Resources, the University of Texas at Austin

Oscar Robayo, graduate student, University of Texas at Austin