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Unfortunately, the USGS has not created HUCs throughout the study area, into Mexico. U.S. HUCs cover a small part of Mexico extending from U.S. HUC’s, across the border a short distance into Mexico. This is no surprise since the system was developed for the United States, but in order to expand our study area into Mexico (major addition for Version 3 of the website and database) we had to implement a similar system that could work in concert with the U.S. USGS HUC system. Mexico’s National Institute of Statistics and Geography (INEGI) created a similar, albeit completely independent, system with three levels of nested hydrologic connected areas. We used their lowest ‘subcuenca’ level, which we though sufficiently similar to USGS HUC 8s to provide a complete hydrological watershed boundary dataset for the study area.
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- We utilized most HUC levels, from small HUC 12s to larger HUC 6s as shown in our map tab’s layers. However, lower level (larger shapes), which combine Texas' major river basins, seemed of little use within our comparatively small regionfor users of our data. Instead, we combined HUC 8 and Mexican subcuencas into major river basins that we thought most biologists interested in aquatic ecosystems would find useful. See our Major River Basin layer in the map tab – this layer is also our official study area.
- We decided to edit the shapes of US HUCs along the Rio Grande that overlapped with Mexico in order to maintain functionality of the website. Allowing overlapping hydrology systems, which we initially preferred, proved to be problematic for a number of reasons, so we decided to edit the shapes of U.S. HUCs along the Rio Grande that overlapped with Mexico. Thus the Rio Grande is uniquely treated and we clipped those US HUCs unique because those U.S. HUCs allong the Rio Grande were clipped to meet the Mexican subcuencas, which stop immediately at the Rio Grande. Users should understand that checklists and HUC assignments to occurrences are based on these edited shapes. Furthermore, the Rio Grande, cannot be treated as having hydrologically nested HUCs standard across the US portion of the study area.
- We noticed small Small areas on the borders of some Mexican subcuencas that we were determined were to be errors and were removed them.
- Lastly we changed the The names of Mexican subcuencas were edited by removing the "R" prefix they all had in common and replacing it with "MEX".
How are hydrologies used
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The current version of the website displays the NHD dataset as a layer on the map tab, but the NHD is not utilized in other ways. Mexican subcuencas and the USGS’ WBD HUC system levels 12 through 6 are used throughout the website, together forming a merged continuous hydrology covering the entire FoTX study area that is used for summarizing and displaying data as described below:
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