The website utilizes hydrology data from the United States Geologic Survey and Mexico’s National Institute of Statistics and Geography to provide continuous coverage for the study area.
Sources:
Many features of the website utilize the Hydrologic Unit Code (HUC) System (Watershed Boundary Dataset, WBD) developed by the United States Geological Survey (USGS) with some minor variations explained below. We also display the USGS National Hydrography Dataset (NHD), which depicts lentic and lotic waters of the state. To learn about these datasets visit the USGS website here.
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. 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.
Edits to United States HUC and Mexican subcuenca systems:
- 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) seemed of little use within our comparatively small region. 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 is also our 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. Thus the Rio Grande is uniquely treated and we clipped those US HUCs 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 areas on the borders of some Mexican subcuencas that we determined were errors and removed them.
- Lastly we changed the names of Mexican subcuencas by removing the "R" prefix they all had in common and replacing it with "MEX".