Lower Rio Grande Valley Groundwater Transport Model Page: PAGE 5
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MONTGOMERY Conceptual Model Report:
Lower Rio Grande Valley
I& ASSOCIATES Groundwater Transport Model
southeast. Digital elevation model (DEM) datasets (1 arc-second resolution, or
30 meters were obtained for the study area from United States Geological
30mees)weeobaie fr h suy arafo ntdSae elgclSurvey
(USGS) National Elevation Datasets. Land surface elevation in the study area is
shown on Figure 2.1.2.
Surface water features in the study area are shown on Figure 2.1.3. The major
river basins in the valley are the Rio Grande Basin and the Nueces-Rio Grande
Basin. The Rio Grande flows along the southern margins of the study area and
' empties into the Gulf of Mexico. The gradient of the river is smaller than the
slope of the upland plain to the north, except near the gulf where the river lowland
and the upland plain merge into the delta of the Rio Grande (Baker and Dale,
I 1964).
The climate in the valley varies from subtropical to semi-arid, as shown on
Figure 2.1.4. Thirty-year averages (1981 through 2010) for precipitation and
temperature were computed using climate data obtained from the PRISM Climate
Group (Daly and others, 2008). The thirty-year average annual temperatures
range slightly over the study area from about 71 degrees in the north to about
75 degrees in the south, as shown on Figure 2.1.5.
The thirty-year average annual precipitation in the valley increases from about
19 inches in the southwest to about 28 inches in the east along the coast as shown
on Figure 2.1.6. Average monthly precipitation for selected rain gage sites cross
the valley is shown on Figure 2.1.7. Rainfall occurs mostly from thunderstorms
in the spring and occasional hurricanes in the late summer and fall. These storms
often generate large amounts of rainfall over short periods of time, which results
in flooding due to the relatively flat terrain of the region (Black & Veatch, 2015).
Total average annual precipitation for the study area for 1980 through 2013 is
shown on Figure 2.1.8.
Information on net lake evaporation was obtained from the TWDB (2016b) for
1-degree quadrangles in the study area. Net lake evaporation across the valley is
shown on Figure 2.1.9. Average annual net lake evaporation ranges from about
60 to 65 inches along the coast to about 61 inches in the upland areas.
2.2 Soils and Vegetation
Hydrologic Soil Groups (NRCS, 2007) were classified from SSURGO soils using
the National Resources Conservation Service (NRCS) Soil Data Viewer. The
NRCS defines Hydrologic Soil Groups as:
PAGE 5
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Montgomery & Associates. Lower Rio Grande Valley Groundwater Transport Model, report, June 30, 2017; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth1114946/m1/21/: accessed July 17, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.