San Antonio Missions National Historical Park
Hydrogeology
The availability of a constant, reliable water supply has greatly affected human cultural geography. In a semi-arid land like south-central Texas , the spring-fed San Antonio River has been a cultural oasis for centuries. The importance of this water is evident throughout the 331 hectares of San Antonio Missions National Historical Park (SAAN). Indeed, the missions would not have been built if not for the river as missionaries and native peoples (the Coahuiltecans) irrigated their fields via an intricate system of acequias – gravity-driven ditches tapped into the river above a dam.
Today the river, and its supplying aquifer, still plays a vital role in supplying the ever-growing demand of drinking water for the San Antonio area. The San Antonio River 's course is heavily altered through flood control channels as it flows through the center of the city and the park. While the park does not own any portion of the San Antonio River – it does own land down to the high-water mark in some areas – the quality and quantity of water plays not only an important aesthetic interpretative backdrop, but also directly supplies flow to the acequias which are owned and maintained by the park. The park retains water rights to the two remaining mission acequias – the active Acequia de Espada, flowing along the west side of the river, and the currently inactive Acequia de San Juan on the east side. The park plans to soon open flow into the Acequia de San Juan – inactive for over 40 years – upon remediation of a hazardous spill site along its course. The park also manages a short segment of Piedras Creek, from the Acequia de Espada Aqueduct to its confluence with the San Antonio River .
The San Antonio River leaves the greater urban area and becomes a free-flowing, undeveloped stream to the south. Approximately 100 km downstream the river flows along the Ranchero de las Cabras unit – used during mission times to graze livestock. The Ranchero de las Cabras also includes the seasonal Picosa Creek, which joins the San Antonio River in the park.
Sample Site Locations
Piedras Creek (SAAN_PCPC Coordinates (NAD 83) 29 19 56.7, 98 27 40.8 ) Piedras Creek will be monitored as it enters park lands at the crossing of Acequia de Espada Aqueduct. Piedras, also know as Six Mile Creek, drains a highly urbanized watershed west of the river and has displayed elevated nutrients during high flow.
Acequia de Espada (SAAN_AEAE Coordinates (NAD 83) 29 19 43.4, 98 27 42.8) This site is directly superjacent to the Piedras Creek site, and representative of waters of the Acequia de Espada. Note heavy growth of Hydrilla verticillata.
San Antonio River (SARA site 17066 Coordinates (NAD 83) 29 55 48, 98 29 24)This site is not within the park but directly upstream of the Missions Unit and is routinely monitored by the SARA. Note the river flows within a flood-control channel at this site.
San Antonio River (SARA site 12897 Coordinates (NAD 83) 29 19 12, 98 27 0) This site is located immediately downstream of the Missions unit. It is routinely sampled by the SARA. Again, the river flows within a flood control channel through this site.
San Antonio River (SARA site 12883 Coordinates (NAD 83) 29 10 12, 98 12 0) This site is directly upstream of the Ranchero de las Cabras Unit and is routinely sampled by the SARA. Note at this point the river is free-flowing in a natural channel.
Parameters Collected
Field Data
Site ID code
Sample Collection Date
Sample Collection Time
Days since last significant rainfall
Secchi Depth (m)
Specific Conductance (µS)
Dissolved Oxygen (mg/l)
Flow (cfs)
Flow Severity
pH (SU)
Water Temperature (C)
Laboratory Data
Ammonia-N (mg/l)
Chloride (mg/l)
Nitrate/Nitrite – N (mg/l)
Sulfate (mg/l)
Total Phosphorous
Total Kjeldal Nitrogen
Data Folder Tree
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