Project Summary:
The highly variable monsoon rainfall makes the Santa Catalina Mountains, north of Tucson, AZ, an excellent setting to study travel time distributions and water 'age'. With a peak elevation over 9000 ft (nearly 7000 ft above the surrounding desert), the range wrings out a considerable amount of moisture from moist air masses. As a result, there are a number of perrenial streams that create deep, rocky gorges. Using various chemical and physical measures, we can determine how long it takes for water to move through these canyons.
Spatial variability can be a driving force in the timing and magnitude of hydrological activity from the hillslope to the catchment scale. Few studies have investigated spatial variability in rainfall on a scale smaller than 2-3 kilometers. Knowing spatial variability in rainfall is only part of the rainfall-runoff story. How this spatial variability influences active flow pathways and the overall residence time in the watershed is equally important.
To determine this influence, hydrologists often use isotope values to infer information about how rainfall water transitions into stream water. Characterizing water flow pathways and residence times in these complex catchments is important for improving flash flood warning systems, estimating mountain front recharge, managing forest and wildfires, and understanding ecosystem functions. Knowing how water moves through our system, we can identify the first-order geomorphological and topographical controls. These allows for the knowledge gained about our system to be ported to other regions and similar systems.
The main research hypothesis at this study site is that we can make progress in quantifying catchment-water residence times by focusing on the pedo-geomorphologic controls on characteristic hydrological response(s) of landscapes in different climate settings. The central research question is: Can we relate the stream hydrographs, and their water isotopic composition, to different water pathways in order to unravel the complex hydrological functioning of a catchment? The ultimate objective is to improve our fundamental understanding of hillslope flow processes responsible for transport of water and solutes at the catchment-scale.
Our research methods to study and explain travel time distributions:
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are based on the internal structure of landscapes, as observed,
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take account of climate-driven hydrological processes,
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use simple model structures to avoid the curse of dimensionality,
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use auxiliary information to constrain water flow pathways and reduce the problem of parameter uncertainty, and
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provide measures of hydrological similarity that assists regionalization.
This study investigates the spatial and temporal variability of precipitation in monsoon-driven systems and the influence this variability has on the hydrological response (i.e., timing and amount) of the landscape. In order to capture precipitation variability at the appropriate scale of our system, 40 tipping bucket rain gauges were installed in the area draining through Sabino Canyon Dam located in the Santa Catalina Mountain Range. Of these 40 gauges, 32 were located in the 8 km2 Upper Sabino watershed while the remaining 8 were located throughout the 91 km2 Lower Sabino watershed (see figure). These rain gauges record rainfall depths via data logger at an interval of 1 minute. The two rain gauges located at Mts. Lemmon and Bigelow were equipped to automatically collect rainwater samples.