Runoff Data

Stream runoff is generally approximated with the use of pressure transducers, similar to the groundwater measurements we use Mini-trolls manufactured by In-Situ. The location of stream gages are shown as S1-S4 on the Gamboa Site Map. There are several methods available to convert depth of water to a volumetric flow rate. The preferred methods are to develop site-specific rating curves or control structures. However due to the time constraints of each of these we subjectively decided to build a weir at S1. The remainder of gages were placed in stream sections where we could take advantage of natural controls in the river. Combined with cross-sectional surveys and hydraulic modeling an acceptable flow estimate can be obtained. We have not yet converted the depth of water measured at each site to volumetric flowrates, however the heights alone still show the relative reponse of each site. The site 'S3' is a large rill in an area that has evidence of frequent overland flow and can be more accurately described as an overland flow detector. 'S4' drains a different part of the hillslope than where most of our instrumentation is located, but provides an excellent gaging station. Detailed cross sectional measurements with a total station were taken at this location to develop a HEC-RAS hydraulic model.

Fig 1 Sharp crested weir flowing during a runoff producing event at site S1, this stream is ephemeral during the wet season at this location but flows continuously further downstream at site S2.