Title

Stream Characteristics of Arroyo Zarco

Presenter Information

Jared Duffy
Philip Rush
Kenny Terrile

Document Type

Oral Presentation

Location

SURC Ballroom C/D

Start Date

15-5-2014

End Date

15-5-2014

Keywords

Gradient, Debris Flows, Sediment

Abstract

We investigated the influence of external factors on sediment size and stream gradient in an ephemeral stream channel, the Arroyo Zarco at Chamela, Jalisco, Mexico (19˚30′N, 105˚3′W). The external factors that we examined were tributary streams, woody debris, and debris flows. We hypothesized that these factors would cause a reduction in the stream gradient, and an increase in sediment size. We surveyed the longitudinal gradient of a 600-m reach of the Arroyo Zarco, surveyed channel cross-sections at noticeable transitions between sediment sizes, and measured average sediment size at each cross section. We calculated the average surface sediment size at each cross-sectional area using a step-randomization method. To determine change in stream gradient, we measured the change in elevation every 10 meters along the channel using a surveyor’s tape measure and leveling scope. Qualitative observations of sediment size, presence/absence of the listed external factors, and presence of bedrock were noted every 10 meters along the stream channel. The locations of all sites were documented with a Geographic Positional System (GPS) instrument for subsequent mapping of the channel changes. The sediment size was larger downstream of debris flows and tributary streams, as we predicted. In contrast, sediment size was smaller downstream of accumulations of large woody debris. A change in gradient was correlated with tributaries, debris flows, and woody debris, but not all change in gradient was due to these external influences. The results, therefore, partially support our hypothesis.

This presentation received a College of the Sciences Best Poster Presentation Award for 2014.

Poster Number

37

Faculty Mentor(s)

Ely, Lisa; Beck, Daniel

Additional Mentoring Department

Biology

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May 15th, 8:30 AM May 15th, 11:00 AM

Stream Characteristics of Arroyo Zarco

SURC Ballroom C/D

We investigated the influence of external factors on sediment size and stream gradient in an ephemeral stream channel, the Arroyo Zarco at Chamela, Jalisco, Mexico (19˚30′N, 105˚3′W). The external factors that we examined were tributary streams, woody debris, and debris flows. We hypothesized that these factors would cause a reduction in the stream gradient, and an increase in sediment size. We surveyed the longitudinal gradient of a 600-m reach of the Arroyo Zarco, surveyed channel cross-sections at noticeable transitions between sediment sizes, and measured average sediment size at each cross section. We calculated the average surface sediment size at each cross-sectional area using a step-randomization method. To determine change in stream gradient, we measured the change in elevation every 10 meters along the channel using a surveyor’s tape measure and leveling scope. Qualitative observations of sediment size, presence/absence of the listed external factors, and presence of bedrock were noted every 10 meters along the stream channel. The locations of all sites were documented with a Geographic Positional System (GPS) instrument for subsequent mapping of the channel changes. The sediment size was larger downstream of debris flows and tributary streams, as we predicted. In contrast, sediment size was smaller downstream of accumulations of large woody debris. A change in gradient was correlated with tributaries, debris flows, and woody debris, but not all change in gradient was due to these external influences. The results, therefore, partially support our hypothesis.

This presentation received a College of the Sciences Best Poster Presentation Award for 2014.