Paper No. 3
Presentation Time: 8:00 AM-12:00 PM
CHANNEL MORPHOLOGY CONTROLS ON SEDIMENT TRANSPORT IN JORDAN CREEK, SCHNECKSVILLE, PENNSYLVANIA, U.S.A
Variations in fluvial channel morphology, flow characteristics, and sediment transport are linked. To quantify some of these relationships, we measured two transects across Jordan Creek on October 7, 2013. Jordan Creek is a 34-mile-long tributary to the Lehigh River in Lehigh County, PA. In the vicinity of our sampling sites, Jordan Creek has a drainage basin area of 137 km2 and discharge in October 2013 varied from 0.5 – 4.4 m3s-1. Our sampling sites were upstream from the USGS stream gage in Schnecksville, PA. Transect A (40°39’21.5”N, 75°37’47.7”W) was approximately 20 m downstream of Transect B (40°39’21.4”N, 75°37’50.7”W). At both transects, we measured the width and sampled velocity, suspended sediment, and bedload lithology at regular intervals. In the lab, we created profiles of both transects, calculated discharge, and performed loss on ignition to differentiate organic and inorganic suspended load. Transect A was 19 m wide with a maximum depth of 0.44 m and a maximum velocity of 0.9 ms-1. Transect B was 29 m wide with a maximum depth of 0.53 m and a maximum velocity of 0.6 ms-1. Bedload across Transect A varied from a mix of 7-20cm cobbles (60-80%) and 0.4-2cm pebbles (20-40%) to 100% 30-32cm boulders in the thalweg. Bedload across Transect B varied from 100% silt and clay to poorly sorted cobbles (50%) and coarse sand/fine pebbles (50%) in the thalweg. Suspended load across Transect A was highest near the banks with the maximum load (333.33 mg/L) in the thalweg. Suspended load across Transect B was more uniform (~130 – 200 mg/L) across the entire transect. Considering both transects, a 34% reduction in width and a 17% reduction in depth increases flow velocity by 50%. A 50% increase in flow velocity is associated with a transition from poorly sorted sand and small-to-medium pebbles upstream to well sorted large cobbles and small boulders downstream. In addition, the broader transect (B) has a more uniform velocity profile, which is associated with an even distribution of suspended load. These results suggest that persistent differences in channel morphology can result in significant lithological differences in close proximity. In regions like the Appalachians where entrenched drainages are common, this supports the idea that features of the underlying bedrock exert strong control on facies distribution in fluvial systems.