Channel Morphology Controls on Sediment
Transport in Jordan Creek, Schnecksville, Pennsylvania, U.S.A.
Young, R., Horner, A.,
Dowdy, N., Van Zee, A., Musa, D., Hillegas, L., Burns, S.,
Sherwood, W., Rock, M., and Sewall, J., 2014,
Channel Morphology Controls on Sediment Transport in Jordan Creek,
Schnecksville, Pennsylvania, U.S.A.: Geological Society of America
Northeastern Section - 49th Annual Meeting (Lancaster, PA, March
23–25, 2014) Paper No. 40-3.
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 7-20 cm cobbles
(60-80%) and 0.4-2 cm 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.
Channel Morphology Controls on Sediment
Transport in Jordan Creek, Schnecksville, Pennsylvania, U.S.A.