SEDIMENT TREND ANALYSIS IN THE LOWER BUFFALO RIVER AND OUTER HARBOR: EVIDENCE SUPPORTING UPRIVER TRANSPORT OF SEDIMENT BY THE LAKE ERIE SEICHE

The identification of the source(s) of sediment deposited around the mouth of the Buffalo River and Buffalo Outer Harbor (e.g., Lake Erie derived sediment, plumes of sediment-laden river water formed during high flow events, or a combination of sources) and the potential for re-entrainment and transport upriver by lake seiche has been evaluated by conducting a Sediment Trend Analysis (STA). STA is a method whereby patterns of net sediment transport are determined by relative changes in the grain-size distributions of sedimentary deposits. This effort directly builds upon previous investigations of sediment dynamics in the Buffalo River. STA and side-scan sonar results confirmed the presence of a bidirectional flow regime within the Buffalo River. During times of high flow, a river-dominated transport regime exists; times of lower flow can coincide with Lake Erie seiche producing a seiche-driven upriver transport regime capable of carrying sediment ~4.5 km upriver. Four Transport Environments (TE) were identified – TE1: Lake Erie, TE2: Outer Harbor, TE3: Black Rock Canal, and TE4: Buffalo River Entrance. With the exception of the TE4, all transport was determined to be northwards into the Niagara River. TE4 indicated that sediment from outside the river mouth was moving upriver, as well as circulating to join the directions of sediment movement found in the adjoining TEs. The upriver transport regime of TE4 was in excellent agreement with previous STA studies and can be explained by rising Lake Erie seiches able to entrain sediment previously deposited in the Buffalo Harbor. In the Outer Harbor, sedimentation patterns derived from STA also were correlated to digital side-scan sonar records used to evaluate bottom morphology and presence of significant sedimentary features. Management decisions for sediment remediation in the middle and upper portions of the Buffalo River Area of Concern, including evaluation of best alternatives, should take into account the lower portion of the river where the influence of Lake Erie seiches and the sediment movement from near the river mouth upstream is most pronounced.