21-2 Effects of Stream Discharge Variance, Seasonality, and Trend on Alluvial Sediment Character – A Pilot Study

Session: Functions of River Corridors, Floodplains and Wetlands (Posters)

Presenting Author:

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Abstract:

Alluvial deposits have historically been correlated primarily to stream planform for the purpose of establishing facies models. Recent work, however, has shown that discharge variability in rivers may be a more fundamental control on the resultant facies. Recent work has determined that there is a strong correlation between the coefficient of variance of annual peak discharge (CVQ_p) and alluvial deposit character. However, the question arises as to what other controls on discharge may affect alluvial deposition, accumulation, and preservation. To examine this, we have conducted a pilot study examining several possible factors. In this study we re-examine CVQ_P, and correlate seasonality and potential long-term trends in discharge to the CVQ_P and thereby to the preserved sediments.

We examined hydrographic data at sites along six rivers in the USA where the alluvial stratigraphy is already well-understood at or near the location where discharge data were collected. Annual peak, daily mean, and monthly mean discharge statistics were sourced for each location. All data were collected from the USGS Water Data website. The selected streams represent a range of CVQ_P values determined from previous work; all are located in the center of the United States, from Texas to Montana, all with at least 90 years of hydrographic data.

For each site, the CVQ_P was recalculated, and additional calculations for the per-month and daily mean variances were also performed. Each annual variance matched previous work at the same site; monthly variance increased in each of the six locations, and daily variance was greater than monthly in all cases but one. Seasonality was recorded with both an index calculation as well as observing results from the USGS hyswap python program. The index method only correlated to CVQ_P for the highest and lowest variance stream, while the hyswap data did not show any correlation. In order to determine whether each site experienced a significant trend of change in discharge, both a Mann-Kendall (MK) and Innovative Trend Analysis (ITA) test were run. Only the highest CVQ_P site exhibited a trend per MK testing and was the only site with a decreasing ITA trend. Overall, no investigated variable appears to exhibit a strong correlation to either CVQ_P or sediment character. A more comprehensive study will include more variables and international locations.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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