Paper No. JAWRA-11-0034-P of the Journal of the American Water Resources Association (JAWRA). Discussions are open until six months from print publication.
Spatial Variability of Pool-Tail Fines in Mountain Gravel-Bed Stream Affects Grid-Count Results1
Version of Record online: 2 FEB 2012
© 2012 American Water Resources Association
JAWRA Journal of the American Water Resources Association
Volume 48, Issue 3, pages 530–545, June 2012
How to Cite
Bunte, K., Potyondy, J. P., Swingle, K. W. and Abt, S. R. (2012), Spatial Variability of Pool-Tail Fines in Mountain Gravel-Bed Stream Affects Grid-Count Results. JAWRA Journal of the American Water Resources Association, 48: 530–545. doi: 10.1111/j.1752-1688.2011.00629.x
- Issue online: 1 JUN 2012
- Version of Record online: 2 FEB 2012
- Received March 16, 2011; accepted November 23, 2011.
- streambed sediment;
- surface fines;
- bedmaterial sampling;
- fluvial processes;
- channel morphology;
- environmental sampling;
- watershed management
Bunte, Kristin, John P. Potyondy, Kurt W. Swingle, and Steven R. Abt, 2012. Spatial Variability of Pool-Tail Fines in Mountain Gravel-Bed Stream Affects Grid-Count Results. Journal of the American Water Resources Association (JAWRA) 48(3): 530-545. DOI: 10.1111/j.1752-1688.2011.00629.x
Abstract: Fine sediment (<2 and <6 mm) particles underlying a 49-intersection grid placed on a streambed at 25, 50, and 75% of the wetted pool-tail width are commonly counted to assess the status and trend of aquatic ecosystems or to monitor changes in the supply of fines in mountain gravel-bed streams. However, results vary even when crews perform nearly identical procedures. This study hypothesized that spatial variability of pool-tail fines affects grid-count results and that a sampling scheme can be optimized for precision and accuracy. Grid counts taken at seven evenly spaced locations across the wetted width of 10 pool tails in a pool-riffle study stream indicated a bankward fining trend with secondary peaks of fines within the stream center. Sampling locations close to the waterlines harbored more than twice as many fines as central locations. Most of the five grid-count schemes derived from the seven sampled locations produced significantly different results. Compared with sampling at all seven locations, schemes that focus near waterlines overpredicted fines, while those that focus on the center underpredicted them. Variability of fines among pool tails was the highest within a broad band along the waterlines; hence, focusing sampling there yielded the most variable results. The scheme sampling at 25, 50, and 75% of the wetted width had the lowest precision and moderate accuracy. Accuracy and precision of grid-count results can be greatly improved by sampling at seven even-spaced locations across the pool tail.