Wohl, Ellen 1
1 Colorado State University
Channel-spanning logjams occur on rivers throughout Rocky Mountain National Park. Each jam creates a backwater area in which finer sediment and organic matter are deposited. Jams thus slow the downstream movement of water, sediment, and nutrients. The backwater at a jam provides insect and fish habitat, so the logjams increase habitat abundance and diversity within streams. By creating obstructions to flow, logjams also enhance overbank flows that spread across the floodplain, depositing fine sediment and organic matter, eroding secondary channels, and creating further aquatic and riparian habitat. Finally, jams enhance exchanges of water between the stream and the subsurface, which mediates fluctuations in water temperature, provides subsurface habitat for aquatic invertebrates, and makes nutrients such as nitrogen available to stream organisms. Understanding the spatial distribution and persistence of logjams is thus important for managing river corridors in the park.
In 2008, I tagged all of the logs in each of 5 large jams with the intent of returning each year to measure exchanges of wood (loss of existing pieces, addition of new pieces). However, 3 of the jams completely disappeared within the next 2 years. In 2010, I began an annual survey of all the channel-spanning logjams on the main rivers in Wild Basin (North St. Vrain, Hunters, Cony, and Ouzel Creeks). In 2012 I added the portion of Glacier Creek between Black and Mills Lakes. Results thus far indicate that the combined effects of fluctuations through time and space in forest mortality (blowdowns, wildfires) and in peak flows (snowmelt and rainfall floods) create substantial variations in the number and size of logjams on rivers within the national park.
Wohl, E. and Beckman, N., 2014, Controls on the longitudinal distribution of channel-spanning logjams in the Colorado Front Range, USA: River Research and Applications, v. 30, p. 112-131.
Wohl, E. and Beckman, N.D., 2014, Leaky rivers: Implications of the loss of longitudinal fluvial disconnectivity in headwater streams: Geomorphology, v. 205, p. 27-35.