Disturbance Regime in Unglaciated Unconfined Channels

Picture of an unglaciated unconfined reach

(Photo by L. Polvi)

Debris Flows - Unglaciated Unconfined Channels

Unglaciated regions of the Colorado Front Range lie below 2,300 m, which coincides with a hydrograph dominated by rainfall, as compared to snowmelt above 2,300 meters.

Hillslopes are not as steep, but that appears to have less to do with debris-flow initiation in the Front Range than with ravel and overland flow.

Wildfire occurs more frequently in these unglaciated zones and may enhance debris slide initiation.

Debris will not contribute as much sediment to the channel relative to confined sections, but the woody debris and sediment deposited may have a longer retention time.

Floods - Unglaciated Unconfined Channels

(Information compiled by Liz Gilliam)

Unglaciated regions of the Colorado Front Range lie below 2,300 m (7,500 ft), where rainfall-produced floods predominate.

The large discharge per unit drainage area produced by convective storms will inundate floodplains and cause the most enhanced deposition in these wider, low gradient segments.

Roads are generally constructed alongside the channel in these zones and reduce the lateral migration of the channel, increasing flood destruction and potentially increasing debris-flow occurrence.

Greater flood attenuation occurs in these reaches due the broad floodplains, effectively reducing in-channel flows to a pre-flood level.

Beaver may have been more active in the unconfined reaches in the past, influencing hydrologic and flood characteristics.

Picture of unglaciated unconfined reach