Characteristics of Boulder's creeks

Characteristics of Boulder's creeks
Before white settlement and now

Then

1885 photo of Boulder Creek, showing braided channels, courtesy Denver Public Library Western History Collection, Pooley, P-1734

Water impoundment pattern: Beaver dams were the only impoundments along the creek. Beavers were almost wiped out by the mountain men in Colorado in the 1820s.

Flow pattern: A huge snow-melt peak in the spring would drop rapidly to almost nothing the rest of the year. Occasional rains would bring the creek back up.

Flood pattern: Annual spring floods and infrequent monsoon events scoured channels frequently. Floods carried large amounts of debris which plugged channels and toppled trees.

Channel pattern: Broad shallow channels probably developed on the plains, becoming wider as one went downstream. The creek had multiple braided channels and changed channels from time to time.

Sediment pattern: Spring floods and thunderstorm events carried large amounts of sediment through the creek system (west to east), replenishing nutrients, filling creek channels and then down-cutting new channels in the same or different locations.

Vegetation pattern: It is believed that native willows and a few trees, primarily Plains Cottonwoods, were present in riparian zones on the plains.

Riparian pattern: The riparian zone was confined to the creek and its multiple channels.

Now

2009 photo of Boulder Creek, showing more trees, channel narrowing, introduced plants and encroaching development.

Water impoundment pattern: Multiple upstream and downstream reservoirs (Gross, Barker, Valmont Lakes) catch the spring run-off and store it.


Flow Pattern: A smaller peak in the spring drops more slowly to a higher summer-time irrigation flow. Winter flows are diverted to storage. Minimum flows are maintained on a few streams. Occasional rains still affect creek levels.

Flood pattern: Spring flooding is rare. Infrequent monsoon events are the primary times that channels are scoured, trees are uprooted and debris is swept out of riparian areas.

Channel pattern: A single well-defined channel stays in the same location. The channel generally narrows from vegetation encroachment as one goes downstream, as all types of diversions take more and more water from the creek.

Sediment pattern: Sediment from the mountains is caught behind Gross Reservoir, Barker Dam and Silver Lake Dam. Much of the sediment coming into Boulder Creek is from sanding and salting roads in the winter. Creeks are down-cutting their channels, as less sediment comes into the system.

Vegetation pattern: Large numbers of trees crowd creek channels. Exotic species predominate in many areas. Creeks become more choked with vegetation the further one goes downstream.

Riparian pattern: The riparian zone spreads from the creek out along irrigation ditches and into laterals, irrigated fields, and waste ditches.

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