Assessing Deposit Build-up in Corte Madera Flood Control Channel

Science Center Objects

The Corte Madera Flood Control Channel was designed to prevent waters from overflowing Corte Madera Creek in a highly populated area of Marin County. Since the channel was last dredged in 1990 approximately 5,400 cubic feet of sediment has accumulated. The accumulation of sediment is of concern because the sediment may reduce the effectiveness of the channel, posing a flooding threat to neighboring communities.

areal view of corte madera creek

Areal view of corte madera creek

Objective

In order to determine how often dredging operations should take place, research will be conducted on how, and at what rate, channel fill is deposited.

Science Plan

Sediment core samples will be collected along the channel. Data from stratigraphic analysis of the samples will be used to determine if sediment has accumulated gradually or is replaced each wet season. Samples will also be collected downstream and upstream of the channel for comparison. Models will be created to illustrate the accumulation of the two sediment types (episodic vs. gradual). Storm or wet season sediment consists of stacked, graded deposits that abruptly end at the estuary. Gradually accumulated (episodic) deposits consist of normally graded deposits mixed with bottom mud at the end of the estuary.

In addition, geochemical analysis may be conducted to determine to what degree sediment accumulates or is flushed on a seasonal basis. This will be accomplished by measuring two naturally occurring radionuclides in the channel sediment (Berylium-7 and Thorium-234). These become bound to sediment and can be used to determine accumulation in the channel over a set period. (Berryliu-7 is present for a 6 month period and Thorium-234 is only present for 4 months.)