Flood Control Debris Basins

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7_BEACON Tech Report (FINAL)

4.1.1

Flood Control Debris Basins

There are currently over 16 flood control debris basins in Santa Barbara County and over 30 in

Ventura County (Ventura County 1999). Figure 4-3 and Figure 4-4 show the locations of the

basins as presented by the Santa Barbara County Flood Control District and the Ventura County

Flood Control District, respectively. As shown in Figure 4-3, the debris basins in Santa Barbara

County are generally located within five to ten miles of the coastline. In Ventura County

(Figure 4-4), the basins are generally located within 10 to 20 miles of the coastline. The

increased distance to the debris basin in Ventura County is caused by the regional geology, where

the mountains and respective watersheds are located further inland.

The debris basins act to trap sediment and debris (Figure 4-5) that may otherwise travel

downstream and cause flood control problems. The flood control districts periodically clean out

the debris basins, with heavy earthmoving equipment. Normally, the material removed from the

basins is used for landfills or sold to contractors. The purpose of this program is to place the

beach-compatible material on one of the six beach fill sites instead of the usual upland disposal

locations. Delivery of debris basin sediment involves removal of incompatible material such as

brush and boulders at the site. Removal of this material may be accomplished through

mechanical sifting and reworking of the sediment using conventional earthmoving equipment

(Chambers 1992) (See Section 4.2.5). The beach compatible material could then be hauled to the

beach via trucks.

As mentioned, debris basin infilling is sporadic and depends on the precipitation that occurs

during any given year. Heavy infilling events tend to occur about every five years (Bailard

1990). However, basin cleanout does occur more frequently.

4.1.2

Rivers, Creeks, Sloughs, and Marshes

Another potential source of sandy material comes from rivers, creeks, sloughs, and marshes. The

Ventura River and the Santa Clara River have historically provided large quantities of sediment

to the littoral cell. However, the sediment supply has slowed since construction of dams

upstream. Portions of the Ventura and Santa Clara Rivers are periodically excavated as flood

control measures. Sediments produced by this excavation could be placed on the beach to help

offset the volume of sediment that is trapped upstream behind dams and other flood control

devices. Due to a limited amount of available information, specific volumes were not estimated

for this type of excavation event. In addition, the Santa Clara River Enhancement and

Management Plan (Ventura County 1999) lists recommendations for each reach of the Santa

Clara River and identifies potential mining areas as shown in Figure 4-6.

The Goleta Slough, which is under the administration of the Santa Barbara County Flood Control

and Water Conservation District and Water Agency (SBCFCD), is a potential source of beach

quality material.

During the severe winter storms of 1995, 400,000 cy of sediment was

deposited in the Slough (200,000 cy on January 10 and 200,000 cy on March 10). However, this

large volume is not always available in the Slough. For instance, the SBCFCD is currently

dredging 25,000 cy from the slough. For general estimating purposes, it is assumed that the

Goleta Slough and its tributaries may yield an estimated volume of between 25,000 to 200,000 cy

of sediment.

4-3

Moffatt & Nichol Engineers