A psuedo-natural breaching of the Carmel Lagoon*

Spring 2003

(*see notes on Slide 2)

by Paul Huntington

Watershed Institute CSUMB

• This presentation was prepared by Paul Huntington, a student in Doug Smith’s geo-hydro class at CSUMB

• These notes were added by Fred Watson at CSUMB, revised June 2003 after some clarification thanks to Kevan Urquhart at CDFG

• The psuedo-natural breach shown is a post-winter phenomenon that occurs after river inflow subsides to the point that there is insufficient flow to keep the sand bar open; but before inflow ceases altogether. This can lead to a slow rise in the lagoon stage to the point where it spills over the sand bar and breaches, staying open briefly until ocean waves close the sand bar once more

• We use the term ‘psuedo-natural’ because the breach occurred over a sand bar that had already been artificially breached in the same flow season

• Fully natural breaches are rare. Normally, when inflow causes to the lagoon to overfill, local agencies work to catalyze a breach manually (using earth moving equipment) in order to minimize the risk of flooding houses near the lagoon. Further, most (all?) streams on the California Coast with lagoons that breach have some form of water development that has altered the flow regime in some way – with likely downstream effects

•Knick point?

•Change in Base level?

•How would you characterize the flow?

I think we can cross??

Advice: Error on the side of Caution!!

Super Critical Flow

Widening of Channel

http://home.csumb.edu/s/smithdouglas/world/essp%20460/images/antidun.mov

Destabilizing/undercutting banks

Within 20 minutes!!!

Suspended Sediment Load•Is it a hydraulic drop?

• Super Critical Flow?

A Surfers Dream!

…and the Waves Grew…

Channel Widens and Velocity increases

Migrating up river

Looking back toward Lagoon following initial drainage

March 15,2003

4:00pm

March 15, 2003

5:30pm

•Gully Formation

•Incised River Systems

•Base Level Change/Tides and Discharge rate

…and a River runs through it.

by Paul Huntington

Watershed Institute CSUMB