The Sedimentation of Morro Bay San Luis Obispo County, California

The Sedimentation of Morro Bay San Luis Obispo County, CaliforniaEric MohlerGIS 582Spring 2012

IntroductionMorro Bay is a natural embayment located in San Luis Obispo County, California. A natural sandspit protects the harbor and estuary from the incoming Pacific Ocean.

City of Morro Baycoordinates (lat, long):352245N1205112W

WatershedThe bays main contributories are the Chorro and Los Osos Creekwatersheds.

Both drain intoMorro Bays saltmarsh and estuary.

Salt Marsh and EstuaryThe Morro Bay salt marsh and estuary have both been declared ecological reserves due to the abundance of endangered bird and sea life that call them home.

The salt marsh and estuary during low tide as seen from Elfin Forest in Los Osos.A larger and zoomable version of this photo can be found here:http://www4.ncsu.edu/~emohler/Morro-Bay.html

SedimentationIt has all ways been Morro Bays fate to eventually fill in due to sedimentation. However, the sedimentation process has quickened over the recent years.

The areas around the Chorro and Los Osos Creeks have been increasing used for cattle grazing and the cities of Morro Bay and Baywood/Los Osos continue to grow in population. All of it contributing more sediment and pollutants into the watershed.

The Morro Bay National Estuary Program estimates that the estuary could be entirely filled in within the next 300 years due to the increased sediment flow.

Morro RockAdding to the problem is the limited space that allows sediment to drain into the Pacific Ocean.

The most recognizable landmark of the bay, the large volcanic plug known as Morro Rock, was previously unconnected to the mainland. The U.S. Army Corp. of Engineers built an artificial barrier to Morro Rock to help stabilize the waters inside the harbor.

This leaves one small entrance for boats to get in and sediment to get out.

DredgingIn order to keep the bay safe for boat travel and commercial growth, dredging operations must be carried out on the mouth of the bay every year and the inside of the harbor every three to four years.

Dredging is damaging both to the estuary from which the sediment is taken from and the area that the sediment is dropped.

Image from The Tribune at SanLuisObispo.comand their article Major dredging about to begin in Morro Bays harbor channel

Click picture for link.

Project Goal The goal of this project is to find ways of modeling the sedimentation process in Morro Bay and the accompanying watershed.

With a successful model, it may be possible to find ways of slowing the sedimentationprocess and preventsuch a biologically diverse, geographical unique, and commercially successful region from being lost before its time.

DataThe following datasets were used in this project:

A 10m DEM of the Morro Bay Area from the USGS.

A 2003 shapefile the Morro Bay watershed that was made for the Central Coast Wetlands GIS project and distributed by the County of San Luis Obispo GIS department.

The 10m DEM with the raster version of the watershed shapefile.

DataThe following were also used:

A 1m DEM of Morro Bay created by the CA Coastal Conservancy Coastal Lidar Project in 2011.

A 1996, 2001, and 2006 raster of land cover complied by The Coastal Change Analysis Program.

1m DEM from the CA Coastal Conservancy Coastal Lidar Project

MethodTo model the sedimentation process, many variables need to be known. Among them are:

SlopeAspectRainfall amountsSoil type or land cover

Slope and AspectSlope, or the change in the gradient, is needed to determine how quick water flows over the surface.

Aspect, or the direction of the gradient, helps determine which way water flows.

Aspect as derived from the 10m DEM

Land CoverKnowing the land cover and/or soil type of the area is very important for modeling sedimentation.

It helps determine how much rainfall actually turns into runoff and how likely it is to erode and enter the stream as sediment.

This project intends to compare potential sediment runoff using land cover data from 1996, 2001, and 2006.

The Part Where I Admit That Im Nowhere Near DoneUnfortunately, much work still needs to be completed on this project.

I still need to find rainfall data before a simple model can be created.

The final model will be completed for the project paper.