GIS Analysis of Sediment Transport in Humboldt Inlet, California Joshua L. Caulkins

Importance Engineering 2001 US Spent $867,760 and dredged 268,465 yd 3 Mitigation Options Dredging is not cost effective Rationale

Ultimate Goals Better understanding of complex sediment transport processes within the coastal zoneBetter understanding of complex sediment transport processes within the coastal zone Development of new methods with new technologies allow a focus on field studies over lab studiesDevelopment of new methods with new technologies allow a focus on field studies over lab studies Eventual quantification of sediment transportEventual quantification of sediment transport Rationale

Background Adapted from Johnston, 2001

Background

FLOW Background

Study Site

0.7 km 1.8 km 0.8 m/s 1 m/s Summer Winter Humboldt Inlet Characteristics

Peak Ebb Peak Flood Study Site

Dredging March-May (3/98 – 5/98) Dredging April-May (4/99 – 5/99) Dredging April-May (4/00 – 5/00) Post-Dredge Survey (5/98 – 12/98) Post-Dredge Survey (5/99 – 12/99) Post-Dredge Survey (5/00 – 12/00) then second Condition Survey Pre-Dredge Survey (1/99 – 4/99) Pre-Dredge Survey (1/00 – 4/00) Channel Widening August 1999-March 2000 Data Time Line 7/981/ 984/991/005/008/00 No channel overlap Data is spatially and temporally correlated within the channel. No Channel SurveyNo Post-DredgeNo Channel Survey

Dredging Records for Humboldt Bay (Unable to graph data)

Methodology: 1)Imported point bathymetry data into ArcMap GIS. 2)Created a Triangulated Irregular Network (TIN) from depth values. 3)Produced a value grid from the TIN and clipped the grid to the appropriate study area. 4)Calculated a difference map from the clipped grids of each data set. 5)Calculated a difference volume from the difference map.

Net Sediment Gain of 38,642 m^3 (or 50,542 yd^3)

Net Sediment Loss of 798,997 m^3 (or 1,045,049 yd^3)

Net Sediment Loss of 113,877 m^3 (or 148,945 yd^3)

Limitations of Current Analysis: 1) Lack of spatially and temporally correlated data limits depth of study. 2) The small study area does not allow for correction of material removed via dredging. 3) High shoaling areas are known but “reactionary logistics” still dominate maintenance of inlet.

Conclusions & Implications of Current Analysis: 1)Methodology is sound (Ham, Maguire) and cost effective. 2)Quantification ability at this scale is still in the early stages. More exploration into SHOALS or LIDAR data (remote sensing) would enable a more comprehensive analysis.