Reconnaissance sediment budget for selected watersheds of West Maui, Hawai‘i

Open-File Report 2015-1190
By: , and 

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Abstract

Episodic runoff brings suspended sediment to the nearshore waters of West Maui, Hawaiʻi. Even small rainfalls create visible plumes over a few hours. We used mapping, field experiments, and analysis of recent (July 19–20, 2014) and historic rainfall to estimate sources of land-based pollution for two watersheds in West Maui: Honolua, and Honokōwai. Former agricultural fields and some unimproved roads are plausible sources for polluted runoff, but have saturated hydraulic conductivities greater than the 10–15 millimeters per hour (mm/hr) rainfalls of July 2014. These fields and roads showed minor evidence for storm runoff, and could not have contributed substantially to July 2014 plume generation. Since 1978, rain at intensities capable of causing runoff from former agricultural fields sustained for 1–2 hours is also rare; such intensities have 2–5 year recurrence rates in the north, and greater than 25 year recurrence rates to the south near Lahaina. Streambanks now eroding into historic terraces of sands, silts, and clays are a more plausible source. Although past large storms contributed to sediment loading, annual plume generation is now caused by smaller rainfalls eroding these near-stream legacy deposits. Treatments of former agricultural fields, roads, and reserve forests are consequently not likely to measurably affect sediment pollution from smaller, more frequent storms. Increased runoff from the development of West Maui has the potential to exacerbate sediment plumes from such storms unless there is an effective strategy to reduce bank erosion. Uncertainties in the extent and erosion rate of historic terraces, however, limit our ability to plan mitigation.

Suggested Citation

Stock, J.D., Falinksi, K.A., Callender, T., 2015, Reconnaissance sediment budget for selected watersheds of West Maui, Hawai‘i: U.S. Geological Survey Open-File Report 2015–1190, 42 p., http://www.dx.doi.org/10.3133/ofr20151190.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Methods
  • Results
  • Discussion
  • Conclusion
  • Acknowledgments
  • References Cited
  • Appendix

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Reconnaissance sediment budget for selected watersheds of West Maui, Hawai‘i
Series title Open-File Report
Series number 2015-1190
DOI 10.3133/ofr20151190
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description v, 42 p.
Country United States
State Hawaii
Other Geospatial West Maui
Online Only (Y/N) Y
Additional Online Files (Y/N) N