Modeling Oahu’s Watersheds

A comparison of methodologies to determine the best model for monitoring and management purposes.

Amelia Lynch

Background

Why Are Watersheds Important?

    Watersheds are often used:
  1. for management and planning of natural resources
  2. hydrologic modeling
  • Watershed monitoring programs provides information on the conditions of a particular habitat
  • Accurate boundaries are essential to monitor and manage these areas

Hawaii’s Watersheds

Island relies heavily on near by watersheds

With tourism and the population of Oahu growing each year, there needs to be increased protection of natural ecosystems on the island

Hawaii’s watersheds are usually small, with steep elevation, and small drainage basins

Watershed Delineation

A watershed analysis can be influenced by the DEM resolution

A higher-resolution DEM can better define the topographic features and produce a more detailed stream network

Objectives

  1. compare the effectiveness of creating watersheds using different raster data
  1. explain which type of raster data:
  • is most accurate
  • should be used when looking to create management and monitoring strategies

Data Sources

  1. Dr. Maria Estevanez
  2. State of Hawaii Office of Planning
  3. University of Washington

Methods

Using DEM Data

created watershed delineation from DEM data

Using Elevation Points

Displayed the Elevation Points on the Map

Preformed multiple Kriging models on the elevation points

  1. Ordinary
  2. Empirical Bayesian Kriging (EBK)
  3. EBK Regression

Chose best model based on:

  • Root- Mean-Square
  • Average Standard Error
  • Root Mean-Square Standardized

Creating a Second Watershed

Created a watershed using the best Kriging interpolated surface

Comparing Watersheds

Created side-by-side comparison of the two watershed models created from differing elevation raster sources, the DEM and best Kriging model

Results

01 / 06

Elevation Point Data Distribution

right skewed data (not normally distributed)

Square Root Transformation

Cross Validation Ordinary Kriging Summary Report

Cross Validation EBK Summary Report

QQ Normal Plot for EBK Model

Cross Validation EBK Regression Summary Report

Comparison of Kriging Interpolated Elevation Surfaces of Oahu, Hawaii

This map compares the interpolated prediction surfaces of the elevation data from each of the Kriging models used

A Side-by-Side Comparison of Oahu's Stream Network and Watersheds

This map shows the compared watersheds created from the different elevation rasters (DEM and EBK)

Discussion

  • DEMs are more useful for estimating watershed delineations.
  • They provide more elevation points over a larger coverage with much greater accuracy
  • Any organizations that do not use DEMs for their watershed delineations should consider revising
  • Many Elevation Rasters I found did not have full coverage of the island
  • DEMs more accessible to the public will prevent the use of less accurate data
  • Watersheds will be accurately depicted and used for management and monitoring

Data Citations

University of Wahington GIS Data. (2020). The 153 USGS DEM [Data file].Retrieved from  http://rocky.ess.washington.edu/data/raster/tenmeter/hawaii/index.html 

State of Hawaii Office of Planning. (2019). Hawaii Statewide GIS Data [Data file]. Retrieved from http://planning.hawaii.gov/gis/download-gis-data/

Literature Cited

 Bassiouni M. & Oki D.S. (2013) Trends and shifts in streamflow in Hawai‘i, 1913–2008 Hydrol. Processess, 27, 1484-1500.

Hawaii State Department of Business, Economic Development and Tourism (DBEDT), Tourism Research Branch. State of Hawaii Data Book; A Statistical Abstract. (August 2019). Hawaii Tourism Authority, Tourism Research and Records. Honolulu, HI: Research and Economic Analysis Division. Statistics and Data Support Branch.

Kaiser, B.A. (2014) Watershed Conservation in the Long Run. Ecosystems 17, 698–719.

United States, Department of Commerce, Hawaii Office of Planning & Coastal Zone Management Program. Hawaii Watershed Guidance, 2010.

Olkeba T.L., El-Kadi A. I., Kariem H.D., Ghazal A. (2016) Assessment of climate change impacts on water balance components of Heeia Watershed in Hawaii J. Hydrol. Region. Study, 8, 182-197.

Pesce M., Critto A., Torresan S., Giubilato E., Santini M., Zirino A., Ouyang W., Marcomini A. (2018) Modelling climate change impacts on nutrients and primary production in coastal waters. Sci.Total Environ, 628, 919-937.

Richmond R.H., Rongo T., Golbuu Y., et al. (2007). Watersheds and coral reefs: conservation science, policy and implementation. BioScience, 57, 598– 607.

Pulwarty R.S., Nurse L.A., Trotz U.O. (2010) Caribbean islands in a changing climate. Environ: Sci. Policy Sustain, 52, 16-27.