Applicability of the HSPF Model for two Contasting Hawaii Watersheds
Project Objectives
The main objective of this research is to test
applicability of the HSPF model for Hawaii
watersheds. Hypotheses to be tested are (1) HSPF is applicable to Hawaiian
watersheds for predicting annual and monthly streamflow and sediment; and (2)
the precision associated with simulating daily streamflow and sediment is questionable.
The model will be tested on two contrasting watersheds. The specific objectives include:
· Calibrate and validate the model using different
datasets
· Conduct a sensitivity analysis
· Compare and analyze model results
· Evaluate applicability of underlying equations
and assumptions of the model
· Identify strengths and limitation of the model
The results of this study will
identify both the advantages and the deficiencies of applying HSPF and
contribute to a better understanding of sedimentation in Hawaiian watersheds.
The outcome of this study will also assist in assessing problems of Hawaii
watersheds, developing remediation strategies, and progressing the mythologies
and procedures for developing TMDLs and other regulatory concerns for the State
of Hawaii.
Study Sites
Two
watersheds were selected for this research, Kaneohe
on the island of Oahu
and Kawela on the island of Molokai. The two watersheds were selected based on
their contrasting features considered include topology, climate, and land
use.
Kaneohe,
Oahu
The Kaneohe
watershed is located on the windward section of the island
of Oahu, extending from the Koolau
Mountain Range to the Pacific Ocean. It is approximately 14.7 km2. The
watershed population was greater than 15,000 people in the Census 2000. The upper portion of the watershed consists
of various land uses including the Pali Golf Course, Koolau Golf Course, a
banana plantation, the Hoomaluhia Botanical
Gardens, and part of the Kaneohe Forest Reserve,
including sections of three major highways.
The lower portion of the watershed is primary residential and commercial
urban land use. The Hoomaluhia Reservoir
is located in the central part of the watershed (Burr 2003). Average annual precipitation varies from 1000
millimeter to 2000 millimeters (Hawaii Institute of Marine Biology 2007).
Kawela, Molokai
The Kawela watershed is located on the
southeast potion of the island of Molokai, extending from the East Molokai Mountains to the Pacific Ocean. It
is approximately 13.81 km2.
The watershed population was reported as 249 people in the Census 2000 (Hawaii
Institute of Marine Biology 2007). The land use is Evergreen Forest land in the upper and lower portions of the
watershed. The center portion of the
watershed is rangeland. Approximately
90% of the watershed was formerly owned by Molokai Ranch (USEPA 2004). The two of the adjacent watersheds, Kamalo
and Kamakou, are part of the East Molokai Watershed Partnership Conservation
Project Sites (Nature Conservancy of Hawaii
2003). Kawela watershed is part of the Hawaii’s
Local Action Strategy to Address Land-Based Pollution Threats to Coral Reefs program conducted by the EPA and
several other State and Federal agencies.
This project examines ways of
reducing land based pollution from coastal watersheds in an effort to decrease
the degradation of coral reef systems.
Many fencing projects have been conducted in Kawela watershed to protect
the area from feral undulates. In
addition, invasive weed control projects have been implemented. Average annual precipitation varies
from 400 millimeter to 3000 millimeters (Hawaii Institute of Marine Biology
2007).
Watershed
Comparison
These two watersheds have very different
climate, topology, and land use. Kawela
has a greater spatial distribution of rainfall over the entire watershed, where
as Kaneohe has greater rainfall even in low-lying
areas. Kawela’s landscape consists of deep valleys which were formed by
perennial streams. For Kaneohe, the watershed boundary is composed
of extremely steep cliff, with more moderate slopes throughout the rest of the
watershed. The most significant contrast
is the land use. Kawela consists
primarily of forest and rangeland, where as Kaneohe has a mix of many land uses, yet
contains a significant portion of urban areas.