A significant reduction in flood damage and erosion across urban Honolulu can be achieved by protecting native forests and controlling invasive species in the Ala Wai watershed, according to a new study by researchers at the University of Hawaiʻi Economic Research Organization (UHERO) released May 26.
The research examined how invasive species such as albizia and miconia affect flooding in the Makiki, Mānoa and Pālolo watersheds. Researchers found that unmanaged spread of the invasive plants over the next decade could nearly double expected annual flood damages from $68 million to $134 million.
The study was released following the March 23 flash flooding in Mānoa that overtopped Woodlawn Bridge, flooded homes and left mud across parts of the valley, including Noelani Elementary School. Researchers said healthy native forests act like a natural sponge by slowing stormwater runoff and stabilizing steep slopes. Invasive species can weaken those protections by increasing erosion and clogging streams with fallen trees and debris.
The research team combined hydrological monitoring data with land cover and economic modeling to measure the impacts of watershed management efforts led by the Koʻolau Mountains Watershed Partnership and the Oʻahu Invasive Species Committee.
"The results show decreased streamflow for a given rainfall amount in Makiki and Mānoa, where albizia and miconia were detected and removed most often," the authors wrote, noting that runoff reductions were observed within just a few years of invasive species removal.
The study also projected that unchecked invasive species growth would more than double annual Ala Wai Canal dredging costs from about $1.4 million to $3 million because of increased sediment runoff. Researchers said the findings highlight the need for long-term funding to support watershed protection and invasive species management programs across Hawaiʻi.
Read the entire report on UHERO's website .
UHERO is housed in UH Mānoa's College of Social Sciences .
The post Native forests could help protect Honolulu from flooding first appeared on University of Hawaiʻi System News .
