ESTIMATING WILDFIRE BEHAVIOUR IN MANGROVE VEGETATIONS

AUTHOR: AZAKA ONYEMAZUWA ANDREW

DEPARTMENT: MECHANICAL ENGINEERING

AFFILIATION: NNAMDI AZIKIWE UNIVERSITY, AWKA

The purpose of this research work is to estimate wildfire behaviour in mangrove vegetations. Southern Nigerian Mangrove vegetations were studied. Allometric equations for estimating the above ground biomass for the three Rhiziphora species in the study area were developed. The equations could aid in estimating the available combustible fuels in the mangrove vegetation during wildfires. A chart and a block model for easy comprehension of carbon dynamics and the pyrolytic steps in a mangrove vegetation fires were also developed. To quantify mangrove fuels based on mass of vapourization , pyrolysis and char formations, an ordinary differential equations (ODE) format was used to mathematically express the models for mass balance for moisture content (MVAP), mass balance of dry materials (MPYR) and mass balance for char, ash, and soot formations(MCHAR). The energy balance equations for the surface and crown rate of spreads were expressed in the differential and integral forms. After critically observing the nature of mangrove fires and its spreading mechanism, it was observed to be characterized with the surface and crown fire types with active crown rate of spread and high fireline intensity. To properly estimate wildfire spread patterns in this vegetation, Nomographs for fuel models 4 and 5 were used because they exhibit same characteristics with southern Nigerian mangrove vegetations. From the Nomograph’s estimations, rate of spreads were estimated to be 108chains/h (36.2124m/min) for fuel model 4 low and high windspeeds, while for fuel model 5 low and high windspeeds, rate of spread was estimated to be 29chains/h (9.7237m/min) and 50.5chains/h (16.93265m/min). The fireline intensities were estimated to 12500btu/min/ft2 (1186.875KJ/min/m2) and 3000btu/min/ft2 (284KJ/min/ m2) for fuel model 4 and 5, with varying flame lengths of 23ft (7m), 29ft (8.7m) and 7ft (2.1m), 9ft (2.7m) for same fuel models respectively. Finally a pictorial approach for estimating burnt area and perimeter was presented, and also used BEHAVEPLUS 5.0.5 to estimate critical surface intensity as 144btu/ft/s (9,115.2KJ/ft/min), crown rate of spread as 29.6chains/h (9.92488m/min) and critical crown rate of spread as 11.2chains/h (3.75336m/min) for both fuel models 4 and 5, while the fire intensity was 22147btu/ft/s (420571.53KJ/m/min) and 1904btu/ft/s (36156.96KJ/m/min), Rate of spread was 434.1chains/h (145.55373m/min) and 149.3chains/h (50.06029m/min), maximum flame lengths were 44.9ft (13.47m) and 14.5ft (4.35m), transition ratio was 447.76 and 38.5, and critical surface flame length varying between 2.7ft (0.81m) – 4.4ft (1.32m) for fuel models 4 and 5 respectively.

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