Using Topographic Wetness Index and Stream Power Index to Identify Pluvial Flood Points Areas in Mariposa County, California

Abstract:

Pluvial flooding events are responsible for damaging natural landscapes and urban areas. Floods such as these are independent of flowing water sources like rivers and streams, rather depending on the landscape’s topography with intensity and duration of rainfall. Mariposa county, located in California’s central valley, a region dominated by mountains and valleys varying in size, is susceptible to pluvial flooding. Determining areas with a high probability of flood occurrence is achievable through flood susceptibility mapping. However, for this study, the use of efficient topographically dependent models such as the TWI [Terrain Wetness Index] and SPI [Stream Power Index] was used to determine what towns of Mariposa are likely to suffer from pluvial flooding, identifying which segments of channels flowing through the county are likely to form gullies, and presenting areas of undeveloped land which should remain undeveloped for possible damages from inundation. Other components used such as Flow Direction used in identifying the downslope direction of land, while slope modeling proves whether an area of interest resides within a valley or plain. Lower Yosemite Valley is home to the largest and most intense saturated zones in Mariposa. According to the TWI, the area surrounding the Southern Chowchilla river and its tributaries are highly susceptible to high accumulation. A significant part of Mariposa County can be considered unbuildable as the indexes produced for this region reveals that many catchment areas (or river channels) are of high saturation capability.

Keywords: Keywords: Flood, Urban Areas, Mariposa County, TWI, SPI

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