Turbidity Currents on Steep Slopes: Application of an Avalanche-type Numeric Model for Ocean Thermal Energy Conversion Design

Absln~--To minimize cold water pipe lengths, the most favorable land or fixed platform based Ocean Thermal Energy Conversions (OTEC) sites have subbottom slopes greater than 5 °. Observations at OTEC sites in Hawaii indicate that turbidity currents of an impulsive or episodic nature can occur with frontal speeds of several meters'per second. Such speeds and the attendant potential for sediment transport and abrasion along routes containing OTEC installations indicate that the pertinent features of these flows are an important design criteria for OTEC or any other steep-slope marine installation. To satisfy this need, models of oceanic turbidity flows and similar flows have been examined. The model that addresses OTEC steep-slope conditions most succinctly was developed originally by Hopfinger and Tochon-Dangny (1977) for snow avalanches on land. This two-dimensional avalanche model is used to estimate the speed and growth characteristics of potential turbidity currents downslope for various postulated marine conditions of initial flow density, height, volume, and length at slopes from 5 to 60 °. The areas of additional research required to increase reliability of the analyses are in the initiation and initial development of a turbidity plume, the mechanisms of sediment entrainment to and loss from the plume, and three-dimensional in addition to two-dimensional studies.