The processof sedimentation and sediment transportin estuaries consists of the processes of settling, wearing away of the estuary river bed, and carrying away sediment. Hydrophysical studies of the processes of sedimentation and bed erosion for the Kuala Jengki Manado river estuary may be based on the distribution of position and time of the flow velocity variable. Analysis of the variable and its change along the river estuary can indicate the process of erosion or sedimentation that occurs at the estuary. The relationship between the two hydrophysical conditions of bed erosion and river bed material sedimentation is determined by hydrological parameters as well as theparticle diameter, flow velocity, particle type, gravitational force, and slope of the riverbed. These hydrological parameters will result in the critical value of bed erosion and sedimentation as well as the evaluation of the potential for erosion and sedimentation along the Kuala Jengki Manado estuary.

The utilized method to determine the data for hydrological parameters was the development of the “sediment rating curve”. Measurement of flow speed was conducted at a position within 4 to 6 cm above the river bed, which allows it to be conducted without disrupting the river bed material. The flow speed as measured on the layer closest to the surface of the river bed (v₀) varied between 29,0 cm sec^-1 and 41,4 cm sec^-1. The highest value for bed stream velocity (v₀) (41.4 cm sec^-1 - 0.414 m sec^-1) was higher than the lowest critical value (0.094175 m sec^-1), and thus for the evaluation of potential, all segments of measurement indicate occurring riverbed surface erosion.

The sedimentation critical value had a critical value ratio (CVR) of (m) = 1.1. For depth variations from 0.78 m to 1.98 m, the obtained range for sedimentation critical value was from 0.5161 m sec^-1 to 0.9367 m sec^-1. The highest critical value (v₀) was 0.414 m sec^-1, which is less than the sedimentation critical value (0.5161 m sec^-1) and thus for the evaluation of potential, the measurement location at distances from 0 m to 1300 m comprises an area for bed load sedimentation.

Keywords: Critical Value, Potential,Erosion,Sedimentation,Estuary.