E-proceedings of the 38 th IAHR World Congress September 1-6, 2019, Panama City, Panama doi:10.3850/38WC092019-1858 2806 RELATIONSHIP BETWEEN SOLID CONCENTRATION AND BED SLOPE TO THE BEGINNING OF MOVEMENT IN WATER-SOIL MIX LEONARDO CASTILLO N. (1) , JUAN CABRERA C. (2) , ROGER HIDALGO G. (3) & FERNANDO HUANCA (4) (1,2,3,4) Facultad de Ingeniería Civil, Universidad Nacional de Ingenieria, Lima, Peru, leonardocastillo@uni.edu.pe (2) Grupo de Investigación en Hidroclimatología y Riesgos Asociados juancabrera@uni.edu.pe (3,4) Instituto para la Mitigación de los Efectos del Fenómeno El Niño rhidalgo@uni.edu.pe ABSTRACT Hydrographically, Peru is divided into two large drainages areas: western, which drains its waters to the Pacific Ocean, and eastern, which drains to the Atlantic Ocean. The first one is characterized by semi-arid highlands and an arid coastal band, with few permanent rivers and a large number of ephemeral streams which are activated only in the wet period. The second one is characterized by a tropical climate, with high precipitations and permanent rivers. Semi-arid characteristic is one factor by the occurrence of the natural phenomena that recurrently affect the western Andes of Peru: the occurrence of debris flow, usually known as "huaycos". Huaycos occurs when high-intensity rains fall on a creek causing soil saturation, failure and consequently flow. These phenomena are common throughout the western Andes of Peru however, in recent years, they begin to manifest more frequently in the eastern Andes as a consequence of deforestation processes. This article presents the study of the initial conditions of the movement for different concentrations of solids of a water-soil mixture at different inclinations in a rectangular steep channel. For this purpose, a channel of 4m length and cross-section of 0.33x0.40m was designed and built, which allows reaching slopes of up to 60% slope. The experimental protocol includes defining an initial water-soil mixture with a weight solid concentration (Cwi), which is placed in the channel and next to modify the slope until it reaches flow. The reiteration of the experiment allows obtaining a set of points and evaluating a possible empirical relationship between variables. The final result shows a logarithmic relationship between variables. This article is the first advance of much broader development research that aims to improve knowledge of the "huayco" phenomenon for its subsequent application in management and control and mitigation measures. Keywords: Steep channel, mudflow, debris flow, initial slope failure 1 INTRODUCTION In Peru, the main debris flows or landslides occur in gullies of regular slope where it is observed that the wave flow (water-soil mixture) circulates over a course or stretch of gorge downstream until be settled in a dejection cone. The present article considers a simplification of said real scene through a diagram of metal channel (of variable slope) and deposition platform (with horizontal slope) according to Figure 1. Hence, this research allows us to test and know more about one of the processes of movement initiation of a water-soil mixture for different channel slopes, where the hypothesis assumed for the movement initiation is the fracture mechanism of the soil in a leaning slope, with an energy increase due to the ground slope and water adding reaching a flow of water-soil mixture. The objectives of the present study include the following: (a) Evaluate the process of movement initiation through water-soil mixture to different slopes in controlled conditions. Tests were realized in a variable slope channel and using a natural ground soil. (b) Establish an empirical relationship between channel slope and sediment concentration by weight for movement initiation. 2 THEORY MODEL Johan C. Winterwerp, et.al (1988) did experiments at gentle slopes, the velocity of a hyperconcentrated sand-water mixtures flow is small, and sediments occurs. Also, the equilibrium slope is a function of specific density, mean sand concentration and the dynamic angles of internal friction (grain size), and not of flow rate.