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<br />CHAPTER II. DEBRIS-FLOW DRAINAGE BASINS <br /> <br />A. Location of Basins <br /> <br />The three debris-flow drainage basins studied aTe indicated on Figure <br /> <br />I and are named Gulch A, Guloh B, and Gulch C. These three basins differ <br /> <br />from one another in size, area, Ilnd volume of availablE! debris on steE!p <br /> <br />slopes; however, their general characteristics in terms of potential for <br /> <br />producing thE! flows arE! similar and are discussed below. <br /> <br />B. General Characteristics of Debris-Ylow Drainage Basins <br /> <br />Solid material is transported downstrE!am in all drainage basins by <br /> <br />running water and other mass-wasting processes. However, progressively <br /> <br />smaller and steeper basins often tend to transport solid material by a <br /> <br />particular combination of floodi.ng and mass-wasting proceSfles. Thi s comb ina t ion) <br /> <br />as described earlier, is called a debds flow "nd is often the most important <br /> <br />erosion process in small drai,nage basins. Debris flows are the dominant <br /> <br />process in the small basins studied here. <br /> <br />In order for debris flows to <br /> <br />occur, certain conditions must be met that include (1) sufl'icient available <br /> <br />unconsolidated debris, including soil, rock, and organic material, (2) <br /> <br />steep slopes, (3) a sufficiently high clay content in the debris, and (4) <br /> <br />a large volume of debris compared with the available water. All of these <br /> <br />necessary conditions exist ill the basins studied here and are discussed <br /> <br />- 6 - <br />