8.1 INTRODUCTION

This chapter describes the design aspects of hydraulic structures related to the production of hydroelectric power. These structures include headrace channels; intakes; conveyance tunnels; surge tanks; penstocks; penstock manifolds; draft-tube exits; tailtunnels, including tail-tunnel surge tanks and outlets; and tailrace channels. The procedures provided in this chapter are most suitable for developing the preliminary designs of hydraulic structures related to the development of the hydroelectric projects. To finalize designs, detailed studies must be conducted: for example, economic analysis for the determination of penstock diameters, computer modeling of hydraulic transients for surge tank design, and studies of physical models of intake and its approach.

8.2 HEADRACE CHANNEL

An open-channel called the headrace channel or power channel ( canal) is sometimes required to connect a reservoir with a power intake when the geology or topography is not suitable for a tunnel or when an open-channel is more economical. The channel can be lined or unlined, depending on the suitability of the foundation material and the projects economics. Friction factors for various linings used for design are as follows:

Headrace channels are generally designed and sized for a velocity of about 2 m/s (6.6 ft/s) at design flow conditions. Economic considerations may result in some variation from this velocity, depending on actual project...