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RoR layout: pressure tunnel and free surface

Short answer

Pressure tunnel layout: weir/intake, desander, pressure tunnel, surge tank, penstock, powerhouse; safe from landslides, for steep valleys. Free surface flow layout: weir/intake, desander, open canal (slope ~1:1000), forebay, penstock, powerhouse; cheaper, needs gentle terrain and cross-drainage works.

Draw a layout (plan and section) of a ROR hydro project for the following cases: (i) alignment with pressure tunnel, (ii) with free surface flow. Name the salient features also (draw with representative contours).

(i) Alignment with pressure tunnel

Plan (contours 1000-1400 m)
        ____________
 ~~ River ~~ Weir/Intake/Desander
              \
               \== Headrace tunnel ===+ Surge tank
                                      |
                              Penstock (steep)
                                      |
                                  PH -> Tailrace -> River
Section
 FSL
  ~~|intake|=============== HGL =======(ST)
                      tunnel             \ penstock
                                          \__PH

Salient features: Weir/barrage, intake with trash rack and gate, gravel trap, settling basin, headrace pressure tunnel (circular, lined), surge tank, penstock (steel, surface or buried), powerhouse (surface or underground), switchyard, tailrace and transmission line. The tunnel flows full under pressure; HGL stays above the crown. Shorter than the canal, safe from slides, used in steep valleys.

(ii) Alignment with free-surface flow

Plan
 ~~ River ~~ Weir/Intake/Desander
                 \_______ Open canal / free-flow tunnel
                         \______ Forebay
                                   \ Penstock
                                    PH -> River
Section
 ___weir__intake___ canal (S = 1:1000)______forebay
                                              \ penstock
                                               \_PH

Salient features: Weir, intake, desander, free flow canal (or tunnel flowing partly full with slope 1:1000), spillway at forebay, forebay with trash rack, penstock, powerhouse and tailrace. Cheaper, but the head is lost to the slope, and the canal needs bends and cross-drainage works; needs gentle terrain.

✓ Answer checked by Claude Opus 5.5 (high effort)

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