Hydropower and Headrace Tunnels in Nepal, with Lengths and Sections

• 9entries listed
• 7.47 kmlongest bore
• 44.18 kmtotal length

The record table

How this archive measures: lengths, bores, dates and ordering

How this table is compiled

Further down the table, Intake tunnel of Kulejhani-II is recorded at 5.85 km and Headrace for Chilime at 3.4 km. Only 4 of the 8 rows carry anything in the 14 m 2 column, so that field describes a minority of this table and the rest of the rows are recorded without it.

The median entry measures 5.85 km, so half the table sits below that and half above, which is a better guide to the typical structure here than the headline figure. The shortest recorded entry is 2.4 km against 7.47 km at the top, a spread of 3.11x across the same table.

The middle half of the table runs from 2.85 km to 6.72 km, and that band is where most of the engineering on this page actually sits. Between the longest and the tenth-longest the drop is 5.07 km, which is the part of the table that changes when a single scheme opens.

Where one of these 9 lengths disagrees with an operator's own figure for Nepal, the table keeps the published value and notes the difference instead of averaging the two. The longest entry is 3.1 times the shortest and 1.3 times the median, which is the quickest measure of how uneven the table is.

The entries sum to roughly 44.18 km of bore, an average of about 4.91 km each, though that average describes no actual row. The three longest entries alone account for 20.91 km of the 44.18 km on this page, which is 47 per cent of the total from 3 of 9 rows.

Reading the figures

A new scheme in Nepal would have to beat 7.47 km to change the head of this table, and that is the figure worth rechecking when one opens. The 9 rows for Nepal are ordered by length, not by date, so the most recent opening sits well down the table without being any less current.

4 of the 9 entries fall within a quarter of the median length, which is how tightly this particular list clusters around its typical structure. Eighth on the list is Headrace tunnel for Andhaikhola at 2.4 km, which is where the table stops being about record holders and starts being about ordinary infrastructure.

The table on this page runs to 8 rows and records Headrace for Khimti I, 7 466 m and 14 m 2 for each of them, which is the shape the original compiler chose rather than one imposed here. Tunnel building in Nepal is shaped by geology and settlement pattern as much as by transport policy.

The longest entry is Headrace for Khimti I, at 7.47 km. Read down the 7 466 m column, the 8 values run from 2 400 m to 7 117 m with a midpoint at 4 624 m; the spread rather than the maximum is what says how uneven this set is.

A tunnel list for Nepal reads differently from a neighbouring country's: 7 of these 9 structures pass three kilometres, and the same journey time is bought with one long bore in one country and a dozen short ones in another. Toll plazas sit outside portals rather than inside them, for ventilation reasons as much as for traffic ones.