Band-e Darreh South Extension Dam (Birjand Darreh South Gravity Dam)
Darreh South Dam · Birjand South Extension
Khwarazmian Late Islamic 1210 CE (Birjand)·Khwarazmian South Khorasan Birjand oasis·🇮🇷 South Khorasan Province, Birjand County, Band-e Darreh gorge south branch (Bagh-e Sarhangi south), Iran
About
About Band-e Darreh South Extension Dam (Birjand Darreh South Gravity Dam)
South branch gravity-arch dam (1,520 m) 1.2 km south of classic Band-e Darreh (Bagh-e Sarhangi) gorge north dam, Birjand County, South Khorasan. Arch-gravity dam 42 m long, 18.2 m high, 3.5 m crest thickness with upstream convex 8 m radius and downstream stepped buttress 2-tier, trapping 28,000 m³ from Darreh seasonal wadi + qanat feed. Supplies Bagh-e Sarhangi southern terraces 16 ha via 820 m stone canal with distribution cistern 8-m diam. Dated Khwarazmian 1210 CE with 1980s repair retaining Khwarazmian ashlar 70%. Uniquely uses wadi+qanat conjunctive — qanat mouth inside reservoir at dam foot feeding year-round. Threat: Birjand urban expansion and Darreh gorge quarrying for ashlar.
Why it mattersOnly conjunctive wadi+qanat dam in Iran — qanat mouth inside reservoir year-round supply with seasonal wadi bulk.
Open questions
Mysteries & theories
Mysteries
- 01Why conjunctive 1210 CE — qanat insufficient vs wadi flash
Theories
- 01Khwarazmian conjunctive as resilience to flash-drought coupling
Theories are interpretations, not findings. The seal above tells you how much scholarly weight the place carries.
History
How it came to be
- Built
- c.1210 CE (Khwarazmian)
- Period
- Khwarazmian Late Islamic 1210 CE (Birjand)
- Culture
- Khwarazmian South Khorasan Birjand oasis
- Builders
- Khwarazmian Birjand gorge engineers
- Purpose
- South gorge arch-gravity 42 m 18.2 m conjunctive wadi 28,000 m³ + qanat supply to southern Bagh-e Sarhangi terraces 16 ha
- Abandoned
- still operating storage seasonal + qanat year-round
- Rediscovered
- 2009 South Khorasan hydraulic survey; 2018 canal cistern mapping
- Excavation
- Excavation ongoing
1210 CE
Khwarazmian south branch 42 m 8 m arch 18.2 m
1980
Repair retains 70% Khwarazmian ashlar
2009
Birjand gorge south branch hydraulic survey
On the ground
Structures & features
32.7500° N · 59.1200° E · 1520 m · 2 mapped features
Arch-Gravity Embankment (42 m × 18.2 m)
dam42-m arch-gravity 8 m radius upstream convex with downstream 2-tier buttress
32.7510° N · 59.1210° EDistribution Cistern (8 m diam)
structure8-m diam stone distribution cistern at canal 820 m terminus
32.7520° N · 59.1230° E