Manipur and the 1% Flood — India Flood Atlas

Manipur is shaped like a bowl. A broad oval valley — the Imphal valley, about a tenth of the state’s area but home to most of its population — sits ringed by hills on every side. Water from those hills drains inward, collects in Loktak Lake, and leaves through a single outlet: the Manipur river, where the Ithai barrage stands.

That geometry produces a flood regime unlike anywhere else in this atlas. And it produces a state that has to be read in two halves, because the atlas finds one district at 72% exposure and the state’s most populous district at 18%.

The scale

Of Manipur’s 1,224,294 building footprints, 218,975 — 17.9% — sit in the modeled 1% annual-chance floodplain. That is a little under the national figure of roughly 20%.
The mean depth over exposed buildings is 2.45 m, but this is a blended figure across two very different terrains and should not be read as typical of anywhere. In the valley the modeled water is under a metre; in the hills the model reports depths that the terrain makes unreliable.
2,975 km of road — 11.0% of the network — is exposed.
25 km of railway — 7.2% — is exposed, on a small network of 342 km.

Where it concentrates

District	% of buildings exposed	Exposed buildings	Modeled depth
Jiribam	72.0%	14,015	6.12 m · uncertain
Imphal East	35.1%	57,588	0.78 m
Imphal West	18.1%	51,028	0.62 m
Chandel	17.0%	6,258	2.55 m
Noney	16.9%	2,780	9.13 m · uncertain
Kakching	16.5%	12,258	0.98 m
Kangpokpi	16.1%	16,066	3.56 m · uncertain
Bishnupur	14.4%	12,698	0.81 m

Jiribam is the outlier, and it is a genuine one. At 72.0%, nearly three buildings in four are in the floodplain — the second-highest district figure anywhere in the Northeast outside Assam. Jiribam is geographically detached from the rest of Manipur: a small lowland enclave in the far west, on the Barak river plain, sharing its hydrology with Assam’s Cachar district rather than with the Imphal valley. When Silchar floods, Jiribam floods.

The Imphal valley districts tell the opposite story. Imphal East (35.1%), Imphal West (18.1%), Kakching (16.5%) and Bishnupur (14.4%) all model water under a metre deep — 0.62 m to 0.98 m. This is the signature of waterlogging, not river flooding: broad, shallow, slow to drain, and concentrated exactly where Manipur’s people and buildings are. Imphal East and Imphal West together account for 108,616 exposed buildings, half the state’s total.

The hill districts — Noney at 9.13 m, Kangpokpi at 3.56 m — carry modeled depths that reflect steep valleys colliding with a ~30 m elevation model rather than plausible water. Their percentages are meaningful; their depths are not.

Why Manipur floods

A closed bowl with one drain. Every river in the valley — the Imphal, Iril, Thoubal, Sekmai, Nambul — converges on Loktak Lake and exits through the Manipur river. A single constricted outlet means water backs up across the valley floor whenever inflow exceeds outflow.
The Ithai barrage. Built as part of the Loktak Hydroelectric Project, which supplies power across the seven Northeastern states, the barrage impounds the Manipur river just below the confluence of the Imphal and Tuitha rivers, south of Loktak. It holds the lake at an artificially high and stable level. That stabilised level is precisely what reduces the valley’s capacity to absorb a flood peak, and it is why the valley’s exposure is broad and shallow rather than confined to riverbanks. The barrage is the single most consequential piece of flood infrastructure in Manipur, and it was not built for flood control.
Deforested, steep hill catchments deliver water to the valley quickly. Runoff that once arrived over days now arrives in hours.
Cyclone remnants reaching this far inland. In May 2024, Cyclone Remal brought rainfall that flooded Imphal East, Imphal West, Kangpokpi, Senapati and Jiribam, breached embankments, overflowed the Sekmai river, and collapsed the Irang Bailey bridge on National Highway 37 — severing the Imphal–Jiribam road. Across the Northeast, Remal killed 39 people. A Bay of Bengal cyclone is now a routine flood driver for a landlocked state.
Urban encroachment on the valley floor. Imphal’s growth has filled in low ground and natural drainage lines, which is why exposure there is measured in buildings rather than in farmland.
Fragile lifelines. Manipur’s connection to the rest of India runs on a small number of highways through steep, landslide-prone terrain. The Irang bridge collapse showed how a single failure isolates the state.

Reading the numbers honestly

The valley depths (0.6–1.0 m) are reliable. Flat terrain is where a 30 m DEM works well, and these figures should be taken at face value.
The hill depths are not. Noney’s 9.13 m and Kangpokpi’s 3.56 m reflect terrain steepness, not water. Read those districts by percentage only.
Jiribam’s 72% is trustworthy; its 6.12 m is not. The extent reflects genuine Barak lowland exposure; the depth is inflated by the surrounding hill edges captured in the same district.
The atlas models riverine flood depth. It does not model barrage operation, which is central to Manipur’s valley hydrology, nor landslides, which are a leading cause of death in the hill districts.
District boundaries follow the 2011-census-derived set (16 districts), which matches Manipur’s current official count.

A strategic approach

Pillar 1 — Revisit how the Ithai barrage is operated. The barrage holds Loktak high for power generation, and that directly reduces the valley’s flood buffer. A seasonal operating rule that draws the lake down ahead of the monsoon would trade a little generation for a lot of flood capacity. This is the highest-leverage change available in Manipur.

Pillar 2 — Treat the Imphal valley as a drainage problem. Sub-metre water across 108,000 buildings is not solved by embankments. It is solved by restoring and maintaining the valley’s natural drainage channels, clearing encroachment on low ground, and stormwater infrastructure in Imphal.

Pillar 3 — Plan Jiribam with Assam, not with Imphal. At 72% exposure, Jiribam is a Barak-valley problem administratively attached to Manipur. Its warning, evacuation and flood-proofing should be coordinated with Cachar.

Pillar 4 — Harden the lifeline routes. NH-37 and NH-2 are the state’s arteries. Bridges designed for scour and debris, with pre-positioned bailey spans, prevent a single failure from cutting Manipur off.

Pillar 5 — Catchment restoration in the hills. Slowing runoff into the valley reduces both the flood peak and the landslide toll, and it is the only intervention that helps the hills and the valley at the same time.

The honest bottom line: Manipur’s 17.9% headline hides two different states. The Imphal valley floods shallow and wide — 0.6 to 1.0 m across more than 100,000 buildings — because it is a bowl whose only drain is held artificially high by the Ithai barrage for hydropower. Jiribam, detached in the west on the Barak plain, floods at 72%, sharing its fate with Silchar rather than with Imphal. The hill districts’ alarming modeled depths are terrain artifacts and should be read as percentages only. Manipur’s most useful flood lever is not a wall or a channel — it is the operating rule of a barrage built for electricity.

Sources

Cyclone Remal, May 2024 — ReliefWeb: Cyclone Remal, North East — Situation Report 4 · Tribune India: Cyclone Remal triggers floods across Manipur · Prokerala: Incessant rain hits normal life, connectivity in Manipur
Loktak and the Ithai barrage — Deccan Herald: Several rivers in Assam, Manipur experience severe flooding (CWC data)
Later events — News on AIR: Flash floods and landslides hit Manipur
Exposure statistics — India Flood Atlas (modeled 100-year / 1% annual-chance event), NEER.

Exposure figures are modeled estimates (~30 m) for a 1% annual-chance flood, intended for awareness and prioritisation — not parcel-level certainty, and least reliable in the steepest terrain. Building footprints are structures, not people.