Satellite-Town Density and Infrastructure Phasing Along a Metro Corridor
A peri-urban planning area of 200 ha is proposed as a satellite settlement along a new metro corridor. The plan proposes 25,000 dwelling units over 10 years, with a gross density of 125 dwellings per hectare. Existing water supply is 15 MLD, sewage treatment capacity 10 MLD, and the only access road is a two-lane carriageway. The projected population is 100,000 at 4 persons per dwelling unit. The local authority wants to approve the layout in one phase to attract investment. Farmers’ groups object to land acquisition. The metro station is at the southern edge, and a seasonal stream crosses the northern parcel. There is no stormwater drain in the existing village. The planning team must recommend a phasing and infrastructure strategy that is financially and environmentally defensible.
1. Test whether the proposed density and population are consistent with the stated infrastructure capacities. Show the per-capita demand assumptions you use and identify the binding constraint.
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Use standard planning assumptions: 135 litres per capita per day (lpcd) for water and 80% of water demand returning as sewage. Population = 25,000 DU × 4 = 100,000. Water demand = 100,000 × 135 = 13.5 MLD. Sewage flow = 0.8 × 13.5 = 10.8 MLD. Existing water supply is 15 MLD, so water has a small margin. Existing sewage treatment is 10 MLD, so the sewage flow of 10.8 MLD exceeds capacity by 0.8 MLD at full build-out. The binding constraint is therefore sewage treatment, not water. The two-lane access road is also likely insufficient: 100,000 residents generate several thousand peak-hour trips, and a two-lane carriageway typically carries only 15,000–20,000 PCU per day. The density of 125 du/ha is high but not inherently unsustainable if infrastructure is upgraded and open space is protected. The recommendation should not be to reject the density outright but to make approval conditional on staged sewage and road upgrades, with the first phase capped below the 10 MLD sewage limit.
2. Recommend a phased development sequence with infrastructure triggers. Explain how you would sequence land acquisition and metro-oriented development.
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Phase 1 should be the southern parcel within 800 m of the metro station: about 8,000 DU (32,000 persons) on 60–70 ha. At 135 lpcd this needs 4.3 MLD water and 3.5 MLD sewage, which fits existing capacity. Trigger for Phase 2: sewage treatment upgraded to at least 15 MLD, water to 20 MLD, and the access road widened to four lanes with a dedicated bus lane. Phase 2 can add 10,000 DU in the middle parcel. Phase 3, the northern parcel near the stream, only after stormwater and floodplain studies are approved. Land acquisition should use land pooling or readjustment rather than outright purchase: farmers contribute land and receive a share of serviced plots, which reduces resistance and shares development value. Metro-oriented development means higher density and mixed use within 500 m of the station, stepping down beyond 800 m. Infrastructure must be commissioned before occupancy certificates, not after. This sequencing protects the authority from approving 100,000 people on 10 MLD of sewage capacity.
3. Identify two environmental risks from the stream and stormwater and propose planning controls that do not rely on major grey infrastructure.
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Risk 1: the seasonal stream floods the northern parcel during monsoons, and new impervious surfaces increase peak runoff downstream. Risk 2: without a stormwater drain, untreated runoff from roads and plots can contaminate the stream and stagnate in low-lying areas. Controls should be distributed and green: (a) a no-build floodplain setback along the stream, with the setback used as a park and infiltration zone; (b) bioswales and vegetated swales along roads to slow and filter runoff; (c) permeable paving in parking and pedestrian areas; (d) detention ponds or retention basins at the low end of each phase, sized for the post-development runoff; (e) rooftop rainwater harvesting and recharge pits; (f) preserving existing village ponds and drainage channels instead of piping them. These measures reduce peak flow and pollutant load without a large concrete drain. They also create public space. The planning approval should require a site-specific stormwater plan and a maintenance budget before Phase 3 begins.