Micro hydropower, typically defined as installations with a capacity of less than 500 kW, offers a proven, low-cost, and environmentally benign solution for rural electrification. Among the various MHP configurations, diversion or run-of-river (RoR) schemes are particularly attractive for remote mountainous regions. In such systems, water is diverted from a river through a minor intake without establishing a substantial reservoir, requiring minimal to no water impoundment and enabling rapid construction at reduced costs while alleviating issues such as flooding, silt buildup, and social disruption.
However, numerous micro hydro installations have failed due to factors such as poor site selection and uneconomical design. Before selecting any site for development, comprehensive hydrological, geological, and topographical investigations are essential. This article synthesizes current knowledge on site selection criteria for micro diversion hydropower schemes, providing a practical framework for engineers, planners, and community stakeholders.
The fundamental prerequisite for any MHP scheme is the availability of adequate and reliable stream flow. In hilly or mountainous regions, site selection typically involves identifying streams that exhibit constant hydrological flow throughout the year. The installed capacity is conventionally calculated on the basis of flow duration; for mini-hydro plants, a six-month exceedance criteria is often applied, while micro-hydro systems may use 11-month flow data.
Hydrological assessment must account for seasonal variability. RoR plants have a notable limitation in their incapacity to mitigate seasonal flow variability, resulting in power output that closely follows streamflow fluctuations. Therefore, flow duration curves must be developed from either gauged records or, in data-scarce regions, through hydrological modeling.
Recent research has employed the Hydrologic Engineering Center’s Hydrologic Modelling System (HEC-HMS) integrated with GIS to estimate natural power available from river discharge. Remote sensing data, particularly the Shuttle Radar Topography Mission Digital Elevation Model (SRTM DEM), can be utilized to calculate discharge at potential MHP locations.
Environmental flow requirements must be considered. A reserved flow—the minimum flow that must remain in the river to sustain aquatic ecosystems—must be subtracted from the total available flow when calculating exploitable flow. This reserved flow affects the overall energy production and must be determined in consultation with environmental regulations and local stakeholders.
Topographical and Head Assessment
Hydraulic head is the second critical parameter, alongside flow, in determining power output. Power is calculated using the fundamental equation:
Power (kW) = 9.81 × Discharge (m³/s) × Head (m) × Efficiency
A site should have at least 5 meters of head for economically viable micro-hydro development. Head can be determined through various survey methods including altimeters, GPS, dumpy levels, total stations, and water-filled tubes. Field surveys using GPS-based elevation measurements provide practical head estimates.
The terrain surrounding the stream must be suitable for running a length of pipe from the proposed intake structure to the powerhouse location. Key topographical considerations include:
Narrow valleys are preferred for intake structures
Bends in the river should be avoided at intake locations
Flatter land is desirable for desilting tanks, channels, forebays, and powerhouse locations
Stable slopes must be confirmed to avoid landslides
Recent methodological advances have incorporated the effect of hillslope topography on the optimal layout of infrastructure. GIS-based analysis using neighborhood statistical methods can calculate head and identify optimal layouts.
Geological and Geotechnical Considerations
Geological conditions are essential for MHP development planning. The ideal area is one containing good potential head and hard rock formations, such as granodiorite, which provide stable foundations. Geological analysis must assess:
Lithology through surface mapping
Soil filtration stability, particularly gravel soils
Susceptibility to internal suffusion affecting hydraulic structure stability
Sites must be evaluated for geological hazards. Optimal sites exhibit reduced susceptibility to floods and landslides. Specific considerations include:
No active landslide zones in the vicinity
Banks must be stable
Intake should be situated above the 20-year flood elevation
Geological hazard risk assessment, particularly for floods and landslides, should be integral to the site selection process.
Intake and Diversion Structure Siting
The diversion works for a micro-hydropower scheme control the flow of water from the source river into the headrace. The intake location must be chosen to:Minimize bed load entry: The largest possible portion of bed load should remain in the river and not be diverted
Minimize head loss in the intake structure
Minimize debris entry, including floating materials such as ice, timber, and leaves
Avoid narrowing the cross-section of flow
Weir Design Considerations
New intake weirs should be sited in reaches with a steep stream bed gradient and have a low crest height relative to the upstream level of the natural stream bed. They should be sited on or immediately downstream of natural steps, cascades, or falls in the river channel.
Construction of high and permanent weirs (larger than 1–2 m) across the total width of the river is generally undesirable, as damming can cause rapid sediment deposition and change the river course, potentially leaving the intake dry and useless. The weir height should be as low as possible while still maintaining the required water level.
Post time: Aug-31-2026
