A water reservoir is constructed by impounding water within a defined area using a dam or excavation, utilizing various materials like rock, earth, concrete, or composites depending on the size and geological conditions.
Constructing a water reservoir is a multi-stage process involving site selection, design, material selection, and construction techniques. Here's a breakdown:
1. Site Selection and Investigation
- Topography: The site should ideally be a natural basin or valley that can efficiently hold water.
- Geology: Thorough geological investigations are crucial to assess the soil's permeability, stability, and load-bearing capacity. This includes soil testing, rock analysis, and seismic studies. Identifying potential fault lines or unstable ground is essential.
- Hydrology: Analyzing the water source (river, stream, rainfall) to determine the reservoir's inflow, outflow, and storage capacity is critical.
- Environmental Impact: Environmental impact assessments (EIAs) are performed to evaluate the potential effects on the surrounding ecosystem, including water quality, wildlife habitats, and downstream flows.
- Land Use: Considerations are given to existing land use, population displacement (if any), and resettlement plans.
2. Design
- Dam Design (if applicable): If a dam is required to impound the water, its design depends on the site's characteristics, water volume, and expected loads. Dams can be:
- Earth Dams: Constructed from compacted soil. They require a watertight core (clay or concrete) or facing (concrete) to prevent seepage.
- Rock-fill Dams: Constructed from rock fragments and require an impermeable membrane on the upstream face.
- Concrete Dams: Offer high strength and stability and can be gravity dams (relying on their weight for stability), arch dams (curved to transfer the load to the abutments), or buttress dams (supported by buttresses).
- Excavation (for open reservoirs): For smaller reservoirs, excavation may be sufficient. The excavation must be carefully designed to ensure slope stability and prevent collapse.
- Spillway Design: A spillway is crucial to safely discharge excess water during floods and prevent overtopping of the dam or reservoir banks. Spillways are designed based on hydrological data and flood frequency analysis.
- Intake Structure Design: The intake structure allows controlled release of water from the reservoir for various purposes (irrigation, water supply, power generation).
- Embankment Design (for open reservoirs): Earthen embankments, crucial for open reservoirs, demand a watertight concrete face or a core of clay or concrete for integrity.
3. Material Selection
The choice of construction materials depends on several factors:
- Availability: Locally available materials can significantly reduce construction costs.
- Cost: The cost of materials plays a crucial role in the overall project budget.
- Durability: Materials must be durable enough to withstand the harsh environmental conditions and the constant pressure of water.
- Strength: Materials must possess sufficient strength to support the water load and resist erosion.
- Impermeability: Impermeable materials are required to prevent water seepage.
| Material | Application | Advantages | Disadvantages |
|---|---|---|---|
| Earth | Earth Dams, Embankments | Low cost, readily available | Susceptible to erosion, requires a watertight core or facing |
| Rock | Rock-fill Dams | High strength, good drainage | Requires an impermeable membrane |
| Concrete | Concrete Dams, Spillways, Cores/Facings for Earth Dams, Intake Structures, lining | High strength, durable, impermeable | High cost, requires skilled labor |
| Composites | Linings, Geomembranes | Lightweight, flexible, impermeable | Can be expensive, requires specialized installation |
| Clay | Core of earth dams and embankments | Relatively impermeable if properly compacted, low cost | Can be erodible, difficult to work with in wet conditions |
4. Construction Techniques
- Excavation: Clearing the site, removing topsoil, and excavating to the required depth.
- Dam Construction: Building the dam layer by layer, compacting each layer to achieve the desired density and stability.
- Embankment Construction: Similar to dam construction, embankments are built in layers and compacted.
- Concrete Placement: Pouring and curing concrete for dam structures, spillways, and intake structures.
- Lining: Applying a lining (concrete, geomembrane, or clay) to the reservoir basin to prevent seepage.
- Installation of Equipment: Installing gates, valves, pumps, and other equipment for water control and distribution.
5. Quality Control and Monitoring
- Material Testing: Regularly testing the properties of construction materials to ensure they meet the required specifications.
- Compaction Control: Ensuring proper compaction of soil layers to achieve the required density and stability.
- Leakage Testing: Testing the reservoir for leaks after construction to ensure water tightness.
- Instrumentation: Installing instruments to monitor the dam's performance, including settlement gauges, piezometers, and strain gauges.
6. Types of Water Reservoirs
There are typically two main types of water reservoirs:
- Open Impounding Reservoirs: These are created by damming a river or stream. They are open to the atmosphere and can be large in size.
- Closed Reservoirs/Tanks: These are enclosed structures that can be built above ground or underground. They are often used for storing smaller volumes of water and protecting it from contamination.
