The construction of irrigation projects, such as dams, barrages, and weirs, requires meticulous planning and execution. At the heart of this process is surveying, a critical step to assess the necessity and feasibility of such structures. Surveying helps determine whether an irrigation project will provide substantial benefits to the area, ensuring that resources are allocated effectively
Steps Involved in Surveying for Irrigation Projects
Surveying for an irrigation project follows a structured sequence of steps to ensure thorough analysis and precise planning. These include examining water availability, analyzing topography, selecting a construction site, and conducting various surveys to refine alignment and finalize the project plan.
Examine Availability of Water
Water availability is the cornerstone of any irrigation project. Before construction begins, it is essential to evaluate the presence and reliability of water sources. This involves:
- Determining whether the river in the area is perennial (flowing year-round) or inundation type (dependent on seasonal rainfall).
- Assessing the river’s discharge history to ensure it meets the area’s irrigation requirements.
- Confirming the availability of a suitable site to construct the irrigation structure.
Examine Topography
Topographic maps play a crucial role in understanding the geographical and agricultural characteristics of the area. These maps are particularly useful in marking tentative canal alignments and evaluating how the irrigation project might interact with existing agricultural lands.
Selection of Construction Site
Once sufficient water is identified, the next step is selecting a site for construction. This involves:
- Conducting soil surveys through boring and pile testing to determine foundation depth.
- Ensuring the site has a sufficient basin area to meet water storage and demand needs.
- Selecting a location with good accessibility for materials and labor.
- Avoiding submergence of valuable lands and ensuring that the canal maintains an allowable bed slope.
River Gauging
River gauging involves measuring water discharge at the selected site to gather essential hydrological data. This includes:
- Recording the river’s daily and yearly discharge levels.
- Documenting the High Flood Level (HFL) and Lowest Water Level (LWL) using historical data.
- Conducting silt analysis to assess sediment levels and their impact on the riverbed.
Marking of CCM (Cultivable Command Area)
The Cultivable Command Area (CCM) refers to land fit for cultivation within the irrigation project’s scope. During surveying, this area is clearly marked on topographic maps to ensure that construction activities do not damage cultivable land. Additionally, CCM data helps estimate the water demand for the project.
Marking of Tentative Alignment
Tentative canal alignments are selected and marked on contour maps following careful analysis. The process considers:
- Covering the entire area intended for irrigation.
- Minimizing earthwork costs associated with cutting and filling.
- Avoiding valuable agricultural lands, religious sites, and other sensitive areas.
- Ensuring canals cross roads, rivers, and railways perpendicularly for efficient design.
Reconnaissance Survey
This survey refines the tentative alignment and identifies potential challenges. Key tasks include:
- Assessing ground slope along the alignment.
- Eliminating alignments that pass through sensitive areas, unless unavoidable.
- Evaluating the nature of the ground within 100 meters on both sides of the alignment.
- Recording past flood events and identifying the need for cross drainage works.
- Ensuring river crossings occur at the shortest width.
Preliminary Survey
After the reconnaissance survey, a detailed preliminary survey is conducted. Key steps include:
- Constructing pillars to mark the centerline of the irrigation project and headworks.
- Conducting boring to determine foundation depth.
- Establishing permanent benchmarks and linking them to the nearby GTS benchmarks.
- Using leveling and survey techniques to prepare detailed maps.
- Recording cross-sectional details of rivers upstream and downstream.
- Estimating earthwork costs and preparing compensation plans for land acquisition.
Final Location Survey
The final location survey ensures the most economical alignment is selected. The steps include:
- Marking the final alignment with centerline pillars and pegs.
- Defining the width of the alignment and marking branch canal locations.
- Finalizing the list of properties eligible for compensation.
Final Survey Report
The last step in the surveying process is preparing a comprehensive report to submit for project approval. The report includes:
- Introduction: An overview of the project.
- Justification: Explanation of the necessity of the project and the chosen alignment.
- Estimates and Specifications: Detailed costs for earthworks, headworks, and land compensation.
- Project Benefits: The expected advantages of the project.
- Recommendations: Suggestions for approval.
Accompanying the report are essential maps and drawings, such as general maps, route survey maps, longitudinal and cross-section drawings, and contour maps of the alignment.
Conclusion
Surveying is a vital step in the successful execution of any irrigation project. By systematically analyzing water availability, topography, and construction feasibility, and by conducting detailed surveys, project planners ensure that irrigation structures are efficient, economical, and beneficial to the target area. Comprehensive surveying sets the foundation for projects that enhance agricultural productivity and water management.