Establishing topographical survey control points is a foundational activity in land surveying that ensures accurate mapping and data collection. In Kenya, where diverse terrains from urban Nairobi to rural highlands present unique challenges, precise control points enable surveyors to maintain spatial integrity throughout a project. This chapter focuses on the tools, equipment, and materials essential for reconnaissance and setting up control points effectively, ensuring that surveyors can work efficiently and safely in various environments.

2.1 Tools, Equipment and Materials for Reconnaissance

Reconnaissance in topographical surveying involves preliminary fieldwork to gather information, identify suitable sites for control points, and prepare for detailed survey operations. The choice of tools and materials directly impacts the accuracy, efficiency, and durability of control points, especially in Kenya’s varied landscapes such as the rocky soils of the Rift Valley or the soft soils in coastal regions.

2.1.1 Hammer

The hammer is a critical tool used primarily for driving markers such as pegs or iron pins into the ground during the establishment of control points.

Types of Hammers Used in Surveying

• Claw Hammer: Commonly used for driving pegs and removing nails; its curved claw allows for extraction of embedded objects.
• Sledgehammer: Utilized for driving larger iron pins or stakes into hard or rocky ground, offering greater force.
• Ball Peen Hammer: Used for shaping or adjusting metal markers on site.

Specifications Relevant to Surveying

• Weight typically ranges between 0.5 kg to 2 kg depending on use.
• Handle length affects leverage and control; wooden or fiberglass handles reduce shock.

Proper Use and Safety

• Ensure a firm grip and controlled swings to avoid injury or damage to markers.
• Use protective gloves and eye protection when striking metal pins or working on rocky terrain.

Maintenance and Care

• Regularly inspect for handle cracks or loose heads.
• Store in dry conditions to prevent rust and handle degradation.

2.1.2 Pegs

Pegs are temporary or semi-permanent markers used to identify and demarcate control points during reconnaissance.

Types of Pegs

• Wooden Pegs: Easily available and inexpensive, suitable for soft soils but less durable.
• Metal Pegs: More durable and visible but prone to rust without treatment.
• Plastic Pegs: Resistant to weathering but less sturdy.

Criteria for Selecting Pegs

• Soil type and hardness: Wooden pegs suit soft soils; metal for rocky grounds.
• Visibility: Brightly painted pegs aid in quick identification during fieldwork.
• Durability: Consider project duration and environmental conditions.

Placement Techniques

• Pegs should be driven firmly into the ground at the exact control point location.
• Position pegs to avoid interference with ongoing activities and ensure they are not easily dislodged.

Assessment for Reusability

• Inspect pegs for damage or wear after each use.
• Replace pegs that show signs of splitting, warping, or corrosion.

2.1.3 Spade

The spade is a versatile digging tool essential for preparing holes to place permanent markers or to clear vegetation around control points.

Spade Types Suitable for Surveying

• Pointed Spade: Ideal for penetrating hard or compacted soils.
• Flat Spade: Useful for cutting roots or leveling soil around markers.
• Trenching Spade: Narrow blade facilitates precise digging for marker placement.

Proper Use in Control Point Establishment

• Used to dig holes for iron pins or to clear debris around markers.
• Enables accurate positioning by allowing firm embedding of markers below the surface.

Maintenance and Handling

• Keep the blade sharp and free from rust to ease digging.
• Clean after use to prevent soil buildup and corrosion.

Safety Considerations

• Use correct posture to avoid back strain.
• Wear protective boots to prevent foot injuries during digging.

2.1.4 Shovel

A shovel complements the spade by enabling the movement of larger volumes of soil or sand during control point preparation.

Differences Between Spade and Shovel

• Shovels typically have a curved blade for scooping and moving soil.
• Spades have a flat blade designed for digging and cutting.

Applications in Survey Control Setup

• Used for excavating larger holes for concrete marker foundations.
• Assists in backfilling around markers using sand or soil.

Specifications and Features

• Blade size and shape vary depending on soil type and task.
• Long handles improve leverage but require careful handling in confined spaces.

Care and Storage

• Clean after use to prevent rust and soil hardening on the blade.
• Store in a dry place to prolong tool life.

2.1.5 Measuring Tape

Measuring tapes are fundamental in reconnaissance for measuring distances between control points and verifying site dimensions.

Accuracy and Calibration

• Steel tapes provide the highest accuracy but require careful handling to avoid kinks.
• Regular calibration against a standard baseline is necessary to maintain precision.

Usage in Reconnaissance

• Used for preliminary measurements to establish rough control point spacing.
• Assists in setting out pegs at specified intervals.

Handling and Maintenance

• Avoid twisting or bending to prevent permanent damage.
• Clean tape after use and rewind carefully to prevent tangling.

Safety in Use

• Keep fingers clear when retracting tapes to avoid cuts.
• Use in pairs for long distances to maintain tension and accuracy.

2.1.6 Ranging Rods

Ranging rods serve as visual markers and aids for aligning points during reconnaissance and survey operations.

Importance in Surveying

• Provide clear visual references to assist in establishing straight lines between control points.
• Used in conjunction with measuring tapes and theodolites for precise alignment.

Selection Criteria

• Visibility: Bright colors improve detectability in dense vegetation or low light.
• Durability: Lightweight materials like aluminum or fiberglass resist corrosion.

Usage Techniques

• Place rods vertically at control points during sighting.
• Coordinate with total station or GNSS receivers for accurate positioning.

Maintenance

• Inspect for bent or broken sections regularly.
• Clean rods to maintain color visibility and structural integrity.

2.1.7 Total Station

The total station is a sophisticated electronic instrument combining an electronic theodolite with an electronic distance meter, critical for precise control point establishment.

Components and Functions

• Electronic Theodolite: Measures horizontal and vertical angles with high precision.
• Electronic Distance Meter (EDM): Measures distances using infrared or laser signals.
• Data Collector: Stores measurements and facilitates data transfer.

Operational Procedures

• Set up on a stable tripod at a known reference point.
• Level the instrument using built-in bubble levels.
• Sight target prisms placed on ranging rods or markers to measure angles and distances.

Advantages in Kenyan Surveying Context

• Enables rapid data collection over large or inaccessible areas such as hills or forested zones.
• Reduces human error compared to manual angle and distance measurements.

Maintenance and Calibration

• Regularly clean lenses and prisms to prevent measurement errors.
• Perform calibration checks according to manufacturer’s guidelines to maintain accuracy.

2.1.8 GNSS Receivers

Global Navigation Satellite System (GNSS) receivers provide geospatial positioning data by receiving signals from satellites, essential for establishing control points with global coordinates.

Types of GNSS Receivers

• Single Frequency: Less expensive, suitable for general reconnaissance with meter-level accuracy.
• Dual Frequency: More precise, used for detailed control point establishment requiring centimeter accuracy.

Applications in Kenyan Terrain

• Ideal for remote or difficult terrain where traditional line-of-sight instruments are impractical.
• Used by county government surveyors for mapping large agricultural estates or infrastructure projects.

Operational Considerations

• Requires clear sky visibility for optimal satellite reception.
• May use base stations or network corrections for enhanced accuracy.

Maintenance and Data Management

• Keep antennas clean and free from obstructions.
• Regularly update firmware and software to maintain compatibility and performance.

2.1.9 Sand

Sand is a common material used in setting control points, particularly for creating stable bedding for markers and concrete bases.

Role in Control Point Stability

• Provides a level and compacted base to prevent marker movement.
• Facilitates drainage around markers, reducing erosion effects.

Quality Characteristics

• Should be clean-free of organic matter and clay to ensure good compaction.
• Grain size affects compaction and stability; medium-grain sand is preferred.

Application Techniques

• Spread sand evenly in the hole before placing markers or iron pins.
• Compact sand layers using hand tampers to achieve firmness.

Sourcing and Environmental Considerations

• Use sand from licensed quarries to avoid environmental degradation.
• Avoid using sand from riverbeds prone to seasonal erosion.

2.1.10 Cement

Cement is used to create durable concrete bases that protect control points from environmental damage and accidental displacement.

Purpose in Survey Control Points

• Provides a solid foundation for iron pins or benchmarks.
• Enhances longevity and visibility of permanent markers.

Types of Cement Suitable for Field Use

• Ordinary Portland Cement (OPC): Commonly used due to availability and strength.
• Rapid Hardening Cement: Useful in projects requiring quick setting times.

Mixing and Application

• Typical mix ratios include 1 part cement, 2 parts sand, 4 parts aggregate.
• Pour concrete into pre-dug holes around markers, ensuring no voids.

Curing and Protection

• Allow concrete to cure for at least 7 days to achieve strength.
• Protect curing concrete from rain and extreme temperatures.

2.1.11 Iron Pin

Iron pins serve as permanent physical markers embedded into the ground to denote precise control points.

Characteristics of Iron Pins

• High tensile strength to resist bending or breaking.
• Corrosion-resistant coatings to prevent rusting in varied Kenyan soils.

Installation Procedures

• Driven into pre-prepared holes filled with sand and concrete for stability.
• Top of the pin is often capped or painted for visibility.

Advantages Over Other Markers

• Longevity and ability to maintain precise location over decades.
• Resistant to accidental damage from human or animal activity.

Maintenance and Verification

• Periodically inspect pins for displacement or corrosion.
• Re-establish or replace pins if disturbed by construction or natural processes.

Chapter Summary

This chapter covered the essential tools, equipment, and materials required for reconnaissance in topographical surveys, including hand tools like hammers and spades, measuring instruments such as tapes and ranging rods, and advanced technology like total stations and GNSS receivers. It emphasized the importance of identifying existing control points to establish a reliable foundation for new surveying work. Criteria for selecting appropriate topographical survey control points were discussed to ensure accuracy and coverage of the survey area. The chapter also explained the process of extending control points to cover larger or adjacent areas as needed for comprehensive mapping. Finally, it detailed the monumenting of control points, highlighting the use of materials like sand, cement, and iron pins to create durable and visible markers that maintain survey integrity over time.