Locate topographical survey control points is a critical phase in land surveying that establishes reliable reference markers for detailed mapping and data collection. In Kenya, accurate location of these control points ensures that subsequent surveys are consistent and can be integrated with national geospatial frameworks. Surveyors working in diverse environments, from agricultural lands in Rift Valley to urban developments in Nairobi, must utilize appropriate tools and materials during reconnaissance to identify and prepare these points effectively.

2.1 Tools, equipment and topographical survey control points materials for reconnaissance

The reconnaissance stage involves preliminary site visits to identify suitable locations for control points and to prepare the ground for precise measurements. Surveyors rely on a combination of hand tools, measuring instruments, and durable materials that withstand environmental conditions. The choice of tools and materials directly affects the accuracy and longevity of control points, which in turn influences the quality of the topographical survey.

2.1.1 Hammer

The hammer is a fundamental hand tool used in the physical marking and installation of control points on the ground.

Types of Hammers Used in Surveying

Surveyors commonly use claw hammers and sledgehammers. Claw hammers allow for driving and removing nails or pegs, while sledgehammers provide the force needed to drive iron pins or stakes into hard ground. The choice depends on soil type and the size of the marker.

Role in Installing Control Points

The hammer is essential for embedding markers such as iron pins or wooden pegs firmly into the soil. This ensures that control points remain stable during the survey period, resisting displacement by environmental factors or human activity.

Maintenance and Handling

Maintaining the hammer’s head securely fixed to the handle prevents accidents and inefficiency. Surveyors should regularly inspect the handle for cracks and the head for rust, especially when working in humid regions like Kisumu or coastal areas.

2.1.2 Pegs

Pegs serve as visible ground markers for control points, and their assessment involves selecting appropriate types and materials based on site conditions.

Types of Pegs

Wooden pegs, metal pegs, and plastic pegs are commonly used. Wooden pegs are biodegradable and suitable for short-term surveys, metal pegs offer durability for long-term projects, and plastic pegs provide visibility but less durability.

Criteria for Selecting Pegs

Selection depends on soil type, expected survey duration, and environmental exposure. For example, in rocky terrains like those around Mount Kenya, metal pegs are preferred for their resilience, whereas in agricultural lands, wooden pegs minimize soil disturbance.

Assessment of Peg Stability

Surveyors must evaluate the peg’s ability to resist movement due to weather, animal activity, or human interference. Stability tests may include manual attempts to dislodge the peg and checking for firm embedding below the soil surface.

2.1.3 Spade

The spade is a digging tool used to prepare the ground for installing control points, especially when embedding markers below the surface.

Design and Specifications

Survey spades typically have a flat, rectangular blade with a sturdy handle for leverage. The blade width varies depending on the size of the hole required for the control point material.

Use in Control Point Installation

Spades enable the excavation of holes to set iron pins or concrete-filled markers at precise depths. This ensures markers are less susceptible to being disturbed and can be accurately located during subsequent surveys.

Safety and Maintenance

Proper handling reduces strain and injury risks during excavation. After use, spades should be cleaned to prevent rust and soil buildup, which can degrade the tool’s effectiveness.

2.1.4 Shovel

The shovel complements the spade by facilitating the removal of larger volumes of soil during site preparation for control points.

Differences Between Shovel and Spade

Unlike the spade’s flat blade, the shovel has a curved blade suited for scooping and moving loose soil. This makes it ideal for clearing trenches or larger holes needed for substantial control point foundations.

Application in Topographical Surveys

In surveys requiring concrete bases or heavy markers, shovels assist in creating the necessary excavation. For instance, in flood-prone areas of Western Kenya, control points may need deeper foundations to prevent washout.

Maintenance Practices

Regular blade sharpening and handle inspections extend the shovel’s lifespan. Proper storage prevents moisture-related damage, especially in humid survey environments.

2.1.5 Measuring tape

• Steel tapes provide durability and resistance to stretching, ensuring accuracy over repeated uses.
• Surveyors must keep tapes clean and avoid kinks or twists that can distort measurements.
• When measuring long distances, tapes should be held taut and level to prevent sagging errors.
• Calibration against certified standards is necessary to maintain measurement integrity.
• Protective cases reduce damage during transport across rugged terrains.

2.1.6 Ranging rods

Ranging rods are visual aids used to establish straight survey lines and mark positions during reconnaissance.

• Their bright coloration enhances visibility over long distances and in dense vegetation.
• Ranging rods assist in aligning control points to ensure linear accuracy.
• They can be used as temporary markers during the setup of permanent control points.
• Lightweight construction facilitates easy transport during fieldwork.
• Maintenance involves repainting faded stripes to retain visibility.

2.1.7 Total station

The total station is an electronic/optical instrument combining theodolite and distance measurement functions, critical for control point location with high precision.

• Total stations enable rapid, accurate data collection, integrating horizontal and vertical measurements.
• Their use reduces human errors associated with manual angle and distance readings.
• Data collected can be downloaded for detailed analysis and mapping.
• Regular calibration ensures measurement reliability and accuracy.
• Battery life and environmental protection are important for field performance in remote Kenyan sites.

2.1.8 GNSS receivers

Global Navigation Satellite System receivers provide geospatial coordinates for control points using satellite signals, facilitating efficient and precise positioning.

• GNSS receivers allow surveyors to establish control points without extensive line-of-sight requirements.
• Real-Time Kinematic (RTK) corrections improve positional accuracy to centimetre levels.
• They are essential for integrating survey data with national geodetic frameworks.
• Surveyors must understand satellite geometry and signal interference to optimize data quality.
• Battery management and environmental protection are critical for continuous operation in field conditions.

2.1.9 Sand

Sand is used as a bedding material for control point markers to provide stable, level support and to facilitate drainage around the marker.

Properties of Suitable Sand

Clean, coarse sand with minimal silt content is preferred to prevent water retention that could cause marker displacement. Locally sourced river sand from areas such as Athi River is commonly used.

Application Techniques

During installation, a layer of sand is placed beneath and around the marker before backfilling with soil or concrete. Proper compaction ensures the marker remains firmly seated.

2.1.10 Cement

Cement is used to create concrete foundations for control points, providing durability and resistance against environmental forces.

Cement Types Suitable for Survey Markers

Ordinary Portland Cement (OPC) is the standard choice due to its strength and availability in Kenya. Variants with additives may be used in corrosive or high-moisture environments.

Importance in Control Point Longevity

Concrete bases anchored with cement prevent shifting caused by soil erosion, animal activity, or human interference, especially in urban or high-traffic areas.

Mixing and Application

Proper mixing ratios (typically 1:2:4 cement:sand:aggregate) ensure strength and durability. Surveyors should prepare concrete on-site and pour it around markers promptly to avoid weak bonding.

2.1.11 Iron pin

Iron pins are permanent markers driven into the ground to denote control points, providing a reliable physical reference for survey measurements.

Specifications and Dimensions

Standard iron pins are typically 16mm diameter and 450mm to 600mm long-made of galvanized steel to resist corrosion. Their length ensures adequate embedding depth for stability.

Installation Procedures

Pins are driven vertically into pre-dug holes or directly into soft soil using hammers. The top is often capped or marked for visibility and protection.

Durability and Maintenance

Galvanization protects pins from rust in Kenya’s varying climates. Periodic inspections are necessary to confirm pins remain undisturbed and visible, particularly in areas prone to land development.

Chapter Summary

This chapter covered the essential tools, equipment, and materials required for reconnaissance in topographical surveys, including hammers, pegs, spades, shovels, measuring tapes, ranging rods, total stations, GNSS receivers, sand, cement, and iron pins. It explained how to identify existing control points that serve as reference locations for survey accuracy. The process of selecting suitable topographical survey control points was detailed, emphasizing criteria that ensure reliable and precise measurements. Extending these control points to cover larger survey areas was also discussed, highlighting methods for maintaining continuity and consistency. Finally, the chapter addressed the monumenting of control points, which involves physically marking these locations to preserve their positions for future surveys and reference. Together, these topics provide a comprehensive understanding of establishing and managing control points critical to successful topographical surveying.