Agricultural surveys form the foundation for effective farm planning and land management. Accurate measurement of land parcels and features is essential for designing irrigation systems, planning crop layouts, constructing farm buildings, and establishing boundaries. In Kenya, agricultural engineers rely on various types of chains for ground measurement, each suited to specific surveying needs and environments. Understanding the characteristics and appropriate applications of these chains ensures precision and efficiency in agricultural projects.

2.1 Types of chains

The selection of a suitable chain for agricultural surveying depends on factors such as measurement accuracy, terrain, and the scale of the survey. Different chains have evolved to meet diverse requirements, ranging from traditional units to metric systems. Kenyan agricultural engineers working in varied contexts, from smallholder farms to large-scale commercial estates, must be familiar with these types to optimize survey results.

2.1.1 Gunter's Chain Survey

Gunter's chain is a historic surveying chain widely used in land measurement, especially in countries influenced by British colonial systems, including Kenya. It measures 66 feet in length and is divided into 100 links, with each link measuring 7.92 inches. This chain was traditionally favored for its ease in calculating acres since 10 square chains equal one acre.

Characteristics of Gunter's Chain

• Length and Division: Exactly 66 feet long, divided into 100 equal links, allowing precise fractional measurements.
• Material Composition: Typically made of steel or brass links connected by rings, providing durability and flexibility.
• Measurement Units: Uses imperial units, which can require conversion to metric for modern Kenyan agricultural projects.
• Suitability: Best for relatively flat terrain where precise area calculation is important.
• Historical Usage: Despite being somewhat outdated, it remains relevant for legal land descriptions and older farm boundaries.

Application in Agricultural Surveys

Gunter's chain is useful in farm parcel surveys where historical land records are in imperial units. For example, a cooperative farm in Nakuru County conducting boundary verification may use this chain to match official land registry descriptions. However, its use requires care with unit conversions to avoid errors in metric-based farm planning.

2.1.2 Metric Chain

The metric chain is a more contemporary tool aligned with Kenya's adoption of the metric system. It is typically 20 meters long, divided into 100 links of 20 centimeters each. This chain facilitates direct readings in meters, simplifying calculations and integration with GPS and other modern surveying instruments.

Features of Metric Chains

• Standard Length: Commonly 20 meters, but variations exist depending on manufacturer and purpose.
• Link Division: Divided into 100 equal links, each 0.2 meters, enabling decimal-based measurements.
• Material and Durability: Constructed from steel or synthetic materials coated for corrosion resistance.
• Ease of Use: Compatible with metric-based mapping and farm planning software used in Kenya.
• Versatility: Suitable for small to medium-scale agricultural surveys requiring moderate accuracy.

Practical Considerations

In a horticultural farm in Thika, metric chains are ideal for laying out irrigation furrows and planting rows due to their compatibility with metric-based design plans. Their length allows efficient measurement without frequent repositioning, reducing survey time.

2.1.3 Engineers Chain

The engineers chain is designed for higher precision and is often 100 feet long, divided into 100 links of one foot each. This chain is commonly used in engineering projects, including farm infrastructure development such as roads, drainage, and buildings.

Distinctive Attributes of Engineers Chains

• Length and Division: 100 feet total length, each link one foot, facilitating direct reading in feet.
• Robust Construction: Made from heavy-duty steel to withstand rough ground conditions.
• Precision Measurement: Suitable for detailed surveys requiring exact distances.
• Application Scope: Widely used in civil engineering projects on farms, including layout of silos and storage facilities.
• Conversion Requirement: Imperial units necessitate conversion to metric for integration with Kenyan agricultural standards.

Usage in Kenyan Agricultural Engineering

At a dairy farm in Meru County, engineers chains assist in accurately positioning cattle sheds and feed storage areas. Their rigidity and length make them suitable for longer distance measurements on relatively even terrain.

2.1.4 Band Chain

Band chains are flexible, tape-like chains made of steel or synthetic materials, often coated to resist rust. They come in lengths ranging from 20 meters to 50 meters and are favored for their portability and ease of handling in dense vegetation or uneven terrain common in Kenyan farms.

Characteristics of Band Chains

• Material and Flexibility: Thin steel bands or synthetic tapes that coil for easy transport.
• Length Variability: Available in various lengths, allowing customization based on survey scale.
• Markings: Metric or imperial graduations printed or engraved for direct reading.
• Suitability for Difficult Terrain: Their flexibility allows measurement around obstacles and through bushy areas.
• Maintenance Needs: Require careful handling to prevent kinks and corrosion.

Application in Agricultural Settings

In a tea plantation in Kericho County, band chains enable surveyors to measure plots through steep and densely vegetated slopes without damaging the chain or the environment. Their lightweight nature reduces fatigue during extended surveys.

2.1.5 Revenue Chains

Revenue chains are specialized chains used by government land surveyors for cadastral surveys related to land ownership and taxation. They conform to standards set by the Ministry of Lands and Physical Planning in Kenya and are often calibrated for legal accuracy.

Defining Features of Revenue Chains

• Standardization: Calibrated and certified to meet legal requirements for land measurement.
• Length and Units: Usually 20 meters long with metric graduations, aligning with Kenya's land registration system.
• Durability: Made from corrosion-resistant materials to maintain accuracy over time.
• Usage Context: Primarily used in land adjudication, boundary demarcation, and official surveys.
• Traceability: Often stamped or marked with serial numbers for official record-keeping.

Role in Kenyan Agricultural Land Management

County government surveyors use revenue chains when adjudicating land parcels for smallholder farmers in Machakos. Accurate measurement ensures fair land allocation and proper taxation, which are critical for sustainable agricultural development.

Chapter Summary

This chapter covered the essential types of chains used in agricultural surveys, including Gunter's, metric, engineers, band, and revenue chains, each serving specific measurement needs. It explored the different chain survey stations, such as main, subsidiary, and tie stations, which are critical for accurate land mapping. The procedures involved in chain surveying were detailed, from reconnaissance and marking stations to chaining, measuring, analyzing, and report writing. Various types of levels were introduced, including dumpy, Abney, wye, tilting, and precision levels, alongside key levelling terms like datum, backsight, foresight, intermediate sight, and height of instrument. The chapter explained different levelling methods such as simple, profile, differential, and reciprocal levelling, highlighting their application in land assessment. Construction materials and their availability for survey work were discussed to emphasize practical considerations. Levelling procedures and booking methods, including height of collimation and rise and fall, were described to ensure accurate data recording. Finally, the chapter examined methods of land grading, its benefits for agricultural productivity, and the limitations that may affect its effectiveness.