Excavated Pits and Ponds: Effective Water Storage

In rain-fed agricultural regions, the difference between a productive season and a failed harvest often comes down to one factor: stored water. When rainfall is erratic and perennial streams run dry, farmers need dependable on-farm water reserves. Excavated pits and ponds – among the oldest water storage methods known to agriculture – answer this need directly. By digging into the earth to capture surface runoff from rainfall and seasonal streams, these structures give farmers, livestock keepers, and fish farmers a buffer against water scarcity that no amount of good soil or seed can replace.

What are excavated pits and ponds? 🔗

Excavated pits and ponds are man-made water storage structures created by digging into the ground to form a basin that collects and retains water. Humans have long been excavating basins to retain water for agricultural purposes, and these structures remain globally widespread as a core component of on-farm water management. Their primary function is to capture surface runoff – water flowing over the land surface after rainfall – and store it for later use in irrigation, livestock watering, and aquaculture. Unlike large dams or reservoirs, excavated pits and ponds are modest in scale, making them practical for individual farms and smallholdings.

The design, depth, and layout of an excavated pond are dictated largely by the local terrain, soil type, and rainfall pattern. The two main types of pond structures are excavated (dugout) ponds and embankment ponds, with hybrid forms suited to specific topographies. Understanding each type is essential to selecting the right structure for a given site.

Types of excavated pits and ponds 🔗

Dugout ponds 🔗

Dugout ponds are the simplest form of excavated water storage. A basin for holding water is created by excavating soils in an area which is generally flat or in a depression or low point within a broad drainage way. These ponds do not require embankments, as the surrounding ground level contains the stored water within the excavated depression. They are particularly effective where the water table is relatively shallow, since groundwater seepage can supplement rainfall-fed inflow and help maintain water levels during dry periods.

Dugout farm ponds are found suitable where topography does not permit the construction of an embankment. In flat terrain where constructing a dam or bund would be impractical, dugouts provide the most workable solution. The soil type is critical here – sites with average to high clay content are ideal because they provide a tight base that reduces water loss, whereas sandy soils allow excessive seepage and may require artificial lining to retain water effectively.

Embankment ponds 🔗

Embankment ponds are constructed on sloping or hilly terrain by building an earthen dam or bund across a natural depression, valley, or drainage path. The embankment acts as a barrier that intercepts runoff flowing downslope and holds it back to form a reservoir. These structures are placed on sloping lands to accommodate incorporation of the embankment with natural ground on the upslope side of the pond, and the soil used for the embankment is often sourced directly from within the pond basin during excavation – a practical arrangement that reduces material costs.

The embankment must be properly compacted and protected against erosion. A hardy cover of grasses on the embankment slopes provides erosion resistance. A critical design component is the spillway – a controlled overflow structure that safely discharges excess water during heavy storms. The main function of the emergency spillway is to protect the embankment from overtopping due to an unexpected increase of inflow, which could otherwise cause catastrophic dam failure.

Dugout-cum-embankment ponds 🔗

Dugout-cum-embankment ponds combine both approaches and are best suited to undulating or gently rolling terrain where neither a pure dugout nor a full embankment pond is optimal. Surface ponds of this type are partially excavated where an embankment is constructed to retain water, and are generally constructed at sites where a land depression already exists, allowing the excavated soil to build up the embankment while the dug basin contributes to overall storage volume. This dual approach maximises storage capacity at a lower cost per unit volume compared to building each component separately.

Site selection and soil considerations 🔗

The success of any excavated pond hinges on choosing the right site. Soil permeability is the first factor to assess. Ponds fed by surface runoff must have impermeable soils beneath the pond basin to prevent excess downward seepage, otherwise the pond will not maintain water. Soils with a sufficient proportion of silt or clay are best, and test pits dug at the proposed site before construction allow a proper assessment of soil suitability.

The catchment area – the land surface from which runoff drains into the pond – must be large enough to fill the pond at least once annually. Ponds that depend on surface runoff as their main water supply must be sized such that there are at least two to three acres of drainage area for every acre-foot of pond storage. Too large a catchment, however, can also pose problems – excessive inflow during storms risks damaging embankments and spillways, so the catchment-to-storage ratio must be carefully balanced.

Beyond soil and catchment, the site should be free of contamination from farm waste, livestock corrals, or sewage lines that could degrade water quality. Accessibility for maintenance equipment is another practical consideration that is often overlooked during initial planning.

Key design components 🔗

A well-designed excavated pond is more than just a hole in the ground. Several structural components determine how effectively – and how safely – it operates.

Depth is one of the most important design variables. Deeper ponds store more water per unit of surface area, which reduces both evaporation losses and seepage losses relative to the volume stored. Just by increasing depth by one meter, one can significantly reduce evaporation loss because surface area is reduced, and seepage loss because the wetted area is reduced – and the cost of lining can also be minimised.

Inlet and outlet structures control the flow of water into and out of the pond. The inlet should be designed to channel runoff into the pond without causing erosion at the point of entry – stone pitching or energy dissipators are commonly used. The outlet allows controlled release of stored water for irrigation or livestock use, and must include mechanisms to prevent the pond from draining unintentionally.

Lining may be necessary in soils with high sand content. Clay, compacted soil, and synthetic geomembranes such as HDPE (high-density polyethylene) are common lining options. An impermeable synthetic liner on the bed of the pond can prevent seepage, while strategically placed vegetation along the banks can reduce wind-driven evaporation and prevent bank erosion.

Uses of excavated ponds in agriculture 🔗

Irrigation 🔗

Stored runoff from excavated ponds is one of the most reliable on-farm irrigation sources in rainfed farming systems. A farm pond is a dug-out pond constructed in or near the farm, where rainwater is collected and stored for future uses such as irrigating crops, recharging groundwater, aquaculture, and providing drinking water for farm animals. Research from the Sundarban delta in West Bengal found that converting just 20% of a farm or watershed area into on-farm reservoirs can harvest sufficient excess rainwater to meaningfully supplement crop irrigation. In practical terms, a pond measuring 40 m × 40 m is sufficient to provide irrigation to 1 hectare of land, demonstrating that even modest-sized ponds can have a significant agronomic impact.

Livestock watering 🔗

Ponds provide a consistent water source for cattle, sheep, goats, and other farm animals, particularly during the dry season when natural streams and surface water sources run low. A uniform distribution of ponds minimises overgrazing in the areas around a particular water site, making pond placement an important factor in pasture management. Fencing around the pond perimeter is often recommended to prevent direct livestock access to the water body, which can cause bank erosion and degrade water quality.

Fisheries and aquaculture 🔗

Excavated ponds are widely used for freshwater fish culture, making them a source of both nutrition and income for farm households. A pond that is constructed and managed properly may yield from 100 to 300 pounds of fish annually for each acre of water surface. Water quality management is central to productive fish farming – maintaining adequate dissolved oxygen, appropriate pH levels, and controlled turbidity are all essential. Maintaining an optimal level of dissolved oxygen is essential for fish production, with a recommended concentration of 5 mg/l.

Managing water losses: evaporation and seepage 🔗

Two factors continuously reduce the volume of water stored in an excavated pond: evaporation from the water surface and seepage through the pond walls and floor. Both must be accounted for in design and ongoing management. Water losses by seepage vary depending upon soil conditions at the pond and local water table conditions and may range from 1 to 4 feet per year, and evaporative losses can be substantial in hot, windy conditions. Seepage rates tend to decline as ponds age and organic matter accumulates in their bottoms to seal off pore space in the soil – a natural self-sealing process that improves over time in well-managed ponds.

Practical measures to reduce water losses include lining with clay or geomembranes, planting windbreaks around the pond perimeter, and optimising pond depth to minimise the surface-area-to-volume ratio. Regular inspection of embankments and spillways after heavy rainfall events is equally important to catch any structural damage before it worsens.

Advantages of excavated pits and ponds 🔗

Excavated ponds offer several practical advantages over other water storage options. They are relatively low-cost to construct, especially when local labour and machinery are used and the excavated soil is repurposed for embankment construction. They require no complex plumbing or electrical systems, keeping operational costs low. Rainwater containment ponds are among the most inexpensive ways to collect and preserve rainwater for future use, and their multipurpose nature – serving irrigation, livestock, fish farming, and groundwater recharge simultaneously – enhances their value considerably. Unlike rooftop or tank-based systems, ponds can be scaled to the specific needs of a farm and positioned wherever the catchment geography is most favourable.

Where soil moisture data and rainfall records are available, farmers can also use pond storage to buffer crop production against short dry spells within a season, reducing the vulnerability that comes with complete dependence on rainfall timing. Water harvesting – the capture and storage of rainwater for use during dry periods – is a technology proven to increase food security in drought-prone areas, and excavated ponds remain one of its most accessible and enduring forms.

What do you think? If you were selecting a site for an excavated pond on a farm with mixed flat and hilly terrain, which type of pond – dugout, embankment, or dugout-cum-embankment – would be most practical, and what soil or rainfall factors would drive that decision? Beyond irrigation, how might a single well-designed farm pond simultaneously serve multiple agricultural needs throughout the year?

References

1. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/farm-ponds
2. https://www.fairfaxcounty.gov/soil-water-conservation/building-farm-or-amenity-pond
3. https://dec.ny.gov/regulatory/permits-licenses/waterways-coastlines-wetlands/protection-of-waters-program/constructing-recreational-and-farm-ponds
4. https://www.geographynotes.com/farm-ponds/how-to-design-and-construct-farm-ponds-geography/6152
5. https://fw.ky.gov/Fish/Pages/Farm-Pond-Management-Planning-and-Construction.aspx
6. http://ecoursesonline.iasri.res.in/mod/page/view.php?id=2196
7. https://westernliner.com/blog/how-to-keep-farm-pond-full-of-water/
8. https://directives.nrcs.usda.gov/sites/default/files2/1712930891/31804.pdf
9. https://www.bivatec.com/blog/water-quality-and-bottom-soil-management-of-fish-ponds
10. https://edis.ifas.ufl.edu/publication/AE143
11. https://www.globalseafood.org/advocate/assessing-reducing-pond-seepage/
12. https://www.btlliners.com/types-of-rainwater-harvesting-systems
13. https://en.wikipedia.org/wiki/Rainwater_harvesting