Structural Protection
When your pond relies on a compacted soil/clay layer to prevent stored water from seeping away, it’s important to take additional precautions that aren’t necessary with a geotextile liner. Specifically, layers of soil and clay become less stable as they dry out, which can happen at first fill, after an extended dry period, or when the level of the pond has been rapidly drawn down. When this happens, soil and clay particles shrink and do not form a gapless seal. Rapid filling in this circumstance can cause piping failure.
Ideally, a farmer will be able to keep pond embankments constantly moist. In that case, the soil and clay will remain expanded and minimize the likelihood of cracks appearing.
It’s not always possible to avoid drawing down your irrigation reservoir during dry periods - after all, that’s why you installed one in the first place! To prevent the problem of losing your clay and soil seal, potentially several times per year, consider using a geosynthetic liner. Reinforced woven polyethylene liners are impermeable and aren’t dependent on the presence of water. They are thin, lightweight, and remarkably fast and easy to install compared to other liner options. If your pond is likely to remain empty or low for extended periods of time, consider a liner coated with extra UV protection to prevent UV degradation.
With an embankment dam, it’s critical to keep the water level at or below the freeboard limit. If you’re at the freeboard and a large storm is in the forecast, it’s wise to release some water through the spillway so there is enough room to accept a potential deluge. A reservoir that over-fills to the point that water is flowing over the top of the dam can cause significant damage to the structure of the dam and potentially lead to dam collapse, with the chance of causing property damage and even loss of life downstream.
Inspections
Watershed: While most irrigation pond owners will focus on the pond itself, it’s important to be aware of changing conditions within the pond’s watershed, or the (typically) upslope land which drains into your pond. Changes in the watershed can affect both the quality of your water and the structural health of the pond itself.
Keep an eye out for new areas of land disturbance, whether that involves construction, clearing trees, or even fires. Any of these situations can lead to extensive erosion which will impact your system’s ability to divert and collect water, as well as quickly reduce the overall storage capacity of your pond. Any new activity which increases the likelihood of contamination of the runoff should be carefully considered as well. New pastures or even animal waste lagoons can contribute high levels of nutrients and pathogens to the runoff water, and you’ll need to ensure your pond is prepared to handle the onslaught.
Ponds and Embankments
Erosion is the big bugaboo for ponds and reservoirs, especially embankments. During regular inspections (twice a year at minimum, plus after heavy rains), check carefully along the banks and both upstream and downstream faces of an embankment for signs of erosion. These include excessively soft areas, cracks, settlement, or seepage, and slumps or bulging. If any signs are present, take photographs and measurements, and return soon to monitor changes. If signs are worsening rapidly, consult a qualified engineer quickly to avoid potentially irreparable damage to the embankment.
For excavated ponds, look for changes in the bank shape, undercuts, collapses, or signs of intrusion from outside sources. Mud bubbling up from the floor could indicate that the water table has connected with your pond, for example, which could be a real problem if that’s restricted by state or local laws. If you’re using a geosynthetic liner, you’re unlikely to see these signs of intrusion, but large bubbles (blisters) forming beneath the liner could indicate similar problems.
Pond and Drainage Structures
Check inlets and outlets to ensure they’re not blocked, and any control mechanisms are operating properly. Look at the ditches, swales, or berms that direct water towards your pond and make sure they’re not causing erosion or being frequently overwhelmed by stormwater. Look for muddy water or excess turbidity beyond the intake point, or during periods when there’s not been a recent storm. For embankment ponds, verify that the water level doesn’t exceed the designated freeboard. Monitor changes in water level - rapid changes not attributable to storms or purposeful drawdowns should be identified and addressed.
Maintenance
Once an irrigation pond or reservoir has been established, the primary risk factors to its operation and longevity are insufficient monitoring and deferred or incomplete maintenance. Storage ponds should be maintained at a “new” level as long as they’re in operation. Even minor deterioration can quickly worsen and lead to complete failure.
Embankments and shores of excavated ponds should be covered with well rooted perennial grasses. If necessary, plan to re-seed and fertilize embankments as needed to maintain a dense, healthy vegetation cover. Keep the area mowed, both to improve your ability to inspect the embankment, and to prevent the emergence of trees and shrubs, whose deep roots can disturb its foundations. Burrowing animals also present major risks, so any signs should be quickly addressed. If fencing is used to protect ground cover on the embankment or on the borders of the storage area, inspect the fencing and keep it in good condition. If access by livestock or wildlife is inevitable, establish some gravel approaches and ramps that allow animals to drink without trampling the edges.
Always keep both inlets and outlets, ditches and swales free of debris and trash. If aquatic weeds or algae are clogging pump intakes or causing safety and aesthetic concerns, look at our next article about managing algae and other water storage challenges.
