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5. Water-quality decline due to under-performance
When design, installation, or maintenance issues cause under-performance, the system does not remove water as designed and surface runoff increases. As a result, more soil-attached phosphorus moves with surface runoff. A properly functioning drainage system reduces issues from surface runoff, but it increases the transport of nitrate and phosphorus through subsurface drainage discharge. The excess phosphorus in downstream water bodies causes adverse economic, social, and environmental impacts. Also, excess waterlogging conditions resulting from drain clogging or impeded infiltration harms the soil structure and reduces crop yield. The poor soil structure decreases infiltration, causing an increase in surface runoff and nutrient loss.
Generally, improving soil health enhances the performance of drainage systems, but nitrogen and phosphorus losses to surface water are still an issue. Therefore, use conservation drainage practices to reduce nutrient loss while maintaining crop productivity. See Christianson et al. (2016) for more information about conservation drainage practices.
6. Conclusions and recommendations
If there is a drainage system failure, it usually occurs during the first two years after installation. Subsequently, the system should function properly if adequately maintained. Most under-performance problems can be avoided with proper design, installation, and maintenance. However, unforeseen situations can lead to under-performance. Increasing knowledge about design and installation is key to avoiding most under-performance issues. Drainage system users are encouraged to attend educational drainage workshops as a means of increasing knowledge.
The under-performance of a drainage system can lead to yield decline due to slower water removal and lead to poor water quality due to increased surface runoff. The solution for an under-performance issue depends on local conditions. If the under-performance issue is severe, consult a drainage contractor and soil scientist to identify the problem, and address it early to avoid adverse crop and environmental outcomes. Generally, improving soil health improves the performance of drainage systems, but nutrient loss is still an issue. Therefore, use conservation drainage practices to reduce nutrient loss while maintaining crop productivity.