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- Unintentional negative impacts on water downstream when not carefully designed. Especially when the floodwater never reaches the sea – in this case, all water is already allocated in the basin and withdrawal in one place will be more likely to negatively affect another.
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==Resilience to changes in the environment==
====Drought====
'''Effects of drought''': Lower crop yields.
'''Underlying causes of effects''': Less water to crops from flooding.
'''To increase resiliency of WASH system''': Drought-resistant & fast-growing crops; Diversify livelihoods of farmers.
====Floods====
Spreading basins are perfect for areas with floods. They are built to transfer excess water away from rivers, so that uncontrollable floods don't happen in unwanted places. However, in the event of too much flooding, the spreading basin must be large enough to handle the increased volumes of rain. Plus, with intense rain events, the higher velocities might be too much for the soil of the basin and create a washed out effect or likely just runoff before infiltrating. In this case, additional vegetation enhancement (to help the soils absorb more water), wetland enhancement, levee protection, and/or additional water storage will be helpful.
==Construction, operations, and maintenance==
'''General advice on cement''': A common cause of cracks in structures and linings (e.g. in tanks, dams, waterways, wells) is errors in mixing and applying the cement. First of all, it is important that only pure ingredients are used: clean water, clean sand, clean rocks. The materials have to be mixed very thoroughly. Secondly, the amount of water during mixing needs to minimal: the concrete or cement needs to be just workable, on the dry side even, and not fluid. Thirdly, it is essential that during curing the cement or concrete is kept moist at all times, for at least a week. Structures should be covered with plastic, large leaves or other materials during the curing period, and kept wet regularly.
'''Specific advice''':
* It is better to concentrate efforts on low-cost diversion structures and to avoid sophisticated technological solutions. Efforts should be based on improving existing intakes.
* If using controlled flooding for irrigation, farmers should be more involved in development of improved spate systems – the new system should build on existing practices and land rights, not undermine them as has happened in the past.
