A forest is the form of natural storage reservoir and it by this can be perceived as mainstay of small water retention. The prognoses of unfavourable climatic changes (growth of air temperatures, diminishing of precipitations, frequency increase of extreme weather phenomena) causing a necessity of compensations these the unfavourable phenomena by a technical and un-technical undertakings to increase water storage in forests. The building of devices of small retention has reason both: natural (i.a. assure in forest ecosystems biodiversity) and economic aspects. Indicatory cost water storage 1 m3 of water in objects of small retention is ten times smaller than in great storage reservoirs. Permission to building of objects of small retention is required for damming height 1,0 m or for every investment situated on protected areas. More than once its very increased the costs of investment. Therefore building a small objects is pragmatic, e.g. a cascade systems reservoirs. The building of objects damming and slowing outflow from catchments is focused to protection of the valuable natural habitats and it can be use full in strategy of protection of areas - may be the essential element Nature 2000 (e.g. forest bogs ecosystems, moist or flood plain forest). In Poland at ...
