Since 1960`s in Poland a phrase "small retention" has been used although it has been unknown in other countries. "Small retention" means various forms of human activity aiming towards limiting the fast water runoff after snow melting and heavy rains. It is believed that water that has been retained in periods of its excess can supply water courses during summer. It can also be used for agricultural purposes as it increases water availability for crops and improves biodiversity of rural areas.Many different methods of water retention have been defined. Among others, increase of potential retention of surface waters can be achieved by construction of reservoirs or damming on rivers and lakes. Ground water retention capacity can be improved by increasing recharge of aquifers and improvement of soil structure in the aeration zone. Due to the form and way of implementation of small retention measures they can be divided into technical and non-technical measures. In other words, small retention can be defined as a set of measures aiming towards reconstruction of natural retention in the catchment that has been modified or destroyed by human activity.In this paper, it has been stressed that activities and tasks undertaken in Europe in recent years under phrase "increase of natural retention" can be covered by the definition of small retention.
The aim of this study was to analyse the impact of selected small water retention measures on surface and groundwater level in river basins. The study was limited to the analysis of measures like small water reservoirs, restoration of bogs and reconstruction of drainage systems in the river valleys. A few study cases were described.
Dutch SIMGRO numerical model describing the regional surface water and groundwater flow has been used for simulation modelling of different cases.
The result of the study has shown that small retention measures are a good and effective method to increase the ability to retain water in the small river basins. Construction of small water reservoirs and weirs on ditches and creeks and restoration of drained bogs can limit the fast outflow of precipitation and melting water from the catchment.
The study has proved that the small water retention measures can be helpful for flood protection and in decreasing of drought threats in small river basins.
Wetlands as one of the most valuable ecosystems are subjects of legal protection. Except ecological value they play important role in water management. Wetlands slow down the outflow of water from river basins and protect the water quality in the agricultural area. Therefore many artificial wetlands are constructed in some countries. The most valuable natural wetlands are protected as National Parks-the highest form of protection. Maintaining high degree of moisture of soil that is a condition that must be fulfilled to preserve the value of these areas can cause conflicts in using the adjacent areas. The paper presents an analysis of conflict situations that occurred in the Biebrza, Narew and Kampinos National Parks. Drainage of the excess water from the built-up area or from the areas used for agricultural purposes interferes with the natural flow regime in the protected areas. The analysis allowed identifying the possible compromise solutions.
According to the Nitrate Directive it is necessary to established a protective belt (ecotones) around lakes. Inside these belts, it is forbidden to use fertilize for agricultural purposes. It is believed that it is the most imported measure to protect water quality in the lake. The analysis were conducted to estimate the sources of nitrogen entering the waters of the lake. Some analysis were conducted to estimate the sources of nitrogen entering waters of the lake. It was proved that the biggest load (more than 80%) of contamination is entering the lake with water flowing in streams and ditches. Only 10% of the chemicals are entering the lake with the groundwater filtrating to the lake. It is very important to use a proper methods of agriculture with proper methods of fertilization in the whole area of river basin flowing to the lakes.
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