This paper presents the concept for the location of two dry water reservoirs designed to retain water led through the main ditch (R) of the drainage system in Łączany. The purpose of the work is to develop a forecast for the reduction in the capacity of planned dry water reservoirs. Planned water reservoirs will allow increasing flood protection of drained areas. Based on geodetic measurements in the selected locations, the capacity of planned dry reservoirs was determined, amounting to 4.08 and 115.49 thousand m3, respectively for the U reservoir formed from the flood relief channel, and the R reservoir, located in the lower course of the R ditch. According to the developed forecast, applying the Gončarov formula, the U reservoir would be 50% silted after 134 years, and the R reservoir would be 50% silted after 149 years. The forecast has been prepared using the method recommended by the guidelines, i.e. it was developed as for reservoirs with constant water damming (accumulation). TE values determined using the Churchill method were adopted in the silting forecast. The estimated forecast indicates a long service life of the reservoirs without the need for their desilting. However, the development of a detailed forecast would require a modification of the calculation methodology, taking into account the determination of the capacity of water reservoirs to retain bed load, typical of dry water reservoirs. In the absence of the method, determination of the service life cycle of water reservoirs can be developed as an estimate.