Hidrológiai Közlöny 1964 (44. évfolyam)

9. szám - Somogyi Miklós–Lenkey Tibor: Az 1963. szeptemberi gyömrői rendkívüli felhőszakadás

Somogyi M.—Lenkey T.: A gyömrői felhőszakadás Hidrológiai Közlöny 1964. 9. sz. 405 uejiHMHHbi TbicniH jieT. 143 BbinafleHHoro ocaAKa c BejiniHOÍ! 1,5 KM

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(

). Erosion was promoted by the plow-floor which can be still found in many places. Soil erosion of varying extent was experienced on more than 4000 heotares around the centre. b) Damagesi n valleys. Structures in the valleys suffered almost without exception damages. Tail aprons and side slopes of weirs were scoured and destroyed. From the bed-load retent ion structures one burst and a second was damaged by overtopping (Figs. H and 9). The flood waves on the Lower Tápió and Sápi Creek destroyed two reinforced concrete bridges while the water pouring down in the Rákos Creek burst the dams of the Gödöllő fish ponds. 3. Hydrology. Data available for determining the magnitude of the passing flood waves were very scarce. The flood oceurred during the niglit hours so t hat current metering proved impossible. Undisturbed measuring sections would have been difficult to find since the flow oceupied tho ontire width of the valley floor and inundated roads and buildings. On the basis of several site inspections and cross section surVej s the flood discharges were estimated by tho weir formula (at roads), the formula for flow under pressure (at bridges), or by using Chezy's formula at undisturbed valley sections. Comparing the results with the flood discharges of different probability of occurrencc determinod by the Planning Institute for Civil Engineering Structures it was found that tho probability of occurronco of the passing flood wave attained in somo places thousand years (Fig. 6). An attempt has been made to compile the flood hydrograph in Fig. 5. Travelling times were estimated according t o Salcher- Ilosenauer. • 4. Experiences and conclusions. The rainfall in question was of an extraordinary magnitude and no modifications to existing structures must be contemplated where tliose were dimensioned in accordance with valid specifications on probability of occurronco. Increased soil protection is necessary. Plow-floors must be eliminated and steep eroded valley sides must be afforested. Bed-load retention structures must be observed carefully to detect damages in time. Present practice of dimensioning tailwater aprons must be revised. llydraulic structures must be designod to resist without destruction flood waves exceeding the design value. The hydrological and hydrometoorological network must be developed further, especially further ombrographs should bo installed.