Naslov
Hydrologic determination of retardation basines as elements of Zagreb city flood protection system

Autori
Petraš, Josip ; Marušić, Josip

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
IX th World Water Congres, Montreal - Proceedings (Extented Abstracts), Volume I / Shady, Aly M. at al - Montréal : COLLECTION ENVIRONMENT - Universite de Montreal, 1997, 183 - 185

Skup
IWRA (Interantional Water Resources Association)

Mjesto i datum
Montréal, Kanada, 01.09.1997. - 06.09.1997

Vrsta sudjelovanja
Ostalo

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
detention basins; flood protection system; effective runoff; storage volume; discharge hydrograph; composite hydrograph

Sažetak
In 1982 the Water Management Master Plan of Zagreb City (WMMP) was made as the basic document of water management in the wider area of the city. With this document the solution for the protection of Zagreb city against mountain stream floods by building mountain detention basins was accepted. In 1992 a new water management document, Amendments and Additions to the Water Management Master Plan of Zagreb City (AAWMMP), was made. This document took into consideration the guidelines for a systematic approach to the flood protection system. In the WMMP 1982, the methodology for hydrologic computation of high waters in small watersheds of Zagreb streams was defined. That methodology did not take into consideration the fact that the planned detention basins make together with the watercourses integral hydrologic systems. The need for the applying of a systematic approach in carrying out the hydrologic analyses of these detention basins follows from their synergetic effect on the reduction of great water waves. The analyses of the synergetic effect of the detention basins have resulted in the knowledge that the methodology of hydrologic computations presented in the WMMP from 1982 is not suitable for the detetmination of necessary storage volume of the planned detention basins, nor for the deterniination of the regulation dimensions of watercourse channels. Therefore, in the AAWMMP from 1992 a new methodology for hydrologic computations is elaborated and proposed. It is adjusted to the systematic approach to the problem under consideration. The basic characteristics of the methodology given in the WMMP from 1982, and that proposed in the AAWMMP from 1992 are presented in the paper. The WMMP 1982 gave a uniform hydrologic standard for the determination of great water waves from the watersheds of Zagreb streams. This standard contains the regional relation for the computation of maximum discharges in the analytical form Qmax = aFb, and the relation of the type, VRP = f(F;RP) for the determination of the volume of great water waves depending on the return period and watershed area. The mentioned relations mean that for each watershed a rainfall of certain duration and intensity is relevant, i.e. the rainfall resulting in maximum discharge Qmax and maximum water wave volume Vmax for a certain retum period RP. Since the respective watersheds above the detention basins are different in area, it means that by using the relations QRP = aFb and VRP = f(F;RP) while defining the relevant hydrographs for the determination of the storage volume of detention basins and their evacuation facilities, the hydrographs of different rainfall duration would be obtained. Such hydrographs would give unrealistic hydrologic information about the total situation in the watershed, if having in mind the fact that the detention basins act within the system. The hydrographs obtained according to the given relations do not belong to one (and the same) rainfall event, and therefore from the standpoint of the system it can be said that incompatible hydrographs are in question. These hydrographs cannot be thus reliably used for the determination of the storage volume of detention basins or for the determination of dimensions of other elements of the integral flood protection system. Therefore, the conclusion was reached that the hydrologic standards from 1982 should be changed in order to provide the compatibility of hydrographs. The need for their compatibility follows from the fact that all the objects within the same flood protection system work integrally, and thus the effect of a particular structure on the functioning of the system as a whole can be only analysed under condition that the real hydrologic model of the system exists. The fulfilment of the condition that the hydrologic analysis should result with the real hydrologic model of the system of detention basins and watercourse channels in the watershed can be realised by the application of an adequate precipitation-runoff model of particular precipitation. Such models which enable defining of runoff hydrographs on the basis of one real or some estimated precipitation satisfy the condition of the compatibility of hydrographs, because all the hydrographs of particular precipitation are compatible. This particular approach was applied in the hydrologic analysis of Zagreb streams during the elaboration of the AAWMMP 1992. The hydrologic analysis is based on the concept that can be illustrated by the block diagram of defining of real hydrographs.

Izvorni jezik
Engleski

Znanstvena područja
Građevinarstvo

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