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Urbanizacija spremeni lastnosti prispevnega območja in vpliva na posamezne komponente hidrološkega kroga. Povečajo se volumni površinskega odtoka, padavinska voda odteče hitreje, posledično pa se povečajo tudi konice pretokov. Zaradi spremenjenega hidrološkega režima se poruši ustaljeni vzorec hidroloških sprememb in motenj, kar v končni fazi lahko vodi v degradacijo rečnih ekosistemov. Zato so razvili alternativni pristop k upravljanju s padavinskim odtokom, ki temelji na posnemanju osnovnih hidroloških mehanizmov s pomočjo sonaravnih ukrepov, ki površinski odtok zadržijo čim bližje mestu nastanka. V nalogi smo s pomočjo hidrološkega modela preverili, za koliko lahko z različnimi sonaravnimi ukrepi in njihovimi kombinacijami, ki smo jih glede na veljavno zakonodajo, prostorske in tehnične omejitve predvideli na manjšem prispevnem območju v središču mesta Ljubljane, zmanjšamo volumne odtoka in konice pretokov v primeru padavinskih dogodkov z različnimi povratnimi dobami, oziroma v kolikšni meri lahko na ta način omilimo posledice urbanizacije na površinski odtok. Hidrološki model smo umerili s pomočjo podatkov o meritvah padavin in pretokov, ki smo jih izvedli v neposredni bližini obravnavanega območja oziroma na iztoku iz kanalizacijskega sistema. Ugotovili smo, da lahko pri dogodkih s povratno dobo krajšo od enega leta s kombinacijo ponikalnih jaškov, cevnih ponikalnih jarkov in zelenih streh volumne odtoka in konice pretokov zmanjšamo do 45 %, medtem ko je pri dogodku s 100-letno povratno dobo zmanjšanje volumna odtoka le še 12 %, konice pretoka pa 10 %. Ugotovili smo, da so sonaravni ukrepi pri zmanjševanju volumnov odtoka in konic pretokov bolj učinkoviti v primeru manjših dogodkov s krajšo povratno dobo. Urbanization changes characteristics of a drainage area and alters components of a natural hydrologic cycle. Runoff volumes increase, stormwater runs off more quickly and consequently peak flows become larger. Human alteration of the flow regime changes the natural pattern of hydrologic variation and disturbance, which may ultimately lead to river ecosystem degradation. For this reason an alternative stormwater management approach has been devised that mimics natural hydrologic functions by means of sustainable measures which manage rainfall where it falls. This investigation uses a hydrological model to evaluate the effectiveness of different sustainable measures and their combinations in reducing runoff volumes and peak flows on a small drainage area which is representative for a wider city center of Ljubljana. We assumed these measures to be distributed across the drainage area having regard to the current legislation, spatial and technical constraints. The effects were studied for rainfall events of different return periods. Discharge measurements were made at the drainage area outflow and a rain gauge was situated in the vicinity of the study site. In the case of events with a return period of 1 year or less, the runoff volumes and peak flows reduction was approximately 45 % in both cases, when simulating a combination of measures, involving infiltration shafts, pipe infiltration trench elements and green roofs. On the other hand, when simulating the same combination of sustainable measures for a 100 year event, the reduction of runoff volume and peak flow was only 12 % and 10 % respectively. We’ve arrived at a conclusion that sustainable measures are more effective in reducing runoff volumes and peak flows for smaller and more frequent rainfall events. |
