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Influence of the Hydrogel Amendment on the Water Retention Capacity of Extensive Green Roof Models

Deska Iwona, Mrowiec Maciej, Ociepa Ewa, Lewandowska Agnieszka

Journal of Ecological Engineering

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2020

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Vol. 21, nr 1

195--204

EN

The goal of the research was to investigate the retention capacity of six green roof models (SHP1, SHP2, SHP3, SH, S, and SP) constructed with the use of the square-shaped plastic trays, Floradrain FD 25 drainage elements, SF filter sheets, and the specified extensive substrates (with or without the hydrogel amendment). The SHP1 and SHP2 models were constructed in March 2017, SHP3 and SH – in November 2017, while S and SP – in April 2018. Four models (SHP1, SHP2, SHP3, and SP) contained the plants (the goldmoss stonecrop Sedum Acre), whereas two models (S and SH) did not contain the vegetation. The substrates of SHP1, SHP2, SHP3, and SH models contained the hydrogel admixtures. The investigations were conducted with the use of simulated (and partially natural) precipitations. The water retention capacity of each green roof model was established based on the difference between the precipitation volume and the volume of runoff from a model. The results show that green roofs can be useful stormwater management tools. The calculated stormwater retention rates ranged from 29.50% to 85.15%. In most cases, the best water retention capacity was exhibited by the SHP3 model, constructed in November 2017 and planted in April 2018, containing the substrate amended with superabsorbent (cross-linked potassium polyacrylate). The similarly constructed SHP1 and SHP2 models, which were built in March 2017, in some cases had lower water retention capacity. These models contained older hydrogel and were overgrown with older, smaller, and worse looking plants, partially supplanted by mosses. Such results indicate that the efficiency of hydrogel may decrease over time. In many cases, the S (not vegetated, without hydrogel), SH (not vegetated, with substrate containing hydrogel), and SP (vegetated, without hydrogel) models had slightly lower water retention capacity. The results of investigations indicate that there was a relatively strong positive linear correlation between the retention depth and duration of the antecedent period elapsed from the preceding total (or substantial) saturation of the green roof models (labelled in this article as period since total saturation – PSTS). The weather conditions i.e. air temperature and relative humidity as well as PSTS are very important parameters that influence the retention capacity of the green roof models. The result show that duration of PSTS can be stronger correlated with the retention depth than antecedent dry period (ADP) elapsed from the end of last precipitation, regardless of its depth and intensity.

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Impact of the hydrogel amendment and the dry period duration on the green roof retention capacity

Deska Iwona, Mrowiec Maciej, Ociepa Ewa, Michniewski Michał

Ecological Chemistry and Engineering. S

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2020

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Vol. 27, nr 3

357--371

EN

Abstract: Climate changes as well as the urbanisation and economic development influence the characteristics of the stormwater runoff in the cities. The sealing of drainage basin surface leads to an increase of the runoff intensity, thereby decreasing the rainwater infiltration. This situation can lead to the risk of flooding in urban areas. Therefore, especially in great cities there is a need for application of such solutions that will support the operation of the sewage systems. The examples of such solutions are, among others, the green roofs. The paper presents the results of investigation of the water retention capacity of 4 green roof models containing following growing media: (1) the typical green roof substrate without any amendments, (2) the substrate with addition of about 1 % by weight of hydrogel (the cross-linked potassium polyacrylate), (3) the substrate containing about 0.25 % by weight of hydrogel, (4) the substrate with addition of expanded clay and perlite. The models were not vegetated in order to investigate only the water retention capacity of drainage elements and substrates. The water retention capacity of green roof models was investigated in the laboratory conditions with use of artificial precipitations simulated after diverse antecedent dry weather periods (ADWP) amounting to: 1, 2, 5, 7, and 12 days. The intensities of artificial precipitations were relatively high and ranged from 1.14 to 1.27 mm/min, whereas their durations ranged from 7.75 to 12.56 min. These values of intensities and durations corresponded to the design rainfall intensities calculated using Blaszczyk’s equation for annual rain depth equal to 600 mm and the return periods ranged from 5 to 15 years. The obtained results indicate that the water retention capacity of green roof models, expressed as the volumes (or depths) of rainwater retained within their structures, increases with an increase of ADWP. Results indicate that the relation between ADWP and the amount of water retained in the layers of green roofs in the case of relatively short antecedent dry weather periods provided for the analysis (from 1 to 7 days) may be approximately linear. The results of the one-way ANOVA indicate that in the case of all models there is a statistically significant difference between the values of retention depth for specified ADWP (p < 0.001). During more than half of simulated precipitations, especially in the case of longer ADWPs lasting 5, 7, and 12 days the best water retention capacity had Model 3, with substrate containing about 0.25 % by weight of hydrogel. On the other hand, the results show that the weakest retention capacity had Model 2 (with substrate containing 1 % by weight of hydrogel). In the case of longer ADWPs (lasting 7 and 12 days) relatively weak water retention capacity had Model 4 (with substrate containing the addition of expanded clay and perlite). It can be concluded that too large amount of hydrogel added to the substrate can have an unfavourable impact on the water retention capacity of green roofs.

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Wpływ warstwy roślinności oraz dodatku hydrożelu do substratu na zdolności retencyjne zielonych dachów

Deska Iwona, Mrowiec Maciej, Ociepa Ewa, Ślęzak Katarzyna

Proceedings of ECOpole

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2019

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Vol. 13, No. 1-2

107--118

PL

Na terenach zlewni zurbanizowanych, obok tradycyjnych systemów kanalizacyjnych, coraz częściej stosuje się zrównoważone systemy drenażu (ZSD, ang. SUDS - Sustainable Urban Drainage Systems), które umożliwiają zagospodarowanie wód opadowych możliwie jak najbliżej miejsca wystąpienia opadu. Jednym z przykładów takich rozwiązań są zielone dachy. W artykule zaprezentowano wyniki badań zdolności retencyjnych sześciu modeli zielonych dachów, oznaczonych w tekście artykułu symbolami: SHR1, SHR2, SHR3, SH, S i SR. W przypadku modeli SHR1, SHR2, SHR3 i SH zastosowano dwie warstwy substratu ekstensywnego o nazwie handlowej „Skalny kobierzec”. Dolna warstwa substratu zawierała domieszkę 0,5 % wag. hydrożelu potasowego (usieciowanego poliakrylanu potasu), natomiast górną warstwę stanowił ww. substrat bez domieszek. W przypadku modeli SHR1, SHR2, SHR3 zastosowano warstwę roślinności - rozchodnik ostry (Sedum Acre), natomiast model SH nie zawierał warstwy roślinności. Z kolei w przypadku modeli S i SR zastosowano jednolitą warstwę substratu ekstensywnego „Skalny kobierzec” bez dodatku hydrożelu, przy czym model SR posiadał warstwę roślinności (rozchodnik ostry), a model S był pozbawiony roślin. Modele SHR1 i SHR2 zostały skonstruowane w marcu 2017 r., modele SH i SHR3 w listopadzie 2017 r., a modele S i SR w kwietniu 2018 r. Badania były prowadzone z zastosowaniem opadów naturalnych oraz sztucznych (symulowanych). Na podstawie otrzymanych wyników można stwierdzić, że zastosowanie zielonych dachów może pozwolić na zmniejszenie natężenia odpływu wody opadowej ze zlewni. Uzyskane wyniki wskazują, że w większości przypadków najlepsze zdolności retencyjne wykazywały modele zielonych dachów obsadzone dobrze ukorzenioną, gęstą warstwą roślinności, które równocześnie zawierały substrat z domieszką hydrożelu (SHR1, SHR2). W niewielkim stopniu niższą zdolnością retencyjną charakteryzował się model o bardzo zbliżonej konstrukcji (SHR3), posiadający rzadszą i słabiej ukorzenioną warstwę roślinności. W większości przypadków mniejsze objętości wody były retencjonowane w warstwach pozostałych modeli: S (niezawierającego roślin ani domieszki hydrożelu), SR (zawierającego roślinność, ale niezawierającego hydrożelu) i SH (zawierającego domieszkę hydrożelu, lecz nieposiadającego warstwy roślinności). Otrzymane wyniki wskazują, że dodatek hydrożelu może wpływać pozytywnie na zdolności retencyjne dachów obsadzonych roślinnością, pod warunkiem, że okres bezdeszczowy poprzedzający opad nie będzie bardzo krótki i dach częściowo odzyska zdolność do retencjonowania wody. Na podstawie uzyskanych wyników można stwierdzić, że dodatek hydrożelu do substratu w przypadku modelu pozbawionego roślinności nie powodował znaczącego zwiększenia jego zdolności retencyjnych. Otrzymane wyniki wskazują, że dużą rolę w retencjonowaniu wody opadowej odgrywa warstwa roślinności, zwłaszcza w okresie późnej wiosny i lata, kiedy panują stosunkowo wysokie temperatury.

EN

In urbanized areas, in addition to the traditional sewer systems, increasingly are used the sustainable urban drainage systems (SUDS), inter alia, the green roofs. The focus of the research described in the article was to investigate the retention capacities of six green roof models denoted in the paper by symbols: SHR1, SHR2, SHR3, SH, S, and SR. The models were constructed with use of the plastic garden trays (with internal dimensions 55.7 × 55.7 × 7 cm). On the bottom of each tray the drainage element Floradrain FD 25 was placed. On each drainage element the filter sheet SF (70 × 70 cm) was spread. On the surface of each filter sheet the required amount of the specified substrate was placed. The total thickness of substrate layer on each model was equal. Models SHR1, SHR2, SHR3, SH were built of two layers of the extensive substrate “Sedum Carpet”. The lower layer contained the admixture of 0.5 % by weight of hydrogel (the cross-linked potassium polyacrylate). The upper layer consisted of the substrate “Sedum Carpet” without hydrogel amendment. Models SHR1, SHR2, and SHR3 contained the layer of vegetation - the goldmoss stonecrop (Sedum Acre), while model SH did not contain the plants. The models S and SR contained the uniform layer of extensive substrate “Sedum Carpet” without hydrogel amendment. The model SR contained the vegetation (the goldmoss stonecrop) and S did not contain plants. Models SHR1 and SHR2 were constructed in March 2017, models SH and SHR3 were constructed in November 2017, and models S and SR were constructed in April 2018. The investigations were conducted with use of natural and artificial (simulated) precipitations. The obtained results show that the green roofs can help to reduce the outflow of rainwater from the catchment. The results indicate that in most cases the best retention capacities had models prepared in March 2017, with dense, well-rooted plants and substrate layer amended with hydrogel (SHR1 and SHR2). The similarly constructed model (SHR3) having a less dense and less rooted vegetation layer had a slightly lower retention capacity. In most cases smaller volumes of water were stored in the layers of other models: S (substrate without hydrogel amendment and without plants), SR (substrate without hydrogel amendment + plants), and SH (substrate with hydrogel amendment and without plants). The obtained results indicate that the addition of hydrogel into the growing medium can have a positive effect on the retention capacity of vegetated roof, provided that the antecedent dry period will not be very short. On the other hand, the results show that the hydrogel amendment did not cause a significant increase in retention capacity in the case of model without plants. The obtained results indicate that the vegetation layer plays an important role in the retention of rainwater, especially in the late spring and summer, when the temperatures were relatively high.

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Zrównoważone zarządzanie wodą w miastach w warunkach zmian klimatycznych

Mrowiec Maciej, Ociepa Ewa, Malmur Robert, Deska Iwona

Problemy Ekorozwoju

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2018

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Vol. 13, nr 1

133--138

EN

Increasing global change pressures like urbanisation, climate change, deterioration of urban water infrastructure, cities have difficulties in efficiently managing water resources. To manage these challenges cities have to improve the efficiency of urban water systems by rethinking old paradigms and developing more sustainable solutions.. Between 1.8 and 2.5 % of the annual global GDP is needed for implementation of water-related sustainable development goals. Currently the main challenge is to ensure public health and satisfy water needs while protecting the quality and quantity of water resources for future generations by efficient production and use of water, energy and materials. The paper presents principles to develop water-sensitive cities that ensure access to safe water and sanitation and also to increase resiliency to floods and droughts.

PL

Zarządzanie zasobami wodnymi w obszarach miejskich jest coraz bardziej problematyczne z uwagi na intensywną urbanizację, zmiany klimatu oraz starzenie się miejskiej infrastruktury wodnej. Aby sprostać tym wyzwaniom, miasta muszą poprawić efektywność miejskich systemów wodnych poprzez odejście od dotychczasowych paradygmatów i opracowanie bardziej zrównoważonych rozwiązań. Obecnie około 1,8 ÷ 2,5% rocznego światowego PKB potrzebne jest do realizacji celów w zakresie zrównoważonego rozwoju gospodarki wodnej. Głównym wyzwaniem jest zapewnienie zdrowia publicznego i zaspokojenie potrzeb w zakresie dystrybucji wody, przy jednoczesnej ochronie jakości i ilości zasobów wodnych dla przyszłych pokoleń dzięki wydajnej produkcji i wykorzystaniu wody, energii i surowców. W artykule przedstawiono główne wytyczne dla rozwoju miast zapewniających bezpieczne źródła i systemy dystrybucji wody, odprowadzenie i oczyszczenie ścieków, a także zwiększenie odporności miast na występowanie zjawisk powodziowych oraz okresów suszy.