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Remote sensing and multi criterion analysis for identifying suitable rainwater harvesting areas

Debebe Yalembrhan, Otterpohl Ralf, Islam Zubairul

Acta Geophysica

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2023

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Vol. 71, no. 2

855--872

EN

Water scarcity and soil erosion are the main constraints small holder farmers are facing in Tigray, the northern most part of Ethiopia. Both very high and very low precipitation can cause a damage to agriculture which is the case in semi-arid regions like Tigray. While too little rainfall cannot support the growth of crops resulting in crop failure, the short but intense rainfall also causes a runoff thereby washing away essential soil nutrients. Installation of different micro/macro-catchment rainwater harvesting can address both water scarcity and soil erosion if they are properly designed prior to construction. This research was intended to develop a methodology for identifying suitable rainwater harvesting (rwh) sites by using weighted overlay analysis. It also utilizes Ahp (analytical hierarchy process) as effective multi-criterion decision-making tool in eastern Tigray at Kilte Awlaelo district on an area of 1001 km2 . This method was chosen because it is simple to use, cost effective, flexible and widely adopted. Physical, hydrological, climate and socio-economic aspects were taken into account during criteria selection. The result indicated four suitability classes with 8.74% highly suitable areas (85.25 km2 ), 56% suitable areas (550.75 km2 ), 30.8% moderately suitable areas (303.2 km2 ) and 4.46% less suitable areas (43.87 km2 ). The produced rwh suitability map was also validated by both ground truth on google earth pro and a field trip to the study site. In situ and ex situ rwh including bench terraces, wells, and enclosure areas were identified during the field visit that verified the suitability model. Finally, depending on weight and scale of criteria and sub-criteria that matched to each identified suitable areas, different micro-catchment and macro-catchment techniques of water harvesting are recommended. This methodology can be utilized as decision-making tool for rwh practitioners, local and foreign organizations working on soil water conservation programmes and policy-makers during their early planning stages.

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Converting sewage holding tanks to rainwater harvesting tanks in Poland

Murat-Błażejewska Sadżide, Błażejewski Ryszard

Archives of Environmental Protection

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2020

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Vol. 46, no. 4

121--131

EN

The aim of this study was an assessment of feasibility of conversion of sewage holding (SH) tanks to rainwater harvesting (RWH) tanks in Poland. Such a conversion may partly solve the problem of water scarcity for irrigation of plants in individual small gardens and reduce tap water consumption. Seven methods of RWH tanks sizing were applied to an example of a small harvesting system of the roof area equal to the garden irrigation area of 100 m2 for three different irrigation doses. A new criterion was introduced to optimize the tank capacity. Economic optimization was provided for new RWH tanks and for the tanks adapted from abandoned SH tanks. Results obtained for a system sited in west-central Poland in an average year have shown that design capacity of RWH tanks varied markedly between sizing methods. The conversion of SH tanks to RWH tanks is profitable, especially for irrigation due to scarcity of water in relatively dry west-central regions. Conversion of individual SH tanks in a good technical state to RWH tanks is relatively simple and cheap. The potential increase in storage volume due to the conversion of individual SH tanks to RWH tanks could reach all over Poland 215–350 dam3 per year, and individually can save up to 18–25% of total annual water use.

PL

Celem pracy była ocena możliwości przekształcenia zbiorników bezodpływowych do ścieków (ZB) w zbiorniki do gromadzenia wody deszczowej (WD) w Polsce. Taka konwersja może częściowo rozwiązać problem niedoboru wody do nawadniania roślin w małych ogrodach przydomowych i zmniejszyć zużycie wody wodociągowej. Zastosowano 7 metod określania wielkości zbiornika WD na przykładzie małego systemu zbierającego opady z dachu o powierzchni równej powierzchni nawadnianego ogrodu (100 m2) oraz do alimentacji domowej instalacji wodociągowej w ilości 140 dm3/d. Wprowadzono nowe kryterium optymalizacji pojemności zbiornika, bazujące na efektywności hydraulicznej. Optymalizację ekonomiczną wykonano dla nowych zbiorników WD oraz dla zaadaptowanych z wyłączonych z eksploatacji ZB. Wyniki uzyskane dla systemu zlokalizowanego w środkowozachodniej Polsce i symulacji wykazały, że pojemność projektowa zbiorników WD różniła się znacznie między metodami wymiarowania. Konwersja ZB na zbiorniki WD jest opłacalna, szczególnie w przypadku nawadniania roślin w okresach niedoboru wody, a konwersja do instalacji wspomagającej wodociąg sieciowy jest jeszcze bardziej opłacalna, gdyż okres jej zwrotu wynosi od 2 do 6 lat. Przekształcanie indywidualnych ZB w zbiorniki WD i POŚ jest stosunkowo proste i tanie. Potencjalny wzrost pojemności retencyjnej w wyniku konwersji indywidualnych ZB na zbiorniki WD może osiągnąć w całej Polsce 215–350 tys. m3 rocznie, a indywidualnie może zaoszczędzić do 40% całkowitego rocznego zużycia wody.

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RS and GIS based modeling for optimum site selection in rain water harvesting system: an SCS CN approach

Mahmood Khalid, Qaiser Ansab, Farooq Sumar, Nisa Mehr un

Acta Geophysica

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2020

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Vol. 68, no. 4

1175--1185

EN

In this study, an integrated approach has been adopted for optimum selection of locations for rain water harvesting (RWH) in Kohat district of Pakistan. Various thematic layers including runof depth, land cover/land use, slope and drainage density have been incorporated as input to the analysis. Other biophysical criteria such as geological setup, soil texture and drainage streams characteristics were also taken into account. Drainage density and slope were derived from digital elevation model, and map of land use/land cover was prepared using supervised classifcation of multi-spectral Sentinel-2 images of the area. Aforementioned thematic layers are assigned respective weights of their importance and combined in GIS environment to form a RWH potential map of the region. The generated suitability map is classifed into three potential zones: high, moderate and low suitability zones consisting of area 638 km2 (21%), 1859 km2 (62%) and 519 km2 (17%), respectively. The suitability map has been used to mark accumulation points on the down streams as potential spots of water storage. In addition, site suitability of artifcial structures for RWH consisting of farm ponds, check dams and percolation tanks has also been assessed, showing 3.2%, 3% and 4.5% of the total area as a ft for each of the structure, respectively. The derived suitability will aid policy makers to easily determine potential sites for RWH structures to store water and tackle acute paucity of water in the area.