Rainwater Harvesting Performance Research Articles

Improvement of simulating sub-daily hydrological impacts of rainwater harvesting for landscape irrigation with rain barrels/cisterns in the SWAT model

Rain barrels/cisterns, a popular type of low impact development (LID) practice, can restore urban hydrological processes and decrease municipal water use by harvesting roof runoff for later use, such as landscape irrigation. However, tools to assist decision makers in creating efficient rainwater harvesting and reuse strategies are limited. This study improved the Soil and Water Assessment Tool (SWAT) in simulating the subdaily hydrological impacts of rainwater harvesting for landscape irrigation with rain barrels/cisterns, including the simulation of rainwater harvesting with rain barrels/cisterns, rainwater reuse for auto landscape irrigation, evapotranspiration, initial abstraction, impervious area, soil profile, and lawn management operation. The improved SWAT was applied in the urbanized Brentwood watershed (Austin, TX) to evaluate its applicability and investigate the impacts of rainwater harvesting and reuse strategies on the reductions and reduction efficiencies (reductions per volume of rain barrels/cisterns implemented) of field scale runoff (peak and depth) and watershed scale streamflow (peak and volume) for two storm events. Scenarios explored included different sizes of rain barrels/cisterns, percentages of rooftop areas with rain barrels/cisterns implemented, auto landscape irrigation rates, and landscape irrigation starting times. The performance of rainwater harvesting and reuse strategies, which is determined by features of fields, watersheds, and storm events, varied for different reduction goals (streamflow or runoff, and peak or depth/volume). For instance, the scenario with rain barrel/cistern sizes of 7.5 mm (design runoff depth from treated roof area) and the scenario with 10% of suitable area implemented with rain barrels/cisterns provided the highest peak streamflow reduction efficiency and total streamflow volume reduction efficiency at the watershed scale, respectively for the smaller storm event. To achieve sustainable urban stormwater management, the improved SWAT model has enhanced capability to help stakeholders create efficient rainwater harvesting and reuse strategies to reduce field scale runoff and watershed scale streamflow.

Influence of rainfall and design criteria on performance of rainwater harvesting systems placed in different Brazilian climatological conditions

ABSTRACT Using rainwater harvesting (RWH) system is influenced by socioeconomic, environmental and technical factors. This work presents as analysis of the influence of the rainfall time series characteristics and design criteria on RWH performance of five Brazilian capitals with different climatic characteristic: Goiânia, João Pessoa, Manaus, Porto Alegre and São Paulo. The analysis combined different rooftop areas, storage volumes and the indoor and outdoor demands. Rainfall temporal discretization and the types of demands were the most important characteristics when assessing RWH reliability. Daily rainfall data were suitable for sizing the RWH, the time series length influenced the sizing of larger storage volumes, and the RWH efficiency was not significantly affected by the first-flush. Toilet flushing and the irrigation demands had the greatest impact on RWH performance. The greatest potentials for the implementation of RWH were observed for Porto Alegre, because of well distributed rainfall throughout the year, and for Manaus owing to higher annual volumes of precipitation. These results highlight relevant aspects that must be observed during the conception and design of RWH, complementing the guidelines provided in the Brazilian technical standards.

Economic Evaluation of Rainwater Harvesting and Conservation (RWHC) Technologies for Sweet Potato Cultivation in Sierra Leone

A field trial was conducted to evaluate the economic performance of rainwater harvesting and conservation (RWHC) technologies for sweet potato cultivation in Sierra Leone during five intensive cropping seasons (2014 second – 2016 second cropping season) at the on-station research site of the Njala Agricultural Research Centre. The experiment was laid out in a randomized complete block design in three replications following a factorial combination of two levels of mulch (no mulch and mulch) and three levels of RWH structures (open ridge, tied ridge and arch ridge). Six RWHC technologies evaluated: open ridge without mulch (OR-M), open ridge with mulch (OR+M), tied ridge without mulch (TR-M) and tied ridge with mulch (TR+M), arch ridge without mulch (AR-M) and arch ridge with mulch (AR+M). Profitability (gross margin, net income and breakeven), investment (NPV, IRR and BCR) and sensitivity analyses (25% root yield loss and 10% fall in the market price of sweet potato roots) were used to evaluate the economic performance of the RWHC techniques. The TR+M (SLL 2,091,280) had the highest net income followed by the AR-M (SLL 693,640) and AR+M (SLL 2,218,160) RWHC technologies. The traditional OR-M was not profitable (SLL -2,487,760) for sweet potato cultivation. Based on the cost of production, the OR-M, OR+M, and TR-M RWHC technologies require a root yield increase of 50.5%, 3.0% and 35.4% to breakeven. The AR+M had the highest and positive net seasonal cash flow returns throughout the five cropping seasons. The breakeven point on the net season seasonal cash flow returns for the TR+M, AR-M and OR+M RWHC technologies was in the 2015 main cropping season. At discount rates of 10%, 15%, 20% and 25% the highest NPV was obtained from the AR+M followed by the TR+M and AR-M RWHC technologies. The highest IRR was obtained from the AR+M (111%) followed by TR+M (84%) and AR-M (61%). The AR+M, TR+M and AR-M RWHC technologies had benefit-cost ratios greater than 1. Under uncertain conditions of 25% root yield loss and 10% fall in the market price of sweet potato roots, the AR+M and TR+M are the most profitable RWHC technologies that could be invested in. These technologies should, therefore, be promoted for adoption through on-farm trials in order to enhance intensive sweet potato cultivation on upland gravelly soils in Sierra Leone.

Evaluation of rainwater harvesting performance for water supply in cities with cold and semi-arid climate

Abstract In this study, the performance of rainwater harvesting (RWH) was assessed in terms of potential applicability for rainwater saving and non-potable water supply. Rainwater collecting from roofs of buildings was simulated in two cities with cold and semi-arid climate, namely Qazvin and Sanandaj. Rainfall statistics, information on the storage tank size, building roof areas and water demand (non-potable) were obtained. Buildings with roof areas of 100 m2 to 300 m2 were considered for the present study. It can be concluded that for cities located in cold and semi-arid climates, at least 60% of non-potable water can be supplied from roofs with a large area, a minimum 16% and maximum 70% for a low roof area, a minimum 8% and maximum 44% of the days per year from harvested rainwater. It is also found that for cities located in cold and semi-arid climates, it is possible to achieve at least 70% of non-potable water from large surface roofs. For the studied cities, with increasing tank size (1,000 to 5,000 L) rainwater saving was tangible for the same roof areas.

Indicadores de consumo de água e análise comparativa entre o aproveitamento de águas pluviais e o reúso de águas cinzas em edificações de ensino do Campus Darcy Ribeiro - UnB

Este trabalho teve como objetivo caracterizar os usos-finais de água em edificações de ensino superiordo Campus Universitário Darcy Ribeiro da Universidade de Brasília e, com isso, realizar uma análisecomparativa do desempenho de sistemas de aproveitamento de águas pluviais (AAP) e de reúso deáguas cinzas (RAC). Para tanto, o estudo se dividiu em três etapas. Na primeira etapa, indicadores deconsumo predial foram gerados com base no consumo faturado, área construída e população de cadaedificação analisada. Usos-finais de água foram estimados por meio de questionários e entrevistassemiestruturadas. Na segunda etapa, foram realizadas uma série de simulações para verificar aeconomia de água para diferentes sistemas AAP e RAC baseando-se em três cenários de usos nãopotáveis: i) Irrigação e lavagem de pisos (Cenário 1); ii) Descarga sanitária (Cenário 2); e iii) Irrigação,lavagem de pisos e descarga sanitária (Cenário 3). Na terceira etapa, foi realizada uma análisecomparativa do desempenho dos sistemas na redução do consumo de água. Os resultados mostraramque, para o Cenário 1, ambos os sistemas conseguem suprir toda a demanda de água. Porém, a maioriados sistemas não são capazes suprir toda a demanda dos Cenários 2 e 3. Em geral, o aproveitamentode águas pluviais apresentou um melhor desempenho, promovendo economia de 137 a 19.510 m3/ano,dependendo da grandeza da edificação.

County‐Scale Rainwater Harvesting Feasibility in the United States: Climate, Collection Area, Density, and Reuse Considerations

AbstractRoof rainwater harvesting (RWH) has the potential to augment water supplies for urban and suburban uses throughout the United States (U.S.). Studies of the performance of RWH at the building and city scales in the U.S. are available, but a countrywide overview of the potential performance of RWH at the county scale has not been done before. Three approaches were taken: (1) assess the viability of RWH in terms of the rainfall that could be captured in relation to the water demand in each county (excluding agriculture), (2) evaluate the performance of a “typical” domestic RWH system across all counties with metrics related to its ability to supply the potable and nonpotable demand, and (3) evaluate the effect of adding a 50% rainwater reuse component to the analysis. We find RWH could be a viable supplemental water source in the U.S., particularly in counties of the Pacific Northwest, Central, and Eastern regions (percent demand covered >50%). Low population density counties have the potential to meet their annual water needs with RWH, while high‐density counties could only source a small portion (~20%) of their annual demand with RWH. Typical RWH systems in counties in the Central and Eastern U.S. performed better than in Western counties. Adding a reuse component can be a key factor in making RWH attractive in many areas of the country. This work can inform future water infrastructure investment and planning in the U.S.

Performance of rainwater harvesting system based on roof catchment area and storage tank capacity

Increasing population growth has created problems in water resources. Natural water resources become progressively more expensive and difficult to develop. In addition, it is also becoming increasingly polluted and difficult to obtain. Many countries shown a resurgent interest in the use of rainwater harvesting (RWH) technique to overcome these problems. There are several factors that will influence the RWH performance, such as the rainfall, catchment area, storage tank capacity, and water demand. The performance parameter determines by the volumetric reliability, time reliability, and yield. The RWH system used in this study is a simple RWH system that utilizes roof as a catchment area, pipes as a distribution system and tank as a storage. An analysis is carried out to investigate the effect of altering the large of the catchment area and storage tank capacity to the RWH system performance parameters. A suitable behavioral model based on the water balance method is implemented to evaluate the inflow, outflow, and the storage volume. Results demonstrate that with up to 15 years daily rainfall data in 15 cities in Indonesia, the most influential parameters on the performance of RWH system is the time reliability.

Rainwater harvesting for supplemental irrigation of onions in the southern dry lands of Ethiopia

Agricultural water scarcity is a major limiting factor for crop production in dry land regions of sub-Saharan Africa (SSA). Despite notable efforts of developing macro-catchment rainwater harvesting (RWH) techniques, few studies have evaluated the performance of RWH for deficit supplemental irrigation of crops. We examine the agro-meteorological risks such as late onset, early cessation, overall low rainfall amounts and long dry spells during the growing season and evaluate the potential of macro-catchment RWH for supplemental irrigation of onion in the southern dry lands of Ethiopia. Field experiments were undertaken during 2012 and 2013 to evaluate the effects of 50% ETc, 75% ETc and 100% ETc irrigation levels on yield and water productivity of onion during dry and wet seasons. The harvestable yield and water productivity of onion under 75% ETc irrigation were not significantly lower than that under 100% ETc irrigation during both the dry and wet seasons. Thus, deficit supplemental irrigation of onion at 75% ETc can be implemented with macro-catchment RWH to reduce the risks of crop failure and significant yield declines in dryland areas.

A water harvesting model for optimizing rainwater harvesting in the wadi Oum Zessar watershed, Tunisia

Rainwater harvesting (RWH) techniques have been adapted in arid and semi-arid regions to minimise the risk from droughts. The demand for water has increased but water resources have become scarcer, so the assessment and modelling of surface water related to RWH in catchments has become a necessity. An understanding of the hydrological processes at the sub-catchment level is generally lacking, and little attention has been given to the assessment of RWH after implementation. The objective of this study was to develop a simple but generally applicable water-harvesting model and test it at sub-catchment level to evaluate and optimize the performance of RWH under different design and management scenarios. The model was applied to rainfall data for 1980–2004 in 25 sub-catchments of the watershed of Wadi Oum Zessar (south-eastern Tunisia). The performance and analysis of RWH in three types of years (dry, normal, and wet) are presented and discussed. This study emphasises the advantages of simulating long-term water balances at the sub-catchment level for improving our understanding of hydrological processes in the RWH system and provides several solutions for optimizing RWH performance in various scenarios. Changing the spillway heights together with the flow directions had a significant impact on the performance of RWH by making 92% of all sub-catchments supply sufficient water for crop requirements, compared to 44% of the sub-catchments in case of no changes.

Harvesting rooftop runoff to flush toilets: Drawing conclusions from four major U.S. cities

As it provides the simultaneous benefits of reducing the demand for potable water and the generation of water runoff, rainwater harvesting (RWH) has received increasing attention from urban water managers in the past decades. This study employs a mass balance based method to estimate RWH performance for four large metropolitan areas of the United States, namely New York City, Philadelphia, Chicago, and Seattle. Geospatial analysis is used in concert with climatic records to characterize the cityscape and climatic patterns of each city and evaluate the RWH systems performance both in terms of potable water savings and roof runoff reductions. The analysis indicates that typical urban rainwater harvesting setups, consisting of a 100m2 roof connected to a 5m3 storage volume, would be able to reduce potable water demand by over 65% in all cities while contextually reduce roof runoff generation by over 75%. Small differences in performance are observed among cities due to differences in precipitation patterns, typical roof area, and population density. Furthermore, an evaluation of the total water savings and runoff reduction for the application of RWH practices at maximum build out for all four study cities is provided, and the sensitivity of our estimates of performance to precipitation patterns and to the systems’ operating algorithm is also analyzed and discussed.

Field report: Large-scale school rainwater harvesting systems: a pilot study in Nyanza Province, Kenya

In schools where water supply is either unavailable or insufficient, rainwater harvesting (RWH) systems may be a low-cost solution. We piloted large-scale RWH systems in rural primary schools in Nyanza Province, Kenya to investigate the sustainability of these systems several years post-implementation. This paper discusses the main findings of our pilot and, to our knowledge, is the only published study on school RWH performance in a low-income setting.

Assessment of residential rainwater harvesting efficiency for meeting non-potable water demands in three climate conditions

Global demand for clean water supplies is on the rise due to population growth. This is also true in most cities of Iran. Non-conventional water resources must be developed to partially offset the increasing demand. In this study, the applicability and performance of rainwater harvesting (RWH) systems to supply daily non-potable water were assessed. Storage of rain falling on the roofs of residential buildings and directed into installed tanks was simulated in three cities of varying climatic conditions, namely Tabriz (Mediterranean climate), Rasht (humid climate), and Kerman (arid climate). Daily rainfall statistics for a period of 53 years as well as the information on the contributing roof area, available tank volumes and non-potable water demand were collected in each city. Typical residential buildings with roof areas of 60, 120, 180 and 240m2 with an average of four residents in each house were considered for the study. According to the results in humid climate, it is possible to supply at least 75% of non-potable water demand by storing rainwater from larger roof areas for a maximum duration of 70% of the times. For roofs with small surface area, the supply meets 75% of non-potable water demand for a maximum duration of 45% of the times. Moreover, for Mediterranean climate, it is possible to supply at least 75% of non-potable water demand in buildings with larger roof areas for a maximum duration of 40% of the times. It is also found that in arid climate, similar duration is only 23% of the times.