A new rainwater harvesting and recycling system for transforming sloping land into terraced farmland

Transforming sloping land into terraced land is an effective approach to cope with the problems including farmland shortage and severe soil erosion.This paper introduces a new system based on rainwater harvesting and recycling technology,which may effectively improve farmland productivity rainwater use efficiency and reduce water and fertilizer inputs.The new system consists of three subsystems：1） A plough layer with the dual function of crop cultivation and rainwater harvesting; 2） A tank below the plough layer for storing water; 3） An irrigation-drainage subsystem.The plough layer and the storage tank,both treated for reducing seepage,are connected through the irrigation and drainage system.Results showed that,compared with the traditional paddy fields,rice evapotranspiration（ and crop coefficient） in the test field remained at a similar level,while the irrigation amount was reduced by 44.3% under the condition of basin irrigation,and the drainage amount decreased by 86.6%,and the non-point source pollution was reduced to 67.7%~87.9%,and the rainwater utilization efficiency increased by 30% and reached 95.4%,and crop yield of middle-season rice reached 9,975 kg/hm2,which was only 0.4% lower than that in the traditional paddy field in the terms of dry matter.The new technology sheds light on new possibilities for transformation of hilly sloping land.     

三种主要干扰造成中国森林植被向大气中的碳排放量

对重要干扰过程导致森林植被向大气中的碳排放量进行评估,对于合理评估森林碳汇功能及其在应对全球气候变化中的作用是有重要意义的。本文基于有关森林干扰发生情况的林业统计资料和有关干扰引起生物量C转移过程与比例的假设条件,估算了近20年来采伐、火灾与病虫鼠害三种主要干扰每年从森林植被直接排放到大气中的C量。结果表明,近20年来,中国森林遭受了比较强烈的采伐、火灾与病虫鼠害干扰,并且这三种干扰在进入21世纪后有着比较明显的增加趋势。相应地,在1990-2009年间,采伐、火灾与病虫鼠害的C排放量年均分别为3425.16万tC、161.29万tC、428.80万tC,合计为4015.24万t。三种干扰的总C排放量在1990-1999年间年均为3079.40万t,在2000-2009年间年均为4951.09万t。从不同森林类型分布区的排放来看,中国森林主要干扰的年均C排放量及其年代际变化呈现比较明显的区域特征。干扰对中国森林碳平衡有着重大影响,针对干扰的森林管理可能具有较大的增汇潜力,并且在未来有关森林与陆地生态系统碳收支的模型研究中需考虑主要干扰的影响。     

How important is the selection of computational analysis method to the accuracy of rainwater tank behaviour modelling?

As the concept of sustainable urban water management is incorporated into the practice of urban water resource managers, actions, such as the utilization of roof runoff via rainwater tanks, which have multiple benefits, are increasingly being built into urban water systems. Modelling tools are frequently used to predict the yield from rainwater tanks and to estimate the storage capacity required to achieve a given potable supply reduction level, with these estimates used in both urban water resources policy development and engineering design. Therefore, it is important that the accuracy of commonly used models is understood. This paper investigates the impact of computational time step, computational operating rule, initial storage level, and the length of simulation period on the accuracy of the storage–yield–reliability relationship calculated using a simple rainwater tank behaviour model. Four time steps (ranging from 6 min to 24 h), two operational rules (supply before spillage and supply after spillage), two initial storage level states (empty and full), and three simulation periods (50 years, 10 years and 1 year) were applied to a wide range of rainwater tank system configurations and three different locations in Australia. It was found that the supply‐after‐spillage computational operating rule is preferable, while the ratio of the average demand volume in a single computational time step divided by the storage capacity (ΔD/S) can be used to assess whether a given combination of demand, storage, inflow, and computational time step will provide long‐term yield estimates that are within ± 5% of the values produced by a simulation that used a 50‐year time series of climate, 6‐min time step, and a supply‐after‐spillage operational rule (50‐6‐YAS). Copyright © 2007 John Wiley & Sons, Ltd.     

The impact of peat harvesting and natural regeneration on the water balance of an abandoned cutover bog,Quebec

Harvested sites rarely return to functional ecosystems after abandonment because drainage and peat extraction lower the water table and expose relatively decomposed peat, which is hydrologically unsuitable for Sphagnum moss re‐establishment. Some natural regeneration of Sphagnum has occurred in isolated pockets on traditionally harvested (block‐cut) sites, for reasons that are poorly understood, but are related to natural functions that regulate runoff and evaporation. This study evaluates the water balance of a naturally regenerated cutover bog and compares it with a nearby natural bog of similar size and origin, near Riviere du Loup, Quebec. Water balance results indicated that evapotranspiration was the major water loss from the harvested bog, comprising 92 and 84% of total outputs (2·9 mm day^?1) during the 1997 and 1998 seasons, respectively. Despite denser tree cover at the harvested site, evapotranspiration from the natural bog was similar, although less spatially variable. At the harvested site, evaporative losses ranged from 1·9 mm day^?1 on raised baulks and roads to 3·6 mm day^?1 from moist surfaces with Sphagnum. Although about half of the ditches were inactive or operating at only a fraction of their original efficiency, runoff was still significant at 12 and 24% of precipitation during the 1997 and 1998 study seasons, respectively. This compares with negligible rates of runoff at the natural bog. Thus the cutover bog, although abandoned over 25 years ago, has not regained its hydrological function. This is both a cause and effect of its inability to support renewed Sphagnum regeneration. Without suitable management (e.g. blocking ditches), this site is not likely to improve for a very long time. Copyright © 2001 John Wiley & Sons, Ltd.     

The effect of forest cover on peak flow and sediment discharge—an integrated field and modelling study in central–southern Chile

An integrated field and modelling study was carried out on the 35‐ha La Reina catchment, Chile, to test the hypothesis that the effect of forest cover on flood peaks becomes less important as the size of the hydrological event increases. Meteorological and discharge data were measured at the catchment before and after the pine plantation that covered 80% of the catchment area was logged. Analysis of the measured response of the catchment provides support for the hypothesis but is not conclusive. Therefore, modelling of the catchment using 1000 years of generated rainfall data representative of the current conditions was carried out for the forested and logged states. The simulations show that the absolute difference in discharge between the two cases remains approximately constant as the discharge increases: thus as a percentage of discharge it decreases. This relative convergence appears to become significant at return periods of greater than approximately 10 years. Tests with different hypothetical soil depths for the forested and logged catchments show an absolute convergence in discharge between the two cases for shallow soils and no convergence for deep soils. Sediment transport simulations show that forest cover provides a clear benefit in protecting the soil from erosion. Copyright © 2010 John Wiley & Sons, Ltd.     

Morphodynamic research challenges for braided river environments: Lessons from the iconic case of New Zealand

Pressures on braided river systems in New Zealand are increasing due to anthropogenic stresses such as demand for irrigation water, braidplain conversion to farmland and invasive vegetation, as well as extreme natural events associated with earthquakes and climate change. These pressures create issues around preserving braided river physical environments and associated ecosystems, and managing hazards such as floods, aggradation and erosion. A need for more robust understanding and quantification of braided river morphodynamic processes underpins many of these issues. Here, we present eight morphodynamic research challenges to service this need. The first four research challenges relate to managing aggradation-related flooding hazards; the last four address issues stem largely from recent dairy expansion, which has created huge pressure to take land and irrigation water from the alp-fed braided rivers and to alter flow regimes at their mouths. Hāpua, the freshwater lagoons found where most braided rivers meet the coast, show complex morphodynamic behaviour in response to the interplay of river and coastal processes, and their special ecosystems are sensitive to river flow and sediment load changes. We discuss how physical laboratory experiments and novel numerical modelling can help to understand the morphological processes braided rivers undergo, and we show how those research advances could inform planning and legal decisions to regulate land rights and irrigation water allocation on New Zealand's braidplains. We illustrate these environmental and engineering issues and research challenges with examples from the Kowhai, Waiho, Waiau, Rangitata and Hurunui Rivers. © 2020 John Wiley & Sons, Ltd.     

An octo-generator for energy harvesting based on the piezoelectric effect

A renewable energy harvester using the piezoelectric effect is developed for the ocean tidal and wind flow. The harvester is made of connected driving blades to an octo-generator, which has a rotator with n blades and a stator attached by eight mass-spring-piston-cylinder-piezoelectricity devices. The resonance and force magnification are utilized to increase the power output of the harvester. A corresponding mathematical model is developed to calculate the root mean square of the generated electric power. The simulation results indicate that the generated power is largely enhanced when the near-resonant condition is established. The power increases with increases in the magnetic flux density, the large-to-small diameter ratio of the cylinder, the size of magnetic bar face, and decreases in the gap between two magnetic faces and the size of the piezoelectric bar face. A generated power of 5 kW is realized by the harvester working under an ocean tidal speed, V = 1.75 m/s, and its geometric and material properties of driving length L = 7.5 m, spring constant k_v = 65000 N/m, gap between the two magnets s = 0.0015 m, large to small diameter ratio of the cylinder z = 6, and magnetic flux density Br = 1.45 T.     

Assessment of overland flow variation and blue water production in a farmed semi-arid water harvesting catchment

Upgrading agriculture in semi-arid areas and ensuring its sustainability require an optimal management of rainfall partition between blue and green waters in the farmed water harvesting catchment. The main objective of this study is to analyze the influence of heterogeneous land use on the spatial and temporal variation of rainfall partitioning and blue water production within a typical farmed catchment located in north-eastern Tunisia. The catchment has an area of 2.6 km² and comprises at its outlet a dam, which retains the runoff water in a reservoir. Overland flow and soil water balance components were monitored during two cropping seasons (2000/2001 and 2001/2002) on a network of eleven plots of 2 m² each with different land use and soil characteristics. The hydrological balances of both the catchment and reservoir have been monitored since 1994.Observed data showed a very large temporal and spatial variability of overland flow within the catchment reflecting the great importance of total rainfall as well as land use. During the 2001/2002 season the results showed a large variation of the number of observed runoff events, from 27 to 39, and of the annual overland flow depths, from 8 mm (under vineyard on calcaric cambisols) up to 43 mm (under shrubs-pasture on haplic regosols), between the plots. The annual runoff amounts were moderate; they always corresponded to less than 15% of the annual rainfall amount whatever the observation scale. It was also observed that changes in land use in years with similar rainfall could lead to significant differences in blue water flow. An attempt for predicting the overland flow by the general linear regression approach showed an r² of 31%, the predictors used are the class of soil infiltration capacity, the initial moisture saturation ratio of the soil surface layer and the total rainfall amounts.These experimental results indicate that the variation in land use in a semi-arid catchment is a main factor of variation in soil surface conditions and explain the major role played by the former on hydrological behavior of the upstream area and on rainfall partition between overland flow and infiltration. Therefore, to predict the water harvesting capacities in terms of blue water production of a farmed catchment in semi-arid areas it seems essential to consider precisely its land use and its temporal evolution related to management practices.     

Soil losses due to potato and sugar beet harvesting in NE China

The study of soil loss due to crop harvesting (SLCH) started only recently in soil erosion research. It describes the mass of adhering soil, soil clods and rock fragments that is lost from arable land during the harvesting of crops such as potato, sugar beet, sweet potato and cassava. Some research on mechanized agriculture in Europe revealed that soil loss rates due to crop harvesting can be comparable to water and tillage erosion rates. However, little is known about soil losses caused by manually harvested crops in other parts of the world. This study investigated SLCH for potato and sugar beet plots on farmer's fields spread over four regions in northeast China where harvesting is carried out by hand. Soil losses for sugar beet were on average 1·0 Mg/ha/harvest, ranging from 0·2 to 1·9 Mg/ha/harvest, and SLCH for potato ranged from 0·2 to 3·0 Mg/ha/harvest with an average of 1·2 Mg/ha/harvest. Soil moisture content, average root mass and plant density could explain 45 to 67 per cent of the variability of SLCH for sugar beet. The effect of soil texture was the opposite to findings of other studies, which could be attributed to the strong correlations among the variables and to the effect of the harvesting operator. SLCH variability for potatoes could best be explained by soil texture. SLCH for sugar beet was much lower than European SLCH values for this crop, which can be explained by differences in harvesting technique and agronomic practices. SLCH for potato was comparable to soil losses measured in Belgium, especially if clods are removed on the harvesting machine. However, clay contents of the soils were larger in this study and soil losses were lower than in Belgium for comparable clay contents. Although SLCH is not the dominant soil erosion process in NE China, it contributes to overall soil loss rates, which have already exceeded their critical tolerance limits in this region. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluation of the on-site impact of water harvesting in southern Tunisia

Water harvesting techniques (WHT) play an important role in water resources conservation in (semi-) arid environments. However, the impacts of WHT are not clearly understood. This paper presents a method to measure increased water availability to olive (Olea europeae) trees grown on the terraced area of a traditional WHT site in southern Tunisia (jessr) and to translate these measurements into effects on yield. Although the WHT were shown to greatly enhance possibilities for olive growing, yields remain dependent on water supply (rainfall+run-on) in spring. Critical factors in the method described are the maximum available soil water capacity (ASW_max), crop and yield response factors (kc, ky_veg and ky_fruit) and the yield consistency index (YCI). Detailed accounts are presented for the costs and benefits of jessr construction and olive production, and the WHT are evaluated using cost-benefit analysis. Difficulties and assumptions are discussed and it is concluded that on-site effects alone might not justify investing in the construction of WHT.