Downstream End Research Articles

Dynamic flood wave routing in prismatic channels with hydraulic and hydrologic methods

AbstractTime-dependent, unsteady flow has been studied in prismatic open channels with symmetric trapezoidal and triangular cross sections and small bottom slope. The St Venant equations without lateral inflow have been discretized in explicit as well as in implicit form and solved numerically, for unsteady, subcritical flow. The inflow hydrograph used can be applied for different flood events by adjusting its parameters accordingly. The results presented are derived from the explicit schemes Lax-Diffusive, MacCormack, Lambda as well as the implicit Preissmann scheme, and are compared to those from the Muskingum-Cunge method and the widely used commercial software HEC-RAS. The peak flow computed by the Lax-Diffusive scheme was reduced at the downstream end of the channel and the arrival time of the peak increased if compared to the other methods. The Muskingun-Cunge method forecasted the shortest peak flow arrival time at the downstream end cross section. Mass conservation computed from inflow and outflow hydrographs has been confirmed, since the maximum error did not exceed 2.60%. All codes were implemented in house using Matlab®.

Unit bar architecture in a highly‐variable fluvial discharge regime: Examples from the Burdekin River, Australia

AbstractUnit bars are relatively large bedforms that develop in rivers over a wide range of climatic regimes. Unit bars formed within the highly‐variable discharge Burdekin River in Queensland, Australia, were examined over three field campaigns between 2015 and 2017. These bars had complex internal structures, dominated by co‐sets of cross‐stratified and planar‐stratified sets. The cross‐stratified sets tended to down‐climb. The development of complex internal structures was primarily a result of three processes: (i) superimposed bedforms reworking the unit bar avalanche face; (ii) variable discharge triggering reactivation surfaces; and (iii) changes in bar growth direction induced by stage change. Internal structures varied along the length and across the width of unit bars. For the former, down‐climbing cross‐stratified sets tended to pass into single planar cross‐stratified deposits at the downstream end of emergent bars; such variation related to changes in fluvial conditions whilst bars were active. A hierarchy of six categories of fluvial unsteadiness is proposed, with these discussed in relation to their effects on unit bar (and dune) internal structure. Across‐deposit variation was caused by changes in superimposed bedform and bar character along bar crests; such changes related to the three‐dimensionality of the channel and bar geometry when bars were active. Variation in internal structure is likely to be more pronounced in unit bar deposits than in smaller bedform (for example, dune) deposits formed in the same river. This is because smaller bedforms are more easily washed out or modified by changing discharge conditions and their smaller dimensions restrict the variation in flow conditions that occur over their width. In regimes where unit bar deposits are well‐preserved, their architectural variability is a potential aid to their identification. This complex architecture also allows greater resolution in interpreting the conditions before and during bar initiation and development.

Linear model of water movements for large-scale inverted siphon in water distribution system

Abstract This paper proposes a linear model that relates the pressure head variations at the downstream end of an inverted siphon to the flow rate variations at two ends. It divides the pressure head variations in the inverted siphon into low-frequency part and high-frequency part. The two parts are caused by the deformation of the siphon wall and the reflection of acoustic wave, respectively. In order to build a simplified relation between wall deformation and low-frequency pressure head variations, the Preissmann slot method (PSM) is adopted in this paper. The linear model can also be used in other forms of structures, such as pipes and tunnels, where a pressurized flow condition is present. In comparison with simulation results using the finite volume method, the linear model shows an L2 norm of 0.177 for a large-scale inverted siphon and 0.044 for a PVC pipe. To this end, the linear model is adopted to model a large-scale inverted siphon in a virtual water delivery system. Simulation results show that the inverted siphon can reduce water fluctuations. An equation to quantify this effect is proposed based on the linear model.

An analysis of core functions offered by software packages aimed at the supply chain management software market

The Purpose of this paper is to investigate the use of software packages (SP) aimed at the supply chain management (SCM) market. The aim is to analyse and classify the range of software functionalities offered by a variety of SCM-SPs currently in the market. This is important to gain an insight into the current and future trend in demands for applications of information & communication technology (ICT) for SCM. The study assumes that most ICT hardware used for SCM processes will require software interaction. Thus study of the variety of functionalities offered by SCM-SPs will provide insights into the use of ICT for SCM.In this paper, literature on SCM and applications of ICT for SCM is used to develop a SCM software function classification map (SCM-SFC map) for SPs aimed at the SCM market. The SCM-SFC map breaks down the SCM process into four key functional areas: sales management, relationship management, planning & production management and flow management. Each key functional area is further broken down into an overall of sixteen areas of core software functions. We then analysed 242 SCM-SPs currently in the market. We identified a total of 1295 software functionalities present in the 242 SCM-SPs. Each of these functionalities was then classified within the taxonomy of the SCM-SFC map. The results were used to identify areas of high and low intensity of core software functions and key SCM functionalities present in SCM-SPs analysed.The main finding indicated that flow management to coordinate supply chain operations consisted nearly half of functionalities offered by SCM-SPs. ICT is particularly useful in the SCM sector for prevention of bullwhip and cash flow bullwhip effects. The study also indicates a potential growing trend towards using ICT for forecasting at the upstream end of the supply chain. At the downstream end of the supply chain, the study suggests that ICT could increasingly be used for online retailing through software functionalities that enables integration with online platforms to allow E-commerce processes. The research provided the SCM-SFC map as a new means to categorise functionalities offered by SCM-SPs. Analysing SCM-SPs and listing their functionalities within the taxonomic framework of the SCM-SPs was also a novel approach at investigating the use of ICT for SCM. This approach can be used as a means to regularly provide insights into market changes in terms of demands from ICT for SCM practices.

Determining hydraulic characteristics in laterals and drip irrigation systems

Evaluation methods for functioning drip irrigation units are proposed to determine the hydraulic characteristics of emitters and pipelines. The aim of the study was to characterize the discharge curve of the emitters, their coefficient of variation, and the head losses in laterals and submains. In the laboratory, four laterals were tested under a wider range of pressure heads than the typical values of field installations. In additional, a field irrigation unit was evaluated. The discharge curve and coefficient of variation were determined in the unit with an accuracy similar to that obtained from laboratory experiments. For self-compensating emitters, a constant flow rate above the lower limit of the compensating range and an orifice-type discharge curve below that limit are proposed. For non-compensating emitters, an orifice-type discharge curve, with exponent x = 0.5, except for specific cases, is proposed. The manufacturing coefficient of variation was independent of pressure and relatively low for all the analysed emitters. Regarding the parameters of the local head losses, the equivalent length le presented values more independent of the flow than coefficient K. For the characterisation of laterals with self-compensating emitters, it is recommended to measure with the downstream end open to reduce the uncertainty in the experiments. The results show that the unit can be operated so that the average discharged flow and the uniformity can be matched just controlling the pressure head at upstream end point of the unit.

Visualization Tests on Variation of Scour Front under a Pipeline in Steady Currents

The intersection of the span shoulder and the scour hole under a pipeline, also called the scour front, can affect the scour hole extension rate and the bearing capacity of the span shoulder, which is associated with pipeline spanning and failure. Studies on scour front evolution are limited due to technical restrictions. In this study, visualization experiments on three-dimensional scour under a pipeline in steady currents were performed to reveal the evolution of the scour front at the beginning of scour process, and the parametric effects on the scour front pattern. The angle of scour front witnessed a steady drop at the start of the scour development process and fluctuated gently thereafter. This can be attributed to the decrease in the blockage effect over time. A gravitational movement was observed on the downstream end of the scour front, which is associated with the variation of fluid pressure along the scour front. The scour front pattern was described by the angle between the scour front and the streamwise direction. Parametric analysis showed that the averaged scour front angle climbs as the Froude number increases and the pipeline embedment drops. This phenomenon can be expounded by the intensified flow deflection near the span shoulder due to the enhancement of the pipeline blockage effect, caused by the ascending Froude number and descending pipeline embedment. The results of this study can be adopted in future mechanism investigations on the scour hole propagation rate and the failure analysis on the span shoulder.

Hydraulic transients in pipelines due to various valve closure schemes

In this study, the hydraulic transient in a pipeline model was considered by utilizing the method of characteristics. The pipeline conveys water from the upstream reservoir to the downstream one, while a valve was set at the downstream end of it. The effect of sudden, linear and stepwise valve closure schemes were analysed by employing a stainless-steel pipe and a ductile pipe. Sudden valve closure was noted to generate higher-pressure transients than linear and stepwise schemes. As the closure time period increases, the value of the maximum pressure transient decreases, in both linear and stepwise arrangements. The transient pressure was perceived to be higher in stainless-steel pipe than in ductile one, in three closure schemes. The simulations were performed by a purpose-developed MATLAB code.

Wetland Management Strategy to Reduce Mercury in Water and Bioaccumulation in Fish.

Wetland environments provide numerous ecosystem services but also facilitate methylmercury (MeHg) production and bioaccumulation. We developed a wetland-management technique to reduce MeHg concentrations in wetland fish and water. We physically modified seasonal wetlands by constructing open- and deep-water treatment cells at the downstream end of seasonal wetlands to promote naturally occurring MeHg-removal processes. We assessed the effectiveness of reducing mercury (Hg) concentrations in surface water and western mosquitofish that were caged at specific locations within 4 control and 4 treatment wetlands. Methylmercury concentrations in wetland water were successfully decreased within treatment cells during only the third year of study; however, treatment cells were not effective for reducing total Hg concentrations. Furthermore, treatment cells were not effective for reducing total Hg concentrations in wetland fish. Mercury concentrations in fish were not correlated with total Hg concentrations in filtered, particulate, or whole water; and the slope of the correlation with water MeHg concentrations differed between months. Fish total Hg concentrations were weakly correlated with water MeHg concentrations in April when fish were introduced into cages but were not correlated in May when fish were retrieved from cages. Fish total Hg concentrations were greater in treatment wetlands than in control wetlands the year after the treatment wetlands' construction but declined by the second year. During the third year, fish total Hg concentrations increased in both control and treatment wetlands after an unexpected regional flooding event. Overall, we found limited support for the use of open- and deep-water treatment cells at the downstream end of wetlands to reduce MeHg concentrations in water but not fish. We suggest that additional evaluation over a longer period of time is necessary. Environ Toxicol Chem 2019;38:2178-2196. Published 2019 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America..

Influence of Intermittence and Pressure Differentials in Hydrogen Sulfide Concentration in a Gravity Sewer

The work presented herein was carried out to assess the effect of intermittent pumping events in sewer headspace pressure differentials, as well as their relationship with hydrogen sulfide gas concentration. A full scale gravity sewer in Portugal, located downstream of several pumping stations, was used as the guiding case study. Under normal system operation, pressure difference between the outside atmosphere and the sewer headspace seemed to influence the in and out-gassing of gas pollutants emitted through the venting stack. Wastewater pumping cycles generated maximum pressure differentials of roughly 100 Pa, which in turn originated maximum air velocities of 1.76 m s−1 exiting the venting stack. Each pumping event was followed by a pressure drop of about 50 Pa, quickly attaining null concentrations of H2S at the venting stack. A statistically significant relationship between pressure differentials and air exit velocity was observed, which allowed obtaining an empirical equation for expedite prediction of airflows emitted to the outside atmosphere (R2 = 0.77). Conversely, the same effect was not observed along the length of the sewer pipe, unlike the findings of other studies. The effect of a full flowing pipe at the downstream end of the gravity trunk sewer was also noticeable in downstream sewer pressurization and gas build-up. It was concluded that the magnitude of the gas pollutant emissions may heavily depend on the impacts of hydraulic flows and pumping characteristics in headspace pressure differences, denoting the need for better approaches when designing and installing venting stacks.

Improvements in Performance of a Self-Similarity Heat Sink Through Structure Modification

A self-similarity heat sink (SSHS) exhibits better overall performance than a conventional heat sink whereas although serious flow maldistribution still occurs. A modification to a conventional SSHS is proposed to overcome this disadvantage and obtain a more uniform heat transfer. Straight fins on the cover plate were replaced by zigzag fins to form a smaller incidence angle of fluid from the inlet manifold to the overflow channels, and the inlet manifold with constant cross-section was changed to a tapered inlet manifold to restrict excess flow to the downstream end of the inlet manifold. Numerical analysis was subsequently conducted to verify the modification. The results showed that the modification scheme successfully addressed the disadvantage of flow maldistribution of the original SSHS. Effects of the incidence angle on flow and heat transfer inside a single unit were analyzed at flow rates of 0.58–1.73 kg/h. The optimal incidence angle was found to be in the range of 20°–25°. For an entire SSHS with this optimal design, uniformity in flow distribution and heat transfer was significantly improved compared with original design, although the pressure drop increased slightly.

Towards understanding potential atmospheric contributions to abrupt climate changes: characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation

Abstract. Abrupt climate shifts of large amplitudes were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately 20 000 years ago, but their causes are not yet established. Midlatitude atmospheric dynamics may have played an important role in these climate variations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterizes deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations using the PlaSim Earth system model (run at T42 resolution) and the TraCE-21ka (T31) simulation. Though driven with yearly updates in surface elevation, we detect multiple instances of NAtl jet transitions in the PlaSim simulations that occur within 10 simulation years and a sensitivity of the jet to background climate conditions. Thus, we suggest that changes to the NAtl jet may play an important role in abrupt glacial climate changes. We identify two types of simulated wind changes over the last deglaciation. Firstly, the latitude of the NAtl eddy-driven jet shifts northward over the deglaciation in a sequence of distinct steps. Secondly, the variability in the NAtl jet gradually shifts from a Last Glacial Maximum (LGM) state with a strongly preferred jet latitude and a restricted latitudinal range to one with no single preferred latitude and a range that is at least 11∘ broader. These changes can significantly affect ocean circulation. Changes to the position of the NAtl jet alter the location of the wind forcing driving oceanic surface gyres and the limits of sea ice extent, whereas a shift to a more variable jet reduces the effectiveness of the wind forcing at driving surface ocean transports. The processes controlling these two types of changes differ on the upstream and downstream ends of the NAtl eddy-driven jet. On the upstream side over eastern North America, the elevated ice sheet margin acts as a barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability in the jet at LGM, so the jet shifts in sync with ice sheet margin changes. In contrast, the downstream side over the eastern NAtl is more sensitive to the thermal state of the background climate. Our results suggest that the presence of an elevated ice sheet margin in the south-eastern sector of the North American ice complex strongly constrains the deglacial position of the jet over eastern North America and the western North Atlantic as well as its variability.

Seasonal variations in heavy metals in water and sediment samples from River Tano in the Bono, Bono East, and Ahafo Regions, Ghana.

Seasonal variations in mercury (Hg), cadmium (Cd), zinc (Zn), lead (Pb), arsenic (As), copper (Cu), and chromium (Cr) metal concentrations in 36 water and 36 sediment samples from River Tano were studied using Perkin Elmer atomic absorption spectrophotometer (AAS) between November 2016 and October 2017. Significantly higher metal concentrations were recorded in rainy season than dry season for both water and sediment except for Pb and Cd where sediment concentrations were higher in the dry season. Cu was detected only in the sediment samples. Spatially the source of the river is unpolluted for all the metals in both seasons but the midstream and downstream ends of the river were heavily polluted by Hg, Pb, and Cd. All the heavy metals studied except Zn exceeded the WHO standards for drinking water. In the sediment, Cd, Hg, and Cr concentrations exceeded the USEPA guidelines. Igeo and Concentration Factor analysis revealed unpolluted sediments in terms of Cu, Pb, As, and Cr. They were near the background concentrations but Hg and Cd were in the range of moderate to heavy pollution. All the metals correlated significantly among themselves to signify common source to the water. It thus remains risky to use untreated water from the midstream and downstream of River Tano for domestic purposes. Enforcement of the buffer zone policy is recommended to avert further deterioration of the river water and sediment qualities.

Deformation analysis of suspended type cut off wall of diversion structures

Numerical study is carried out to analyse the behaviour of cut off walls in sandy soil, under constant differential pressure head, by varying its location from upstream end to downstream end. The deformation and bending moment in cut off wall are at their lowest magnitude when the cut off wall is positioned at upstream end. The cut off wall is subjected to second lowest deformation, when it is positioned at downstream end. The maximum deformation occurs, when the cut off wall is positioned at 0.60 times the total width of diversion dam from upstream end. The seepage rate in the diversion dam is highest when the cut off wall is positioned at centre of the diversion dam. The seepage rate in the diversion dam is having direct relation with the maximum displacement and maximum bending moment. The seepage force found to be more predominant than the pressure gradient and active pore pressure variations in deforming the cut off walls of diversion dams.

Probing In Vivo Structure of Individual mRNA 3' Isoforms Using Dimethyl Sulfate.

The DMS region extraction and deep sequencing (DREADS) procedure was designed to probe RNA structure in vivo and to link this structural information to specific 3' isoforms. Growing cells are treated with the alkylating agent dimethyl sulfate (DMS), which enters easily into cells and modifies RNA molecules at solvent-exposed A and C residues. RNA is isolated, and sequencing libraries are constructed in a manner that preserves the identities of individual mRNA isoforms arising from alternative cleavage/polyadenylation sites. During the cDNA synthesis step of library construction, the progress of reverse transcriptase (RT) is blocked when it encounters a DMS modification on the RNA, leading to disproportionate cDNA termination adjacent to DMS-modified positions. After paired-end deep sequencing, the downstream end of each sequenced fragment is mapped to a specific cleavage/poly(A) site representing an individual mRNA 3' isoform. The upstream mapped end of the sequenced fragment defines where the RT reaction stopped. Over the population of all sequenced fragments derived from a particular isoform, A and C positions that are overrepresented next to the upstream endpoints in the DMS sample (relative to a parallel untreated control) are inferred to have been DMS modified, and hence solvent exposed. This method thus allows in vivo structural information obtained using DMS to be linked to individual mRNA 3' isoforms. © 2019 by John Wiley & Sons, Inc.

Development of helical, fish-inspired cross-step filter for collecting harmful algae

A new filter was developed to collect harmful algae colonies by adapting the cross-step filtration structures and mechanisms discovered recently in filter-feeding fish. Extending beyond previously published models that closely emulated the basic morphology of the fish, the new cross-step filter’s major innovations are helical slots, radial symmetry, and rotation as an active anti-clogging mechanism. These innovations enable the transport of concentrated particles to the downstream end of the filter. This advance was made possible by recognizing that biologically imposed constraints such as bilateral symmetry do not apply to human-made filters. The use of helical slots was developed in a series of iterative tests that used water-tracing dye and algae-sized microspheres. The major products of the iterative tests were refinements in the helical design and an understanding of how varying the major structural parameters qualitatively influenced fluid flow and filter performance. Following the iterative tests, the clogging behavior of select filters was quantified at high particle concentrations. Vortices in the helical filter were effective at reducing clogging in the center of the slots. By considering the design space that is free of the biological constraints on the system and exploring the effects of variations in major structural parameters, our work has identified promising new directions for cross-step filtration and provided key insights into the biological system.

Local Scour at Complex Bridge Piers in Close Proximity under Clear-Water and Live-Bed Flow Regime

In this study, we investigated the characteristics of scour at complex bridge piers in close proximity. The experiments were performed under both clear-water and live-bed flow regimes. We compare our results with those for a single complex pier. Further, the performance of existing predictors is discussed. In this study, four typical pier arrangements were adopted, including side-by-side with aligned or 30° skewed flow, staggered, and tandem. The results show that the skew angle for a side-by-side arrangement significantly accelerates the clear-water scour development at all the vertical piles as well as between the piers, and the most scoured pile shifts from the upstream end to the downstream end of the upstream pier flank. The staggered and tandem pier arrangement show significant protection to the downstream pier for both the developing rate and the equilibrium scour depth. When the flow velocity exceeds the threshold for general bed motion, the clear-water scour pattern for all the pier arrangements may be altered significantly due to the upstream sediment supply, the weakened protection effect, and the enhanced flow contraction. The bed-forms migrate via the bridge opening and are damped gradually by the flow, and thus the response of the bed morphology under live-bed conditions is quite unsteady.

Applicability of Kinematic model for mud-flows: An unsteady analysis

The Kinematic Wave Model (KWM), representing a simplification of the Full Wave Model (FWM) under the shallow-water approximation, is often used in the one-dimensional formulation for describing the dynamics of debris/mud flood. The present work investigates the applicability conditions of the KWM to analyze mud floods, characterized by a rheological behaviour expressed through a power-law model. The study is carried out through the numerical solution of both the Full and Kinematic Wave models changing the characteristic time of hydrograph, i.e. the wave duration, imposed at the channel inlet. The predictions of the two models are compared in terms of maximum flow depth, maximum discharge and peak discharge at the downstream channel end. The study is performed for several values of the Froude (F) and the Kinematic Wave (K) numbers. Similarly to the clear-water case, present results show that higher errors in applying KWM pertain to shorter flood wave durations, but the performance of KWM appears to strongly depend on the value of the rheological index, becoming worse as the fluid rheology becomes more shear-thinning. The study furnishes applicability criteria representing a guideline for practical applications in terms of minimum wave duration above which the KWM error in reproducing the considered flood characteristics (the maximum flow depth, the maximum discharge and the peak discharge at the downstream channel end) is less or equal than 5%. Finally, it has been shown that the wave period criterion, obtained considering linearized wave dynamics, may be safely applied at least for fluid with moderate shear-thinning behavior and for moderate values of the dimensionless number KF2.

Improved SVR machine learning models for agricultural drought prediction at downstream of Langat River Basin, Malaysia

Abstract Drought is a harmful and little understood natural hazard. Effective drought prediction is vital for sustainable agricultural activities and water resources management. The support vector regression (SVR) model and two of its enhanced variants, namely, fuzzy-support vector regression (F-SVR) and boosted-support vector regression (BS-SVR) models, for predicting the standardized precipitation evapotranspiration indices (SPEI) (in this case, SPEI-1, SPEI-3 and SPEI-6, at various timescales) with a lead time of one month, were developed to minimize potential drought impact on oil palm plantations at the downstream end of the Langat River Basin, which has a tropical climate pattern. Observed SPEIs from periods 1976 to 2011 and 2012 to 2015 were used for model training and validation, respectively. By applying the MAE, RMSE, MBE and R2 as model assessments, it was found that the F-SVR model was best with the trend of improving accuracy when the timescale of the SPEIs increased. It was also found that differences in model performance deteriorates with increased timescale of the SPEIs. The outlier reducing effect from the fuzzy concept has better improvement for the SVR-based models compared to the boosting technique in predicting SPEI-1, SPEI-3 and SPEI-6 for a one-month lead time at the downstream of Langat River Basin.

Application of a Magnetic Mirror to Increase Total Efficiency in Relativistic Magnetrons

The relativistic magnetron is the most compact and efficient high-power microwave source. Inorder to further increase the total efficiency of microwave generation in a relativistic magnetron with diffraction output with a low-energy state of electrons that is formed between two virtual cathodes (VCs) in the interaction space, the second VC at the downstream end of the interaction space is replaced with a magnetic mirror that reflects all leakage electrons back into the interaction space. Previously these leakage electrons were deposited on the anode surface without interacting with the microwaves. Particle-in-cell simulations show that this configuration of relativistic magnetron increases the electronic efficiency from 86% to 92%, and increases the total efficiency up to the maximal electronic efficiency. This is a record high efficiency of microwave generation in a relativistic magnetron or any other gigawatt-class, gigahertz-frequency HPM source.

The effect of supplemental irrigation from polyacrylamide-treated microcatchments on the growth of acacia saligna in dryland

A field study was carried to determine the impact of the land application of polyacrylamide (PAM) on the runoff used for supplemental irrigation. Five treatments were investigated: PAM A-130, PAM A-836, PAM Aerotil, plastic mulch, and natural (no PAM no mulch). Runoff was collected in barrels placed at the downstream end of fifteen plots and then used for the irrigation of acacia trees planted in an experimental site in Jordan. The growth characteristics of the acacia were monitored over a two-year period from 2009 to 2010. The total runoff volumes were significantly different over PAM A-836, PAM Aerotil, and plastic mulch compared to the natural. The results showed that supplemental irrigation of acacia with water collected from PAM plots significantly increased the acacia height and number of leaves compared to the natural and rainfed treatments. The use of PAM-treated runoff also slightly increased the number of branches of the acacia, but the increase was only significant in the case of PAM A-836. There was a weak correlation between the volume of supplemental irrigation generated and the morphological characteristics. The type of PAM seems to have improved plant growth irrespective of the volume of runoff collected.