Watershed Outflow Research Articles

Faecal contamination determines bacterial assemblages over natural environmental parameters within intermittently opened and closed lagoons (ICOLLs) during high rainfall

Intermittently closed and opened lakes and lagoons (ICOLLs) provide important ecosystem services, including food provision and nutrient cycling. These ecosystems generally experience low watershed outflow, resulting in substantial fluctuations in physicochemical parameters that are often compounded by anthropogenic contamination, however the patterns in microbiology within these environments remains uncharacterised. Therefore, we aimed to determine how seasonal heterogeneity in the physicochemical parameters, in comparison to faecal contamination, alter the dynamics of bacterial communities inhabiting ICOLLs on the eastern Australian coast. To address these aims, we sampled four ICOLLs on a monthly basis for one year, using 16S rRNA gene amplicon sequencing to monitor patterns in bacterial diversity and qPCR-based methods to measure faecal contamination from humans (sewage), dogs, and birds. Additionally, we used qPCR to monitor patterns of a suite of antibiotic resistance genes (ARGs) including sulI, tetA, qnrS, dfrA1, and vanB. Differences in bacterial community composition were often associated with temporal shifts in salinity, temperature, pH, DO, and fDOM, but following periods of high rainfall, bacterial assemblages in two of four ICOLLs changed in direct response to sewage inputs. Within these ICOLLs, indicator taxa for stormwater identified using the 16S rRNA amplicon sequencing data, as well as markers for sewage and dog faeces, and levels of the antibiotic resistance genes (ARGs) sulI, tetA, and dfrA1 were significantly more abundant after rainfall. Notably many of the stormwater indicator taxa were potential human pathogens including Arcobacter and Aeromonas hydrophilia, which also displayed significant correlations, albeit weak to moderate, with levels of the ARGs sulI, tetA, and dfrA1. This broad-scale shift in the nature of the bacterial community following rainfall will likely lead to a substantial, and perhaps detrimental, divergence in the ecosystem services provided by the bacterial assemblages within these ICOLLs. We conclude that following rainfall events, sewage was a principal driver of shifts in the microbiology of ICOLLs exposed to stormwater, while natural seasonal shifts in the physicochemical parameters controlled bacterial communities at other times. Increased occurrence of intense precipitation events is predicted as a ramification of climate change, which will lead to increased impacts of stormwater and sewage contamination on important ICOLL ecosystems in the future.

Coupling Reservoir Operation and Rainfall‐Runoff Processes for Streamflow Simulation in Watersheds

AbstractWe assess the overall watershed system representation via fully coupling a generic reservoir operation model with a conceptual rainfall‐runoff model. The performance of the coupled model is evaluated comprehensively by examining watershed outflow simulations, model parameter values, and a key internal flux of the watershed model (here reservoir inflow). Five published generic reservoir operation models are coupled with a watershed rainfall‐runoff model, and results are compared across the coupled models and one additional model called ResIgnore that ignores reservoir operation. Traditional loosely coupled watershed hydrologic models (where calibrated inflow is routed through reservoir operation models) are used as baselines to examine the differences in simulation performance and parameterization obtained from the fully coupled models. We find that fully coupling the Generic Data‐Driven Reservoir Operation Model (GDROM) and the Dynamically Zoned Target Release (DZTR) reservoir operation models with the rainfall‐runoff model obtains robust simulations of watershed outflow with realistic parameterization, suggesting that they can be reliably integrated into large‐scale hydrological models for simulating streamflow in heavily dammed watersheds. Our results also show that compared to ResIgnore, the fully coupled watershed models more accurately simulate the entire distribution of watershed outflow, obtain more realistic values of model parameters, and simulate reservoir inflow with higher accuracy. Finally, we note that the prediction intervals of watershed outflow obtained from the GDROM‐ and DZTR‐based fully coupled models consistently envelop observed watershed outflow across the study watersheds, indicating that GDROM and DZTR can be suitable reservoir components of large‐scale hydrology models.

A streamflow hydrograph analysis and simulation for a study case watershed

The streamflow hydrograph analysis and simulation for a study case watershed was carried out using the hydrologic engineering centre - geospatial hydrologic modelling system (HEC-GeoHMS) and the hydrologic engineering centre - hydrologic modelling system (HEC-HMS) software coupling. HEC-GeoHMS is integrated in a geographic information system (GIS) so as to develop a terrain's pre-processing tool and to generate output files which are inputted to the hydrologic model. Soil map data, land use map and digital elevation model (DEM) were used in order to delineate the physical watershed's characteristics. The runoff estimation was based on the soil conservation service curve number (SCS-CN) approach while the watershed's outflow estimation was carried out by employing SCS unit hydrograph method. The rainfall - runoff modelling is applied on a storm event which occurred on 01/10/2005 at Kastaneri watershed. The coupled hydrological models simulated runoff hydrograph for the latter storm event whilst the CN and the peak discharge values were computed equal to 69.5 and 72.8 m3/s respectively.

Multi-station streamflow forecasting using wavelet denoising and artificial intelligence models

In this research, the hybrid of threshold based wavelet denoising with Extreme Learning Machine (ELM) and Least Square Support Vector Machine (LSSVM) models would be investigated in order to forecast Snoqualmie watershed daily Multi-Station (MS) streamflow. For this purpose, firstly, the watershed outflow was forecasted using models of ELM and LSSVM only with one station individually without any pre-processing. So, MS-ELM and MS-LSSVM were applied for using all sub-basins data synchronously. Ultimately, the sub-basins streamflow were denoised using wavelet based thresholding approach, and next, in a MS framework, the purified signals were imposed into the ELM and LSSVM models. It was obtained the ELM preference compared to the LSSVM, and MS model with compared to the individual sub-basin model, considering denoised data with respect to the noisy data, for example, DCLSSVM=0.82, DCELM=0.84, DCMS-ELM=0.90, DCdenoised-MS-ELM=0.93.

Can urban pluvial flooding be predicted by open spatial data and weather data?

Cities are increasingly prone to urban flooding due to heavier rainfall, denser populations, augmenting imperviousness, and infrastructure aging. Urban pluvial flooding causes damage to buildings and contents, and disturbs stormwater drainage, transportation, and electricity provision. Designing and implementing efficient adaptation measures requires proper understanding of the urban response to heavy rainfall. However, implemented stormwater drainage models lack flood impact data for calibration, which results in poor flood predictions. Moreover, such models only consider rainfall and hydraulic parameters, neglecting the role of other natural, built, and social conditions in flooding mechanisms. This paper explores the potential of open spatial datasets to explain the occurrence of citizen-reported flood incidents during a heavy rain event. After a dimensionality reduction, imperviousness and proximity to watershed outflow point were found to significantly explain up to half of the flooding incidents variability, proving the usefulness of the proposed approach for urban flood modelling and management.

Proton production from nitrogen transformation drives stream export of base cations in acid-sensitive forested watersheds

The biogeochemical cycles of nitrogen (N) and base cations (BCs), (i.e., K+, Na+, Ca2+, and Mg2+), play critical roles in plant nutrition and ecosystem function. Empirical correlations between large experimental N fertilizer additions to forest ecosystems and increased BCs loss in stream water are well demonstrated, but the mechanisms driving this coupling remain poorly understood. We hypothesized that protons generated through N transformation (PPRN)—quantified as the balance of NH4+ (H+ source) and NO3− (H+ sink) in precipitation versus the stream output will impact BCs loss in acid-sensitive ecosystems. To test this hypothesis, we monitored precipitation input and stream export of inorganic N and BCs for three years in an acid-sensitive forested watershed in a granite area of subtropical China. We found the precipitation input of inorganic N (17.71kgNha−1year−1 with 54% as NH4+–N) was considerably higher than stream exported inorganic N (5.99kgNha−1year−1 with 83% as NO3−–N), making the watershed a net N sink. The stream export of BCs (151, 1518, 851, and 252molha−1year−1 for K+, Na+, Ca2+, and Mg2+, respectively) was positively correlated (r=0.80, 0.90, 0.84, and 0.84 for K+, Na+, Ca2+, and Mg2+ on a monthly scale, respectively, P<0.001, n=36) with PPRN (389molha−1year−1) over the three years, suggesting that PPRN drives loss of BCs in the acid-sensitive ecosystem. A global meta-analysis of 15 watershed studies from non-calcareous ecosystems further supports this hypothesis by showing a similarly strong correlation between ∑BCs output and PPRN (r=0.89, P<0.001, n=15), in spite of the pronounced differences in environmental settings. Collectively, our results suggest that N transformations rather than anions (NO3− and/or SO42−) leaching specifically, are an important mediator of BCs loss in acid-senstive ecosystems. Our study provides the first definitive evidence that the chronic N deposition and subsequent transformation within the watershed drive stream export of BCs through proton production in acid-sensitive ecosystems, irrespective of their current relatively high N retention. Our findings suggest the N-transformation-based proton production can be used as an indicator of watershed outflow quality in the acid-sensitive ecosystems.

Applying the Soil Water Assessment Tool to 5th Canadian Division Support Base Gagetown

A hydrologic and water quality model is sought to establish an approach to land management decisions for a Canadian Army training base. Training areas are subjected to high levels of persistent activity creating unique land cover and land-use disturbances. Deforestation, complex road networks, off-road manoeuvres, and vehicle stream crossings are among major anthropogenic activities observed to affect these landscapes. Expanding, preserving and improving the quality of these areas to host training activities for future generations is critical to maintain operational effectiveness. Inclusive to this objective is minimizing resultant environmental degradation, principally in the form of hydrologic fluctuations, excess erosion, and sedimentation of aquatic environments. Application of the Soil Water Assessment Tool (SWAT) was assessed for its ability to simulate hydrologic and water quality conditions observed in military landscapes at 5th Canadian Division Support Base (5 CDSB) Gagetown, New Brunswick. Despite some limitations, this model adequately simulated three partial years of daily watershed outflow (NSE = 0.47–0.79, R2 = 0.50–0.88) and adequately predicted suspended sediment yields during the observation periods (%d = 6–47%) for one highly disturbed sub-watershed in Gagetown. Further development of this model may help guide decisions to develop or decommission training areas, guide land management practices and prioritize select landscape mitigation efforts.

Mapping of critical source areas for diffuse fecal bacterial pollution in extensively grazed watersheds

Microbial contamination of surface waters frequently occurs on permanent natural grasslands subject to extensive grazing. Management of these problems requires developing methods to identify critical source areas that are responsible of significant losses of fecal microorganisms. In this study, GIS analysis of watersheds was used to calculate the flow of fecal bacteria ( Escherichia coli) to the outflow of a watershed by summing bacterial flows in runoff from pixels containing cowpats. Calculations were performed in two steps: (i) identification of pixels with bacteria and runoff by modeling the distribution of cowpats and variable sources of surface runoff, and (ii) parameterization by inverse analysis of deterministic and stochastic functions for bacterial emission from cowpats and for retention during their transmission to the watershed outflow. During bacterial transport in water flow, bacterial retention on the soil surface has a large influence. Despite this effect, bacterial concentration in runoff remains high. In general, cowpat age, runoff volumes and the location and proportions of bacteria-emitting and non-emitting surfaces determine critical source areas and bacterial flows at the watershed outflow. These data are discussed in terms of feasibility of solutions for management of watercourses and grazing practices.

A Dissipative Hydrological Model for the Hotan Oasis (DHMHO)

Various hydrological models have been designed to simulate moisture transformation in the water-cycle system between atmospheric water, surface water, soil water and groundwater. But few have been designed specially for oases in arid desert areas where the ecology and the environment are vulnerable because of unwise water-land resources utilization. In order to analyze the moisture transformation in the Hotan Oasis in the Taklimakan Desert in China, and hence to provide scientific references for the rational exploitation and allocation of the limited water-land resources, for the purpose of ensuring that the vulnerable ecology and environment there can be gradually improved and the social economy there can develop sustainably, a dissipative hydrological model for the Hotan Oasis (DHMHO) was developed. It was an outcome of years of systematic study on the moisture transformation in arid areas and on the water–land conditions in the Hotan Oasis. Based on statistics, DHMHO introduces two empirical equations whereby we dynamically calibrated model parameters with monthly data from year 1971 to 1995. Then the calibrated parameters were used to model the moisture movement from 1996 to 2003 and thereafter rationality check and error analysis were conducted. The error analysis results show that the absolute relative errors between simulated and observed groundwater depth values are almost (11 of 12 points) within 20%, and those in annual watershed outflow simulation are mostly (six of eight points) within 20% with an average annual Nash–Sutcliffe Efficiency Coefficient (NSEC) of 0.80. With DHMHO and IPCC assessment, we also simulated the moisture transformation and dissipation in the Hotan Oasis from the year 2011 to 2020. Results show details of the water resources in the Hotan Oasis in the next decade and hence are expected to provide scientific references for establishing rational exploitation and allocation policies on the local water–land resources in the future.

Evaluation of spring flow in the uplands of Matalom, Leyte, Philippines

In order to assess the reliability of the springs near Matalom, Leyte, Philippines as a sustainable source of drinking water, we measured precipitation and outflow of five small and two large springs for the region for a period of a year and analyzed the recession spring flow data. Although monthly spring flow follows a similar pattern to that of the rainfall, the regression relationship between both parameters is poor except for the smallest spring. To determine the dry season spring flow behavior, we analyzed the spring flow data with a mechanistic recession flow model originally developed for prediction of stream drought flow in the northeastern U.S. by Brutsaert and Nieber in 1977. The model describes the dry season spring flow well assuming that the aquifer behaves as a linear reservoir. The analysis shows that the flow “half-life” for the springs is about one month. By adding the individual spring flows to derive a watershed outflow we were able to evaluate how well the simple watershed geometry underlying the analysis of Brutsaert and Nieber [Regionalized drought flow hydrographs from a mature glaciated plateau. Water Resour Res 1977;13(3):637–43] applies to the more complex watersheds.

Phosphorus export from an agricultural watershed: linking source and transport mechanisms.

Many source and transport factors control P loss from agricultural landscapes; however, little information is available on how these factors are linked at a watershed scale. Thus, we investigated mechanisms controlling P release from soil and stream sediments in relation to storm and baseflow P concentrations at four flumes and in the channel of an agricultural watershed. Baseflow dissolved reactive phosphorus (DRP) concentrations were greater at the watershed outflow (Flume 1; 0.042 mg L(-1)) than uppermost flume (Flume 4; 0.028 mg L(-1)). Conversely, DRP concentrations were greater at Flume 4 (0.304 mg L(-1)) than Flume 1 (0.128 mg L(-1)) during stormflow. Similar trends in total phosphorus (TP) concentration were also observed. During stormflow, stream P concentrations are controlled by overland flow-generated erosion from areas of the watershed coincident with high soil P. In-channel decreases in P concentration during stormflow were attributed to sediment deposition, resorption of P, and dilution. The increase in baseflow P concentrations downstream was controlled by channel sediments. Phosphorus sorption maximum of Flume 4 sediment (532 mg kg(-1)) was greater than at the outlet Flume 1 (227 mg kg(-1)). Indeed, the decrease in P desorption between Flumes 1 and 4 sediment (0.046 to 0.025 mg L(-1)) was similar to the difference in baseflow DRP between Flumes 1 and 4 (0.042 to 0.028 mg L(-1)). This study shows that erosion, soil P concentration, and channel sediment P sorption properties influence streamflow DRP and TP. A better understanding of the spatial and temporal distribution of these processes and their connectivity over the landscape will aid targeting remedial practices.

Ecosystem processes at the watershed scale: Sensitivity to potential climate change

A distributed data and simulation system for forested watersheds was used to investigate the potential changes in watershed hydrological and ecological processes under hypothesized climate change scenarios. RHESSys (Regional HydroEcological Simulation System) incorporates a spatial representation of nested catchment and lake systems in a GIS, along with a set of process submodels to compute local flux and storage of energy, water, carbon, and nutrients. A hierarchy of potential climate change shifts in weather, forest canopy physiological processes, and forest cover were used to operate RHESSys for comparison with control simulations for present‐day conditions. Use of projected temperature and precipitation changes alone led to qualitatively different forecasts of watershed climate change impact when compared to simulations that also incorporated adjustment of canopy physiology to elevated concentrations of atmospheric CO2. In addition, ecosystem processes may be more resilient to climate change due to the existence of a series of offsetting effects. Annual net effects on specific processes such as watershed outflow and forest productivity may qualitatively vary from year to year rather than showing consistent increases or decreases relative to current conditions. The model results illustrate the significance of incorporating a reasonable description of terrestrial ecosystem processes within the contributing watershed when assessing the impact of climate change.

A Coupled, Field Hydrology – Open Channel Flow Model: Theory

A coupled, field hydrology and stream routing model is presented. It simulates field hydrology and routes field outflow through a canal network. Water levels in the canal can suppress field drainage. Backwater conditions and flooding in the stream are simulated. Sensitivity analysis for runoff events with one-half- to two-year return periods found watershed outflow to be sensitive to (in order of importance) time of concentration in the fields, bottom slope of the main channel, hydraulic conductivity of the soil, subsurface drain spacing in the field, and channel roughness. The simulated outflow was only moderately dependent on surface storage and was not dependent on channel depth and width, rooting depths or drainable porosity. The model can make multiple year simulations and can be used to analyze hydrologic effects of water management systems, changes in land use practices, tidal effects, and channel constrictions such as weirs or partial ditch blockage.

Convergence Criteria for Iterative Hydrologic Routing Models

An iterative process that is used to solve flow dynamics is studied; a highway culvert and embankment system serves as an example. Time step criteria governing convergence of the iterative process is analyzed. The Lipschitz ratio is applied to calculate the controlling algebraic time step relationship. The time step for convergence is shown to vary with current inflow and antecedent storage. Parameters of the iterative process are calculated for the example by assuming nonlinear functional forms for stage storage and discharge storage relationships and by inferring the appropriate coefficients. Numerical results are presented for several extreme cases that bracket orifice and weir flow conditions. The approach should be applicable to other hydrologic systems such as small dams, catch basin flow, and retarding basins. As for the route or convolute question, which concerns the direct conversion of rainfall excess to watershed outflow, this analysis aids in the selection of a time increment for direct routing.