Comparing the runoff decompositions of small testbed catchments: end-member mixing analysis against hydrological modelling

This study is focused on the comparison of catchment streamflow composition simulated with three well-known rainfall-runoff (RR) models (ECOMAG, HBV, SWAT) against hydrograph decomposition onto the principal constituents evaluated from End-Member Mixing Analysis (EMMA). There used the data provided by the short-term in-situ observations at two small mountain-taiga experimental catchments located in the south of Pacific Russia. All used RR models demonstrate that two neighboring small catchments disagree significantly in mutual dynamics of the runoff fractions due to geological and landscape structure differences. The geochemical analysis confirmed the differences in runoff generation processes at both studied catchments. The assessment of proximity of the runoff constituents to the hydrograph decomposition with the EMMA that makes a basis for the RR models benchmark analysis. We applied three data aggregation intervals (season, month and pentad) to find a reasonable data generalization period ensuring results clarity. In terms of runoff composition, the most conformable RR model to EMMA is found to be ECOMAG, HBV gets close to reflect specific runoff events well enough, SWAT gives distinctive behavior against other models. The study shows that along with using the standard efficiency criteria reflected proximity of simulated and modelling values of runoff, compliance with the EMMA results might give useful auxiliary information for hydrological modelling results validation.

Improving the understanding of N transport in rural catchments under Atlantic climate conditions from analysis of the concentration-discharge relationship derived from a high frequency data set

Understanding processes controlling stream nutrient dynamics over time is crucial for implementing effective management strategies to prevent water quality degradation. In this respect, the study of the nutrient concentration-discharge (C-Q) relationship during individual runoff events can be a valuable tool for extrapolating the hydrochemical processes controlling nutrient fluxes from streams. This study investigated nitrogen concentration dynamics during events by analyzing and interpreting the nitrogen C-Q relationship in a small Atlantic (NW Iberian Peninsula) rural catchment. To this end, nitrate (NO3) and total Kjeldahl nitrogen (TKN) concentrations were monitored at high temporal resolution during 102 runoff events over a 6-year period. For each of the selected runoff events, C-Q response was examined visually for the presence and direction of hysteresis loops and classified into three types of responses: clockwise and anticlockwise and no hysteresis. Some metrics, such as the change in concentration (ΔC) and the overall dynamics of hysteresis loops (ΔR), were used to quantify nitrogen behavior during the runoff events. The results showed how transport mechanisms varied between parameters. The most frequent hysteretic response for NO3 was enrichment with anticlockwise rotation, indicating that subsurface flow is the main pathway to the stream. On the contrary, the TKN dynamic was dominated by clockwise hysteresis, suggesting that surface runoff is mainly responsible for the transport of TKN to the river. Hysteresis direction (ΔR) and magnitude (ΔC) were better explained by event characteristics, such as rainfall, runoff, and discharge increase than by antecedent conditions (antecedent precipitation and baseflow).

Ecohydrologie urbaine et changement climatique

Due to global change, cities of the future will have to deal with more intense runoff and longer drought sequences, in addition to a growing urban and peri-urban population. French Mediterranean cities, such as Toulon, are already densely urbanised and exposed to the effects of global warming. The adaptation of their infrastructures is problematic. Cities with high development potential, such as Dakar, offer the opportunity to imagine other solutions for the management of water resources and its extremes in the context of global change. In particular, it is a question of managing the flows of water and substances linked to intense runoff events according to an ecohydrological logic that makes it possible to reduce environmental risks and increase social and economic benefits. To do this, we use a hydrologically-based geomatics model (IRIP) that produces predictive maps of areas of generation, transfer and accumulation of intense runoff and associated nutrients. This allows us to target effective intervention areas to reduce risks and increase water resources, for example by simulating land use change in appropriate locations and at the same time stimulating specific biological processes. The fundamental principle of ecohydrology is to balance energy flows with biological metabolic flows at the sub-catchment scale. The mapping of intense runoff processes is a first step illustrated in this article for the cities of Toulon and Dakar. This first step is part of the Dakar'2030 project, which aims to rethink urban development and adapt it to climate change.

Copper, Zinc and Iron Contamination in Wellington Streams After Rainfall Events

<p>This work set out to determine the concentrations of dissolved copper (Cu), zinc (Zn) and iron (Fe) during base and wet weather flow at streams throughout the Wellington region. The secondary objective was to investigate possible sources of heavy metals during rainfall events. The concentrations of the three dissolved trace metals Cu, Zn and Fe were measured at 13 sites on five streams during base flow conditions and during runoff events (wet weather flow) in the Wellington region between January and July 2011. More than 240 base flow and 100 wet weather flow samples have been analysed for the three dissolved metals. Additionally, rainfall, roof runoff and paved surface runoff samples have been collected and analysed. The analysis was performed by Flame Atomic Absorption Spectroscopy (FAAS). A pre-concentration procedure using Chelex-100, a chelating polymeric resin bead, was developed and successfully used to enhance the concentrations of dissolved Cu and dissolved Zn. The recorded data were compared to the recommended long-term (chronic) toxicity triggers; the Australian and New Zealand Environment and Conservation Council freshwater toxicity trigger values (ANZECC (2000) TV) for dissolved Cu and Zn, and the Canadian trigger value (CTV) for dissolved Fe. Additionally, the concentrations of dissolved Cu and Zn in storm water samples were compared against the recommended short-term (acute) toxicity triggers, the United States Environmental Protection Agency (USEPA 2006) Criteria Maximum Concentrations (CMC). The medians of dissolved heavy metals concentrations; Cu, Zn, and Fe, all of which are potentially toxic to aquatic life, exceeded the long-term (chronic) toxicity guidelines at one of the studied sites for Fe, nine sites (69%) for Cu and 10 sites (77%) for Zn in base flow conditions. Comparison of base flow monitoring data to previous reports showed that the concentrations of the studied metals have increased over the last five years. Storm water (wet weather flow conditions) contained elevated levels of dissolved heavy metals in comparison to base flow concentrations which is consistent with what has been reported previously. Dissolved Cu and Zn exceeded the acute toxicity criteria at sites of suburban residential areas. The median of dissolved Fe concentration exceeded the sustained toxicity exposure trigger at eight of the studied sites (61%). Distinct catchment type contaminant concentrations (dissolved Cu and Zn) were observed during storm runoff events with a concentration pattern of suburban residential > commercial > light residential > rural catchment. Dissolved Fe exhibited a similar pattern but in this case the concentration in rural catchments was higher than in light residential catchments. These observations were attributed to the high traffic of vehicles passing nearby the area; accumulated particulate materials; and corrosion of materials containing heavy metals, such as galvanised and copper roofs, gutter systems and building construction materials. The strongest and most obvious first flush effect was observed with dissolved Cu followed by Zn where the phenomenon was observed in six storm runoff events for Cu and five events for Zn. The first flush effect of dissolved Fe was present in three out of eight storm runoff events. The concentrations of dissolved metals were of the same order of magnitude as those previously reported for the Wellington region, but this work recorded the highest expected concentrations, particularly, for dissolved Fe. The reported data are consistent with data sets from other New Zealand regions. The investigation of possible sources of dissolved heavy metals in storm runoff samples showed that rainfall water contained markedly elevated concentrations of dissolved Zn and smaller Cu concentrations, 0.04-0.075 and 0.0018-0.01 mg/L respectively, in comparison to the ANZECC (2000) TVs, 0.008 and 0.0014 mg/L respectively. The concentrations of dissolved Fe were below the CTV level of 0.3 mg/L. Most studies conducted in New Zealand did not take into account the atmospheric precipitation contribution to the elevated concentrations of dissolved metals during runoff events. Roof runoff samples had similar dissolved Cu and Fe concentration to those recorded in atmospheric rainfall water, but Zn was found to be higher in galvanised roof runoff. First flush samples from roof runoff had higher concentrations of all three metals than the delayed runoff samples, indicating the presence of accumulated particles containing metals. Paved surface runoff samples had concentrations of dissolved Cu and Zn higher than the chronic toxicity triggers, but the medians did not exceed the acute toxicity guidelines. The value of the median for the concentrations of dissolved Fe was below the CTV criteria. Similar results have been published for surface runoff in New Zealand and the international literature related to this field.</p>

Copper, Zinc and Iron Contamination in Wellington Streams After Rainfall Events

<p>This work set out to determine the concentrations of dissolved copper (Cu), zinc (Zn) and iron (Fe) during base and wet weather flow at streams throughout the Wellington region. The secondary objective was to investigate possible sources of heavy metals during rainfall events. The concentrations of the three dissolved trace metals Cu, Zn and Fe were measured at 13 sites on five streams during base flow conditions and during runoff events (wet weather flow) in the Wellington region between January and July 2011. More than 240 base flow and 100 wet weather flow samples have been analysed for the three dissolved metals. Additionally, rainfall, roof runoff and paved surface runoff samples have been collected and analysed. The analysis was performed by Flame Atomic Absorption Spectroscopy (FAAS). A pre-concentration procedure using Chelex-100, a chelating polymeric resin bead, was developed and successfully used to enhance the concentrations of dissolved Cu and dissolved Zn. The recorded data were compared to the recommended long-term (chronic) toxicity triggers; the Australian and New Zealand Environment and Conservation Council freshwater toxicity trigger values (ANZECC (2000) TV) for dissolved Cu and Zn, and the Canadian trigger value (CTV) for dissolved Fe. Additionally, the concentrations of dissolved Cu and Zn in storm water samples were compared against the recommended short-term (acute) toxicity triggers, the United States Environmental Protection Agency (USEPA 2006) Criteria Maximum Concentrations (CMC). The medians of dissolved heavy metals concentrations; Cu, Zn, and Fe, all of which are potentially toxic to aquatic life, exceeded the long-term (chronic) toxicity guidelines at one of the studied sites for Fe, nine sites (69%) for Cu and 10 sites (77%) for Zn in base flow conditions. Comparison of base flow monitoring data to previous reports showed that the concentrations of the studied metals have increased over the last five years. Storm water (wet weather flow conditions) contained elevated levels of dissolved heavy metals in comparison to base flow concentrations which is consistent with what has been reported previously. Dissolved Cu and Zn exceeded the acute toxicity criteria at sites of suburban residential areas. The median of dissolved Fe concentration exceeded the sustained toxicity exposure trigger at eight of the studied sites (61%). Distinct catchment type contaminant concentrations (dissolved Cu and Zn) were observed during storm runoff events with a concentration pattern of suburban residential > commercial > light residential > rural catchment. Dissolved Fe exhibited a similar pattern but in this case the concentration in rural catchments was higher than in light residential catchments. These observations were attributed to the high traffic of vehicles passing nearby the area; accumulated particulate materials; and corrosion of materials containing heavy metals, such as galvanised and copper roofs, gutter systems and building construction materials. The strongest and most obvious first flush effect was observed with dissolved Cu followed by Zn where the phenomenon was observed in six storm runoff events for Cu and five events for Zn. The first flush effect of dissolved Fe was present in three out of eight storm runoff events. The concentrations of dissolved metals were of the same order of magnitude as those previously reported for the Wellington region, but this work recorded the highest expected concentrations, particularly, for dissolved Fe. The reported data are consistent with data sets from other New Zealand regions. The investigation of possible sources of dissolved heavy metals in storm runoff samples showed that rainfall water contained markedly elevated concentrations of dissolved Zn and smaller Cu concentrations, 0.04-0.075 and 0.0018-0.01 mg/L respectively, in comparison to the ANZECC (2000) TVs, 0.008 and 0.0014 mg/L respectively. The concentrations of dissolved Fe were below the CTV level of 0.3 mg/L. Most studies conducted in New Zealand did not take into account the atmospheric precipitation contribution to the elevated concentrations of dissolved metals during runoff events. Roof runoff samples had similar dissolved Cu and Fe concentration to those recorded in atmospheric rainfall water, but Zn was found to be higher in galvanised roof runoff. First flush samples from roof runoff had higher concentrations of all three metals than the delayed runoff samples, indicating the presence of accumulated particles containing metals. Paved surface runoff samples had concentrations of dissolved Cu and Zn higher than the chronic toxicity triggers, but the medians did not exceed the acute toxicity guidelines. The value of the median for the concentrations of dissolved Fe was below the CTV criteria. Similar results have been published for surface runoff in New Zealand and the international literature related to this field.</p>

Applying a Graphical Method in Evaluation of Empirical Methods for Estimating Time of Concentration in an Arid Region

At gauged watersheds, the time of concentration can be estimated using rainfall-runoff data; however, at ungauged watersheds, empirical methods are used instead. Large errors in the application of empirical methods may cause inaccurate modeling of floods and unreliable structure design. In this paper, methods for calculating the time of concentration (Tc) were compared to identify the best equation for estimating Tc in ungauged watersheds of an arid region. The graphical method, based on measured data, was compared to 15 empirical methods to determine which empirical method returned the best results. The graphical method was applied to 33 rainfall-runoff events in four rural sub-watersheds located in the central parts of Hormozgan province, Iran. A ranking-based procedure was used to select the best performing empirical methods. To minimize bias and improve accuracy, the best performing empirical methods were modified by adjusting their formulas. According to the study, three empirical methods: (1) Williams, (2) Pilgrim and Mac Dermott, and (3) Arizona DOT, performed the best in the study areas. The results also showed that the modified Williams and Arizona DOT’s formulas were able to estimate the time of concentration in ungauged watersheds with an error lower than 1%.

F-Specific RNA Bacteriophage Transport in Stream Water: Hydro-Meteorological Controls and Association with Suspended Solids

F-specific RNA bacteriophages (FRNAPHs) are commonly used as indicators of faecal and viral contamination in waters. Once they enter surface waters, the exact role of suspended solids, sediments and hydro-meteorological factors in their fluvial fate and transport is poorly understood, and long-term studies (e.g., over years) are lacking. In this study, FRNAPH concentrations and genogroup distribution were measured in the Orne River (France) during two years at weekly intervals, and during four storm runoff events. Hydro-meteorological driving factors were investigated at both time scales. FRNAPH concentrations and genogroups at different depths of a riverbank sediment core were also examined to better discriminate the origin of the faecal pollution. During low flows, the FRNAPH and the suspended solid transport were decoupled and the FRNAPH concentrations were mainly correlated with the air and water temperature. During storm runoff events, the FRNAPH concentrations only showed a significant correlation with conductivity, turbidity and water discharge. Despite the uncertainty of the predictions, multi parameter regression models using hydro-meteorological variables were suitable to predict log transformed FRNAPHs’ concentrations at low flows with a standard error of 0.46. Model performance using the storm runoff events dataset was low. This study highlights different driving factors at low flows and during storm runoff events, and the need to measure at both time scales to better understand phage transport dynamics in surface water.