Nearby Catchments Research Articles

Susceptibility modeling of hydro-morphological processes considered river topology

ABSTRACT Hydro-Morphological Processes (HMP, any natural phenomenon contained within the spectrum defined between debris flows and flash floods) are most likely to occur in small catchments, especially buffer zones along or near rivers. Rivers transfer matter and energy between hydrographic units, thus potentially affecting the occurrence of HMPs in nearby catchments. To date, previous HMP susceptibility studies based on data-driven modeling lacked taking into account these interactions between catchments. In this work, we fully considered the role played by river topology and developed a Topology-based HMP susceptibility model (Topo-HMPSM) to emulate the interactions between catchments and predict the susceptibility of HMPs for the Yangtze River Basin during 1985–2015. Results confirmed that our proposed model outperforms four selected baseline models with the best F1-score (mean = 0.744, best = 0.756) and relatively lower uncertainties. A graph-based deep neural network improves the predictive and interpretability of HMP susceptibility modeling using embedding learning techniques. This work attempts to set a standard for incorporating river topology into deep learning models. Our findings highlight the importance of river topology in predicting HMP and support better informed hazard mitigation strategies.

Carbon and nutrient pools and fluxes in unmanaged mountain Norway spruce forests, and losses after natural tree dieback

Forest areas infected by insects are increasing in Europe and North America due to accelerating climate change. A 2000–2020 mass budget study on major elements (C, N, P, Ca, Mg, K) in the atmosphere-plant-soil-water systems of two unmanaged catchments enabled us to evaluate changes in pools and fluxes related to tree dieback and long-term accumulation/losses during the post-glacial period. A bark-beetle outbreak killed >75 % of all trees in a mature mountain spruce forest in one catchment and all dead biomass was left on site. A similar forest in a nearby catchment was only marginally affected. We observed that: (1) the long-term (millennial) C and N accumulation in soils averaged 10–22 and 0.5–1.1 kg ha−1 yr−1, respectively, while losses of Ca, Mg, and K from soils ranged from 0.1 to 2.6 kg ha−1 yr−1. (2) Only <0.8 % and <1.5 % of the respective total C and N fluxes entering the soil annually from vegetation were permanently stored in soils. (3) The post-disturbance decomposition of dead tree biomass reduced vegetation element pools from 27 % (C) to 73 % (P) between 2004 and 2019. (4) Tree dieback decreased net atmospheric element inputs to the impacted catchment, and increased the leaching of all elements and gaseous losses of C (∼2.3 t ha−1 yr−1) and N (∼14 kg ha−1 yr−1). The disturbed catchment became a net C source, but ∼50 % of the N released from dead biomass accumulated in soils. (5) Despite the severe forest disturbance, the dissolved losses of Ca and Mg represented 52–58 % of their leaching from intact stands during the peaking atmospheric acidification from 1970 to 1990. (6) Disturbance-related net leaching of P, Ca, Mg, and K were 4, 69, 16, and 114 kg ha−1, respectively, which represented 7–38 % of the losses potentially related to sanitary logging and subsequent removal of the aboveground tree biomass.

Retention and loss pathways of soluble nutrients in biochar-treated slope land soil based on a rainfall simulator

Global food crisis makes intense agricultural activity necessary, which accelerates soil degradation and increases pollution risk to nearby catchments. Application of biochar can effectively retain plant-required nutrients in soils. However, the linkage between retention and loss pathways of nutrients is still unclear, particularly at slope lands. Therefore, a simulated rainfall experiment (rainfall intensity ​= ​50 ​mm ​h−1) was conducted in a sandy soil with 10° gradient slope (indoor experiment) to clarify loss pathways of soluble C, N, P and K in biochar-amended soils. Wood biochar pyrolized at 300 ​°C (LWB) or 600 ​°C (HWB) was applied at 1% (LWB1; HWB1) or 2% (LWB2; HWB2). Our results show that the pathways for C, N, P and K loss was percolation ​> ​surface runoff ​> ​soil erosion. Compared to control, HWB2 treatment had a 2–4 times higher infiltration amount but 5–6 times lower surface runoff and soil loss, indicating that this treatment alleviated nutrient loss via erosion and runoff in the sloped soil. Among all treatments, HWB2 treatment was the most effective for retaining organic C, dissolved organic C, total N, and exchangeable K through various pathways. However, a substantial amount of soluble P was lost through percolation. Therefore, the potential pollution of groundwater by P through percolation pathway should be considered during biochar application.

Continuous streamflow prediction in ungauged basins: long short-term memory neural networks clearly outperform traditional hydrological models

Abstract. This study investigates the ability of long short-term memory (LSTM) neural networks to perform streamflow prediction at ungauged basins. A set of state-of-the-art, hydrological model-dependent regionalization methods are applied to 148 catchments in northeast North America and compared to an LSTM model that uses the exact same available data as the hydrological models. While conceptual model-based methods attempt to derive parameterizations at ungauged sites from other similar or nearby catchments, the LSTM model uses all available data in the region to maximize the information content and increase its robustness. Furthermore, by design, the LSTM does not require explicit definition of hydrological processes and derives its own structure from the provided data. The LSTM networks were able to clearly outperform the hydrological models in a leave-one-out cross-validation regionalization setting on most catchments in the study area, with the LSTM model outperforming the hydrological models in 93 % to 97 % of catchments depending on the hydrological model. Furthermore, for up to 78 % of the catchments, the LSTM model was able to predict streamflow more accurately on pseudo-ungauged catchments than hydrological models calibrated on the target data, showing that the LSTM model's structure was better suited to convert the meteorological data and geophysical descriptors into streamflow than the hydrological models even calibrated to those sites in these cases. Furthermore, the LSTM model robustness was tested by varying its hyperparameters, and still outperformed hydrological models in regionalization in almost all cases. Overall, LSTM networks have the potential to change the regionalization research landscape by providing clear improvement pathways over traditional methods in the field of streamflow prediction in ungauged catchments.

Rainstorms impacts on water, sediment, and trace elements loads in an urbanized catchment within Moscow city: case study of summer 2020 and 2021

In 2020 and 2021, the city of Moscow, Russia, has experienced two historical rainfall events that had caused major flooding of small rivers. Based on long-term observation datasets from the surrounding weather stations, regional mesoscale COSMO-CLM climate model results, and a detailed hydrological and water quality monitoring data, we performed a pioneer assessment of climate change and urbanization impact on flooding hazard and water quality of the urban Setun River as a case study. Statistically significant rise of some moderate ETCCDI climate change indices (R20mm and R95pTOT) was revealed for the 1966–2020 period, while no significant trends were observed for more extreme indices. The combined impact of climate change and increased urbanization is highly non-linear and results in as much as a fourfold increase in frequency of extreme floods and shift of water regime features which lead to formation of specific seasonal flow patterns. The rainstorm flood wave response time, involving infiltrated and hillslope-routed fraction of rainfall, is accounted as 6 to 11 h, which is more than twice as rapid as compared to the non-urbanized nearby catchments. Based on temporal trends before and after rainfall flood peak, four groups of dissolved chemicals were identified: soluble elements whose concentrations decrease with an increase in water discharge; mostly insoluble and well-sorted elements whose concentrations increase with discharge (Mn, Cs, Cd, Al); elements negatively related to water discharge during flood events (Li, B, Cr, As, Br and Sr); and a wide range of dissolved elements (Cu, Zn, Mo, Sn, Pb, Ba, La, Cs, U) which concentrations remain stable during rainfall floods. Our study identifies that lack of research focused on the combined impacts of climate change and urbanization on flooding and water quality in the Moscow urban area is a key problem in water management advances.

Fluvial bedrock gorges as markers for Late-Quaternary tectonic and climatic forcing in the Southwestern Alps

Fluvial incision is one of the major erosive processes acting at Earth's surface and is highly sensitive to tectonic, isostatic and climatic variations. The aim of this study is to distinguish between the short-term climatic fluctuations versus the long-term tectonic forcing contribution to Late-Quaternary fluvial incision, to better understand its timing and driving mechanism(s). To achieve this goal, we measured in situ-produced 36Cl concentrations along several river-polished gorge walls in Jurassic limestones of the Southwestern Alps. We then compared our dating results to previously-dated river gorges from nearby catchments. This allows us to highlight three trends of distinct incision dynamics, and to discuss their relationships with climate and tectonics. Trend 1 shows the direct impact of a paraglacial crisis in the rivers connected to glaciated areas. Trend 2 suggests an incision wave propagating along the non-glaciated tributaries following enhanced incision in the main streams. Trend 3 displays steady and low incision rates in gorges disconnected from any fluvial response to glacier retreat. Trend 3 also seems to highlight the potential of resistant lithologies to isolate portions of the river network from post-glacial incision propagation. Our analysis shows that gorges connected to upstream glaciers exhibit a significant response of fluvial incision to climatic fluctuations, evidenced by high-amplitudes incision rate variations hindering the long-term tectonic signal. In contrast, incision rates inferred from disconnected gorges are in agreement with previously-estimated long-term denudation and rock-uplift rates in the area. Based on the latter, we can conclude that Late-Quaternary river incision in the Southwestern Alps is readjusting to both short-term climatic forcing and long-term tectonic forcing.

Lake basins drive variation in catchment‐scale runoff response over a decade of increasing rainfall in Arctic Alaska

AbstractLakes basins cover wide extents of many Arctic Coastal Plain (ACP) landscapes and thus are integral components of hydrological processes. Observed variation in runoff responses between two adjacent catchments being monitored pre‐ and post‐development in the National Petroleum Reserve in Alaska (NPR‐A) suggested the need to better understand how lake basins, both current lakes and drained lake basins (DLBs), modify flow regimes. A progressive increase in summer rainfall over this monitoring period, 2009–2019, also provided an opportunity to assess how watershed characteristics interacted with hydrologic intensification. Stream gauging records from eight other nearby catchments ranging from 16 to 270 km2 with varying extents of lakes (14%–47%) and DLBs (5%–57%) expanded our analysis of ACP hydrology. Wider DLB extent corresponded to higher and more rapid snowmelt peak flows and this relationship also became evident during rainstorms in summers with high antecedent surface storage. Mean annual runoff and summer low‐flows were best explained by extent of connected lakes. Over this period of increasing summer rainfall, all hydrograph responses became more closely related to the full extent of lake basins suggesting expanding connectivity. Our final year of complete hydrologic records in 2019 was punctuated by a 30‐mm late‐summer rainfall event, which generated flow peaks nearly exceeding snowmelt runoff at several gauges, specifically ones with high extent of DLBs. This rain‐event response underscored the increasing need to include both lakes and DLBs in models of ACP watershed hydrology. An improved understanding of catchment‐scale controls on variable hydrologic responses will be increasingly essential for mitigating hazards to new and existing development, predicting floods, drought, and water supply, and protecting aquatic ecosystem functioning and habitat as the Arctic hydrologic cycle intensifies and development expands.

Dynamic parameterization of soil surface characteristics for hydrological models in agricultural catchments

The detrimental impacts of surface runoff and soil erosion, particularly in cultivated areas, call for the use of distributed runoff and soil erosion models with a view to supporting adapted catchment management strategies. However, runoff model parameterization remains challenging in agricultural catchments due to the high spatial and seasonal variability of soil properties. Data acquisition is demanding and may not always be feasible. Therefore, model parameterization in such environments have been the subject of numerous research efforts. The combined analysis of land use management and soil surface state was proposed in literature to address this issue and demonstrated its potential for runoff analysis and modelling. However, these research findings were related to specific rainfall sequences and/or soil surface state. In this study, existing knowledge on soil surface state and its application to runoff model parameterization were synthetized and included in an easy-to-use parameterization software (PREMACHE), providing a framework for modelers lacking of means and/or data for modelling complex agricultural catchments.To develop and evaluate the software, a dataset was acquired over 9 years on more than 110 plots in a 1045 ha agricultural catchment, including crop types, soil surface state, rainfall and runoff time series. Soil surface state dynamics was modeled based on crop types and daily rainfall. It was evaluated in the experimental catchment and validated in a nearby catchment. Soil hydrodynamic properties (e.g. infiltration capacity) were deduced from this framework and literature data at a daily time step, for each plots. Moreover, runoff events were measured when the modeled infiltration capacity was low, indicating that the parametrization adequately captured its temporal dynamics. The software developed in this study, as well as setup values deduced from the monitoring campaigns are provided with the manuscript for application in other ungauged catchments and explore their impact on agricultural catchment hydrological dynamics.

History of slope instability in the Oldina plantation, Tasmania

Background: This paper describes a landslide swarm generated by exceptionally high two-day rainfall (c. 300 mm) associated with a stationary cut-off low pressure system over northern Tasmania in early June 2016 and investigates evidence for previous slope instability. The landslide swarm occurred in a recently harvested plantation in the Inglis River catchment at Oldina, south of Wynyard in north-west Tasmania. Within a relatively small area of plantation underlain by weathered Permian tillite and minor siltstones more than thirty rapid earthflows, rotational and translational landslides occurred. Many landslides also occurred in the nearby Forth and Mersey River catchments. Methods: Field observations combined with a digital elevation model produced from high-resolution drone imagery were used to describe the morphology of the Oldina landslides, and to calculate the mass of soil, sediment, and woody debris displaced. Radiocarbon dating of charcoal exposed in landslide backwalls enabled palaeo-landslides and periglacial activity at Oldina to be dated. Results: An estimated 48,400–72,310 t of soil, sediment and woody debris was carried downslope by the major landslides but has been retained within the plantation area. The total sediment loss from the affected upper catchments is likely to be greater than the above estimate as the contribution from small riparian landslides, sheet, gully, and rill erosion has not been accounted for, nor has streambank erosion and sediment transported off the study site been measured. Radiocarbon dating of charcoal in sediments indicated that two landslides had evidence of previous instability in the Holocene. Most ages indicated that previous instability dated to 35–15 cal ka BP, i.e., to a time when the climate was cold and dry and freeze-thaw processes in a sparsely vegetated landscape were active. Conclusions: During planning for harvest the soils developed on Permian tillite were correctly described as having a low to moderate risk of landslide erosion. This study concludes that the landslides initiated in June 2016 resulted from exceptionally heavy rain falling on harvested steep and hilly land coupled with the decline in root strength of the harvested trees. The frequency of such a combination of circumstances may increase if high-intensity rainfall increases in Tasmania as the result of climate change. To improve the long-term stability of this terrain and the overall sustainability of plantation forestry it is recommended that landslides and riparian areas are seeded with native vegetation, and that the current assessment of landslide risk for this terrain is re-evaluated.

Ryanair market strategies to assert dominance in the European low-cost airline market?

The European minimal expense transporters have delighted in sensational development lately and have significantly modified the organization of short-pull air administrations gave. Interest for minimal expense administrations has demonstrated more unstable than in the US, nonetheless, and there are beginning signs that the transporters' capacity to animate traffic is decreasing. Numerous new contestants have gotten on board with that temporary fad, and the conventional aircrafts have begun to retaliate. An examination of various courses from London shows that the minimal expense transporters have been significantly more fruitful in certain business sectors than others. The significant aircrafts stay predominant in areas including their primary centre air terminals though flimsy courses inside northern Europe have shown little development from minimal expense transporter section, some leftover the safeguard of territorial transporters. The minimal expense aircrafts have performed best on thick courses not including significant air terminals and relaxation courses among northern and southern Europe. Serious procedures that are inspected incorporate the capacity of minimal expense aircrafts to draw in rush hour gridlock to optional and provincial air terminals that were beforehand underutilized. It is shown that on certain courses from significant urban communities, optional air terminals are currently dealing with a greater part of the neighbourhood travellers. Notwithstanding, the capacity of air terminals to develop past the traffic capability of their own nearby catchment region decreases as additional areas gain minimal expense administration. Albeit a few undiscovered open doors might stay in nations like France and for administrations with more modest airplane, new courses are having a tendency to weaken existing interest. The centre is consequently prone to go to more straight on contest in the denser business sectors.

The variation and controls of mean transit times in Australian headwater catchments

AbstractDetermining mean transit times in headwater catchments is critical for understanding catchment functioning and understanding their responses to changes in landuse or climate. Determining whether mean transit times (MTTs) correlate with drainage density, slope angle, area, or land cover permits a better understanding of the controls on water flow through catchments and allows first‐order predictions of MTTs in other catchments to be made. This study assesses whether there are identifiable controls on MTTs determined using 3H in headwater catchments of southeast Australia. Despite MTTs at baseflow varying from a few years to &gt;100 years, it was difficult to predict MTTs using single or groups of readily‐measured catchment attributes. The lack of readily‐identifiable correlations hampers the prediction of MTTs in adjacent catchments even where these have similar geology, land use, and topography. The long MTTs of the Australian headwater catchments are probably in part due to the catchments having high storage volumes in deeply‐weathered regolith, combined with low recharge rates due to high evapotranspiration. However, the difficulty in estimating storage volumes at the catchment scale hampers the use of this parameter to estimate MTTs. The runoff coefficient (the fraction of rainfall exported via the stream) is probably also controlled by evapotranspiration and recharge rates. Correlations between the runoff coefficient and MTTs in individual catchments allow predictions of MTTs in nearby catchments to be made. MTTs are shorter in high rainfall periods as the catchments wet up and shallow water stores are mobilized. Despite the contribution of younger water, the major ion geochemistry in individual catchments commonly does not correlate with MTTs, probably reflecting heterogeneous reactions and varying degrees of evapotranspiration. Documenting MTTs in catchments with high storage volumes and/or low recharge rates elsewhere is important for understanding MTTs in diverse environments.

Predicting flood insurance claims with hydrologic and socioeconomic demographics via machine learning: Exploring the roles of topography, minority populations, and political dissimilarity

Current research on flooding risk often focuses on understanding hazards, de-emphasizing the complex pathways of exposure and vulnerability. We investigated the use of both hydrologic and social demographic data for flood exposure mapping with Random Forest (RF) regression and classification algorithms trained to predict both parcel- and tract-level flood insurance claims within New York State, US. Topographic characteristics best described flood claim frequency, but RF prediction skill was improved at both spatial scales when socioeconomic data was incorporated. Substantial improvements occurred at the tract-level when the percentage of minority residents, housing stock value and age, and the political dissimilarity index of voting precincts were used to predict insurance claims. Census tracts with higher numbers of claims and greater densities of low-lying tax parcels tended to have low proportions of minority residents, newer houses, and less political similarity to state level government. We compared this data-driven approach and a physically-based pluvial flood routing model for prediction of the spatial extents of flooding claims in two nearby catchments of differing land use. The floodplain we defined with physically based modeling agreed well with existing federal flood insurance rate maps, but underestimated the spatial extents of historical claim generating areas. In contrast, RF classification incorporating hydrologic and socioeconomic demographic data likely overestimated the flood-exposed areas. Our research indicates that quantitative incorporation of social data can improve flooding exposure estimates.

Sediment-related water quality of small hill-country streams near Whatawhata, New Zealand. Response to integrated catchment management (ICM)

ABSTRACT Degradation of aquatic ecosystems by fine sediment is a global environmental problem, and damages reflect particle properties as well as mass concentration. We studied sediment-related water quality (SRWQ) of small streams in hill-country near Whatawhata, NZ, that have been monitored since 1995. In 2001, an integrated catchment management (ICM) plan was implemented in the Mangaotama (originally sheep-beef) catchment – including conversion of steep headwaters to pine plantation, cattle exclusion, and native riparian plantings. The long-term SRWQ within the Mangaotama catchment was examined with reference to a nearby native-forested control catchment. Correlations between visual clarity, suspended particulate matter concentration and related variables were moderate to fairly strong. The ICM has not improved SRWQ as expected – plausibly because removal of cattle disturbance has been offset by decline in pasture ground cover under increasing shade of tree plantings. Worsening SRWQ is expected over the next several decades as channels widen towards a ‘forest’ morphology.

Origin, geomorphology and geoheritage potential of Australia’s longest coastal cliff lines

Two spectacular cliff lines occur along Australia’s south and west coasts: the Great Southern Scarp (new name) and the Zuytdorp Cliffs. Detailed measurements of their length show that they are exceptionally long and unusually continuous. The Great Southern Scarp is the southern edge of the Nullarbor Plain’s Bunda Plateau; it is cut into shallow marine sediments and extends for 820 km. Once a continuous sea-cliff, local uplift has isolated two sections from the ocean, so it now comprises the Bunda Cliffs (210 km of coastal cliff, 180 km of which is uninterrupted cliff line), Hampton Range (inland; 300 km), Baxter Cliffs (160 km of coastal cliff) and Wylie Scarp (inland; 160 km). The Zuytdorp Cliffs are coastal cliffs cut into eolianite, and extend for 210 km with an uninterrupted section of 120 km. The length of the Great Southern Scarp and the Zuytdorp Cliffs results from an unusual combination of circumstances. They are both composed of poorly jointed, relatively homogenous biogenic calcarenites, presented to high-energy ocean waves by regional uplift. The carbonates are sufficiently well cemented to maintain a steep vertical cliff face, but susceptible to disintegration under direct wave attack. Cliff retreat has been fairly uniform because of the broad spatial scale of both lithology and erosion. The arid climate, absence of nearby non-karstic catchments and karstic nature of the cliffs’ hinterlands has discouraged integrated drainage development, so no significant fluvial systems dissect the cliffs; this is a key factor in cliff edge preservation. In the case of the Great Southern Scarp, these processes have formed the longest continuous cliff line in Australia and probably the world. Referenced against criteria from Australia’s National Heritage List, the cliffs have potentially international/national levels of significance for the rarity of their scale, their demonstration of landscape evolution, and their spectacular beauty.KEY POINTSAustralia’s longest coastal cliffs, the Bunda (SA) and Zuytdorp (WA) cliffs, are equal in length (210 km, within defined confidence levels).The Bunda Cliffs are part of the Great Southern Scarp (new name), an 820 km-long feature of the Nullarbor Plain that also includes the coastal Baxter Cliffs (160 km in length) and two paleocoastal scarps.The unusual continuity of the cliff lines results from a landscape history specific to the Australian continent, and the Great Southern Scarp is likely to be unusual on a global scale.The Great Southern Scarp and the Zuytdorp Cliffs have potentially national and/or international levels significance for geoheritage values in the criteria of events and processes, rarity and aesthetics.

Scheduling Supplementary Irrigation for Maize Production: Analysis of the Requirements for Climate Smart Farming for Rural Development

The erratic rainfall pattern in sub Saharan Africa is a major threat to rainfed agriculture by consistently reducing yield due to water deficit and threatening food security. In order to address this problem, supplementary irrigation during the raining season is increasingly being encouraged to reduce water deficits during dry spells. The aim of this study is to design a supplementary irrigation for maize cropping during the raining season by using climatic data and water from surface runoff from a nearby catchment area. Climatic data for the study area was used to analyse the water requirement of maize during the rainy season and to propose an irrigation schedule. The results indicated that, out of 620.00 mm (3100 m3) water requirement for the entire growing cycle of maize on a 0.5 ha field, the supplementary irrigation water requirement represents more than a third of the water need of maize during periods of dry spell in the maize crop cycle. With a reservoir volume of 600.00 m3 and a net irrigation application of 60 mm (300 m3), about 5 irrigation applications (with a flow rate of 25.00 m3/hr for 6 hours a day) is required to supplement the irrigation water requirement of maize that can help alleviate soil moisture stress and increase crop yield during critical growth stages.

Historic development of heavy metal contamination into the Firth of Thames, New Zealand

Near-coastal marine sediments often provide high-resolution records of various anthropogenic influences such as the release of heavy metals, which pose a potentially negative influence on aquatic ecosystems because of their toxicity and persistence. In places, the gradual onset of man-made heavy metal emission dates back to ~ 4500 years BP and is difficult to distinguish from potential natural sources. New Zealand offers a perfect setting for studies on anthropogenic impact due to its well-defined three-step development: pre-human era (until ~ 1300 CE), Polynesian era (~ 1300–1800 CE) and European era (since ~ 1840 CE). However, hardly any information exists about the degree of heavy metal input to New Zealand’s coastal areas and the ‘pristine’ natural background values. This study determines the natural background contents of lead (Pb) and zinc (Zn) in marine sediments of the Firth of Thames, a shallow marine embayment on New Zealand’s North Island, and investigates anthropogenic inputs in historic times. Eight sediment cores were analysed by X-ray fluorescence (XRF) for their element composition and temporally resolved by a pollen and radiocarbon-based stratigraphic framework. Sharp increases in Pb and Zn contents occurred simultaneously with the onset of goldmining activities (1867 CE) in the nearby catchment area. The contents of Zn (Pb) increase from very stable values around 60 (13) ppm in the older sediments, interpreted to reflect the natural background values, to an average maximum of 160 (60) ppm near the core top, interpreted to reflect a significant anthropogenic input. These findings unravel the history of contamination in the Firth of Thames and provide an urgently needed database for the assessment of its current ecological state.

Selection of appropriate loss methods in HEC-HMS model and determination of the derived values of the sensitive parameters for un-gauged catchments in Northern Ethiopia

ABSTRACTThe estimation of peak flood and runoff is important in planning water development and flood mitigation/adaptation works. This can be simplified by using calibrated hydrological models, yet in many developing country situations there is a paucity of primary flow data. Against this background, the current study was undertaken in an un-gauged catchment in Northern Ethiopia. The study was aimed at deriving values of the sensitive parameters of the HEC-HMS model that could be transferred to similar geographical settings. To calibrate the model, observed data were collected using a rated current meter for flow and manual rain gauges for precipitation. The spatial characteristics of the study area were processed using HEC-GeoHMS, as an ArcGIS extension. To simulate runoff volume and peak flow, two kinds of loss methods in HEC-HMS model were tested, and the parameters CN (curve number) and constant loss rate were found the most sensitive parameters. From this, improved simulation results (NSE of 88% and R2 of 0.89) were obtained in a model set contained initial and constant loss method and SCS unit hydrograph. It is suggested that the methodology and results of the study could be further used in simulation of runoff in the catchment and other nearby catchments as an aid to planning.

A Comparison of Methods for Calculating Monthly Flows on Small Catchments

The paper deals with a determination of the monthly time series of flows in catchments where this quantity is not measured. While determining unknown flows, the authors have assumed that the historical climatic data for the given area and flows in nearby and similar catchments are available. So-called “analogy” methods are possible to use for such a defined task. In these methods, unknown flows are determined based on an “analogy” with known data from similar, nearby catchments. The authors have compared hydrological modelling and statistical and machine learning regression methods. They have determined that if at least short-term measurements are available for the river catchment studied, the most suitable method is a regression with LASSO regularisation, as LASSO eliminates the problem of multicollinearity in the input data. The use of the Support Vector Machines and Neural Network with Bayesian regularisation seems to be other suitable methods. The precision of hydrological modelling results is slightly less than the results from regression methods, but the authors have demonstrated that these results are still suitable in the context of water management calculations.

Soil moisture response to rainfall on the Chinese Loess Plateau after a long‐term vegetation rehabilitation

AbstractThe Chinese Loess Plateau (CLP) is a unique Critical Zone with deep loess deposits, where soil moisture is primarily replenished by seasonal monsoon rainfall. However, the role of vegetation, coupled with complex topography, on rainwater infiltration on the CLP, especially after long‐term revegetation for controlling erosion, is inadequately quantified. Over the growing season of 2016, we monitored soil moisture at the 30‐min interval at 5 depths (10, 20, 40, 60, and 100 cm) in an afforested catchment and a nearby catchment with natural regrowth of grasses. Two monitoring sites were established in each catchment, one in the downhill gully and the other in the uphill slope. We found that vegetation, topography, and rainfall attributes together determined rainwater infiltration and soil moisture replenishment. An accumulated rainfall amount of 9 mm was required to trigger soil moisture response at 10‐cm depth at the 2 grassland sites and the forestland uphill‐slope site whereas 14 mm of rainfall was required for the forestland gully site covered by dense undergrowth and trees. Rainfall events with larger sums and higher peak intensities permitted rainwater infiltration to deeper soil depths. However, no rain recharged soil moisture to 100‐cm depth during the monitoring period. The forestland uphill‐slope site showed the deepest wetting depth (up to 60‐cm depth), fastest wetting‐front velocity (up to 4 cm/hr below 10‐cm depth), and the most significant soil moisture increase (up to 15% cm 3 cm−3 increase at 10‐cm depth) after rainfall in the growing season. The grassland gully site had the highest soil water storage, whereas soil moisture was depleted the most at the forestland gully site. Findings of this study reveal the transient dynamics of soil moisture after rainfall on the CLP, which signifies the role of revegetation on rainwater infiltration in the loess Critical Zone.

Preliminary assessment of heavy metals in water, sediment and macrophyte (Lemna minor) collected from Anchar Lake, Kashmir, India

Water samples, sediments and free floating macrophytic plant, Lemna minor specimens were collected from five designated sites in Anchar lake (Srinagar, J&K, India) to assess its heavy metal (Cu, Cr, Zn, Ni, Cd, Pb) load and changes on seasonal basis. The concentration of heavy metals was determined using atomic absorption spectroscopy. Most of the samples were found within limits of maximum permissible concentrations as recommended by WHO (Guidelines for drinking water quality, pp 491–493, 2006). During all the seasons, highest concentration of all heavy metals (Cu, Cr, Zn, Ni, Cd, Pb) was recorded at highly polluted sites of the lake viz. near agricultural fields (S1), near settlements (S3) and SKIMS (S4). These sites received huge agrochemical run-off from the surrounding agricultural fields, solid and liquid wastes from the nearby catchment areas and effluents from Sher-e-Kashmir Institute of Medical Sciences (SKIMS) compared to control site lake centre (S5). Furthermore, most of the metals in water and sediment were found with highest concentration during autumn (Viz., Cu-1.5 ppm; Zn-0.38 ppm; Ni-1.89 ppm; Pb-0.84 ppm in water and Cu-26.9 ppm; Zn-13.6 ppm; Pb-4.33 ppm in sediment) and summer (Viz., Cr-0.68 ppm in water and Ni-4.8 ppm; Cd-2.6 ppm; Cr-8.01 ppm in sediment) seasons. Also in Lemna minor plant highest concentration was observed during summer season (Cu-29.09 ppm; Zn-19.11 ppm; Ni-5.7 ppm; Cd-1.34 ppm; Cr-9.18 ppm and Pb-9.77 ppm). From these observations, it was found that the sources of heavy metals in Anchar lake were both natural and anthropogenic ones. This study recommended that continuous monitoring of heavy metals (Viz; Cu, Cr, Zn, Ni, Cd and Pb) in water, sediment and other aquatic biota of Anchar lake should be directed to protection of ecological status of the lake and its surrounding area.