Small Catchment Size Research Articles

Streamflow maps for run-of-river hydropower developments in Japan

Japan recently introduced a feed-in tariff for small-scale hydropower plants, promoting the development of run-of-river hydropower plants in small-sized basins; however, appropriate implementation requires gauging station streamflow data at substantial costs and time (i.e., more than several years). Thus, in this study, we generated streamflow maps for small-sized basins (∼10 km2) throughout Japan using artificial neural networks (ANNs). Modeled output streamflow characteristics relied upon the input variables obtained from 176 basin characteristics and consisted of mean annual streamflow (QMEAN), daily streamflow indices in a flow duration curve (QD), and a water volume index for run-of-river hydropower energy production (WD95). We preliminarily investigated the impacts of selecting the input variables obtained from 176 basin characteristics on performances of the ANNs, which indicated that the ANNs showed high robustness for disinformative input variables and multicollinearity between input variables. Although QMEAN, high QD, and WD95 performed well, low QD were inadequate, possibly due to snowmelt contributions and small catchment sizes obstructing the detection of geological impacts. To accurately estimate the streamflow characteristics throughout Japan, we emphasize the importance of developing robust methods for correcting wind-induced precipitation undercatch and a spatial interpolation for precipitation in high-montane areas. Nevertheless, the ANNs for Japan proposed herein significantly outperformed a previous study exhibiting excellent global-scale ability. A map expressing run-of-river hydropower potential in small-sized basins was generated and closely corresponded to the spatial distribution and electrical output of existing hydropower plants. Furthermore, we demonstrated that the hydropower potential map reproduces the hydropower developments corresponding to the history of the electric power systems in Japan, which reflects its high reliability. Therefore, the hydropower potential map can greatly aid the exploration of optimal sites for hydropower developments.

The use of wetted perimeter as habitat proxy to assess environmental flows in Southern Quebec rivers (Canada)

Environmental flows assessment in eastern Canada, and particularly in the province of Quebec, is mainly based on hydrological assessment of historical data during low flow periods. The mean 7-day low flow with return periods of two (7Q2) and ten years (7Q10) are two flow metrics currently used by the Quebec Department of Environment and Fight against Climate Change to prescribe minimum flow and/or maximum water abstraction while maintaining the functions and health of riverine ecosystems. This study investigated the use of the wetted perimeter as an additional environmental flows assessment method. This tool can be used by water managers to maintain the availability of river habitats during low flow periods. Twenty flow metrics were computed for inter-annual, summer and winter periods, for 43 sites from 35 rivers, and analysed to study the changes in wetted perimeter with flow. In addition, the flow associated with maximum curvature (breakpoint) of the flow-wetted perimeter function (QMC) was analyzed. Results provided a better understanding of local changes of river hydraulics and possible aquatic habitat availability associated with different flow metrics. The relevance of using a wetted perimeter threshold (WPSQMC) combined with flow thresholds (Tennant method) was also discussed. The two “fair” Tennant flow thresholds, apart from the twenty flow metrics, would provide sufficient available habitat all year long with corresponding WPSQMC thresholds of 88% and 95% of the 43 river sites. The median discharge for August flow metric for summer and the median discharge for the month with the lowest flow metric value for winter (usually February), provided the highest wetted perimeter in relative terms (72% and 79% respectively of the river sites) compared to the WPSQMC threshold. Using the 7Q2 flow metric would mean maintaining sufficient available habitat for 50%, 60% and 72% of the river sites for respectively inter-annual, summer and winter periods. Considering the single WPSQMC threshold, its associated flow provided the highest values for 16% of the river sites and the second highest one for 9% of the river sites with a single seasonal flow metric value high enough for summer or winter. This study showed that the wetted perimeter is a tool providing additional information on both river morphology and changes in potential aquatic habitat as a function of flow for river sites with small catchment size and low mean annual flow values. Indeed, the wetted perimeter can be very useful in the overall assessment of environmental flows.

Dissolved inorganic carbon export by mountainous tropical rivers of the Western Ghats, India

Large rivers that are known for carrying huge fluxes are few in numbers; nevertheless, the contributions of thousands of small mountainous coastal rivers to global biogeochemical cycles is also measured to be equally important. Small catchment sizes, high channel gradients yet high water discharge are prominent characters of the coastal rivers draining the Western Ghats (WG) of India. Three geo-tectonic divisions, namely, Southern Granulite Terrain (SGT) in southern, Western Darwar Craton (WDC) in central and Deccan Traps (DT) in the north constitute the entire Western Ghats. Based on the seasonal sampling of 70 coastal rivers draining into the Arabian Sea, this study provides a comprehensive discharge-weighted estimate of DIC for the Western Ghats (WG) region. The concentration of bicarbonate measured in-situ using gran plot method. Fluxes and yields were calculated using seasonal discharge and area of respective rivers. The discharge-weighted DIC concentration of WG region is 629 μM, which is slightly higher than the average global DIC concentration for the low latitude (< 30°) rivers. Despite, covering 113×103km2 area, this region yearly exports 175×109 mol DIC to the Arabian Sea. The DIC flux contributed by the WG region is among the highest in peninsular rivers and comparable with several large global rivers. DIC export rates suggest that within the region, the chemical weathering rate of DT is ∼4 times and WDC is ∼2.5 times higher than that of SGT region. The DIC flux of the WG region (covering 0.076% of global land area) is approximately 0.55% of the global riverine DIC flux to the ocean. Thus, in terms of global DIC export to seas, this region is the 28th largest contributor. Due to high annual DIC yield (1547×103 mol km−2) WG region ranks as the 9th most active region of the world. DIC yields of rivers draining granite-dominated (SGT and WDC) and basalt-dominate (DT) regions of WG are remarkably higher than the global rivers draining similar lithology from temperate and arctic regions. The WG rivers display a latitudinal gradient in DIC transport. Type of silicate rocks, rainfall-runoff, temperature range, and sediment yields control the variability in DIC fluxes and export rates of Western Ghats region.

Are catchments leaky?

AbstractCatchments, generally understood as the drainage areas of low‐order streams, are often regarded as closed hydrologic entities; that is, precipitation (P) minus evapotranspiration (ET) over a catchment equates stream outflow (Q r). Here, we review evidence that catchments can be leaky due to groundwater outflow or inflow across topographic divides, based on catchment mass balance across a continent and several site‐based studies across the globe. It appears that a catchment is more likely to be leaky with the combination of the following factors: small catchment size, positioned at either the high or low end of a steep regional topographic and climatic gradient, underlain by deep permeable substrates that extend beyond the study catchment, and in drier climate or dry seasons and droughts. Catchment leakage has hydrological, geochemical, and ecological implications. Thus, catchments are best framed as semiclosed hydrologic units perched on top of a larger, regional hydrogeological system with no real boundaries regarding the movement of water and solutes.This article is categorized under: Science of Water &gt; Hydrological Processes Water and Life &gt; Nature of Freshwater Ecosystems

Age–depth relationship and accumulation rates in four sediment sequences from the Retezat Mts, South Carpathians (Romania)

This study summarizes the results of radiocarbon dating and age-depth modelling in four mountain lakes (Brazi, Gales, Bucura and Lia) in the Retezat Mountains. Altogether 69 AMS 14C measurements were performed on these deposits, mostly on terrestrial plant macrofossils. In several cases, plant macrofossils, aquatic animal remains (Cladoceran eggs) and bulk sediment were measured from the same depth allowing for the comparison of various sediment components in terms of their dating potential. Age-depth models were developed using both Bayesian modelling with the BACON and smooth spline curve fitting with the CLAM software. In this study Bayesian models are applied to identify outlier 14C dates, while smooth spline models are used to model sediment accumulation age-depth relations, as these are more likely to follow natural deposition time changes of lake sediments. Changes in sediment deposition times (DT) in relation to catchment size and climate are also studied.DT varied considerably in the late glacial (LG) part of the records. The sediment sequence characterised by high deposition rates during the late glacial (DT maximum around 100–110 years cm−1) was defined by small catchment size (Lake Brazi, 6 ha; surface area: 0.5 ha). In contrast, much slower LG sediment deposition in the southern slope lake characterised by large catchment area (Lake Lia, 171 ha, 20 years cm−1), principally reflecting strong erosion in these catchment areas at times when vegetation cover was scarce. Holocene was characterised again by variable DT values, but only Lake Gales showed extreme values: 62–110 years between 10,900 and 6050 cal yr BP, followed by much slower sediment deposition in the last 6000 years (av. 29 years cm−1). Generally, sediment deposition times were largely dependent on the stability and vegetation cover of the slope in the case of high altitude deep lakes, while lower altitude, shallow lakes showed slower sediment deposition time in the early and mid-Holocene, when summer insolation was higher than today. This reflects that in these shallow lakes in-lake organic production probably increased with summer insolation, which was a significant driver in the rate of deposition.

Fresh meteoric versus recirculated saline groundwater nutrient inputs into a subtropical estuary

The role of groundwater in transporting nutrients to coastal aquatic systems has recently received considerable attention. However, the relative importance of fresh versus saline groundwater-derived nutrient inputs to estuaries and how these groundwater pathways may alter surface water N:P ratios remains poorly constrained. We performed detailed time series measurements of nutrients in a tidal estuary (Hat Head, NSW, Australia) and used radium to quantify the contribution of fresh and saline groundwater to total surface water estuarine exports under contrasting hydrological conditions (wet and dry season). Tidally integrated nutrient fluxes showed that the estuary was a source of nutrients to the coastal waters. Dissolved inorganic nitrogen (DIN) export was 7-fold higher than the average global areal flux rate for rivers likely due to the small catchment size, surrounding wetlands and high groundwater inputs. Fresh groundwater discharge was dominant in the wet season accounting for up to 45% of total dissolved nitrogen (TDN) and 48% of total dissolved phosphorus (TDP) estuarine exports. In the dry season, fresh and saline groundwater accounted for 21 and 33% of TDN export, respectively. The combined fresh and saline groundwater fluxes of NO3, PO4, NH4, DON, DOP, TDN and TDP were estimated to account for 66, 58, 55, 31, 21, 53 and 47% of surface water exports, respectively. Groundwater-derived nitrogen inputs to the estuary were responsible for a change in the surface water N:P ratio from typical N-limiting conditions to P-limiting as predicted by previous studies. This shows the importance of both fresh and saline groundwater as a source of nutrients for coastal productivity and nutrient budgets of coastal waters.

Hydrological model comparison and assessment: criteria from catchment scales and temporal resolution

ABSTRACTThis study examines the performance of three hydrological models, namely the artificial neural network (ANN) model, the Hydrologiska Byråns Vattenbalansavdelning-D (HBV-D) model, and the Soil and Water Integrated Model (SWIM) over the upper reaches of the Huai River basin. The assessment is done by using databases of different temporal resolution and by further examining the applicability of SWIM for different catchment sizes. The results show that at monthly scale the performance of the ANN model is better than that of HBV-D and SWIM. The ANN model can be applied at any temporal scale as it establishes an artificial precipitation–runoff relationship for various time scales by only using monthly precipitation, temperature and runoff data. However, at daily scale the performance of both HBV-D and SWIM are similar or even better than the ANN model. In addition, the performance of SWIM at a small catchment size (less than 10 000 km2) is much better than at a larger catchment size. In view of climate change modelling, HBV-D and SWIM might be integrated in a dynamical atmosphere-water-cycle modelling rather than the ANN model due to their use of observed physical links instead of artificial relations within a black box.Editor D. Koutsoyiannis; Associate editor D. Hughes

Tectonic geomorphology at small catchment sizes – extensions of the stream-power approach and the &amp;lt;i&amp;gt;χ&amp;lt;/i&amp;gt; method

Abstract. Quantitative tectonic geomorphology hinges on the analysis of longitudinal river profiles. The model behind almost all approaches in this field originates from an empirical relationship between channel slope and catchment size, often substantiated in the form of the stream-power model for fluvial incision. Significant methodological progress was recently achieved by introducing the χ transform. It defines a nonlinear length coordinate in such a way that the inherent curvature of river profiles due to the increase of catchment sizes in the downstream direction is removed from the analysis. However, the limitation to large catchment sizes inherited from the stream-power approach for fluvial incision persists. As a consequence, only a small fraction of all nodes of a digital elevation model (DEM) can be used for the analysis. In this study we present and discuss some empirically derived extensions of the stream power law towards small catchment sizes in order to overcome this limitation. Beyond this, we introduce a simple method for estimating the adjustable parameters in the original χ method as well as in our extended approaches. As a main result, an approach originally suggested for debris flow channels seems to be the best approximation if both large and small catchment sizes are included in the same analysis.

Analysis of flash flood parameters and human impacts in the US from 2006 to 2012

Summary Several different factors external to the natural hazard of flash flooding can contribute to the type and magnitude of their resulting damages. Human exposure, vulnerability, fatality and injury rates can be minimized by identifying and then mitigating the causative factors for human impacts. A database of flash flooding was used for statistical analysis of human impacts across the U.S. 21,549 flash flood events were analyzed during a 6-year period from October 2006 to 2012. Based on the information available in the database, physical parameters were introduced and then correlated to the reported human impacts. Probability density functions of the frequency of flash flood events and the PDF of occurrences weighted by the number of injuries and fatalities were used to describe the influence of each parameter. The factors that emerged as the most influential on human impacts are short flood durations, small catchment sizes in rural areas, vehicles, and nocturnal events with low visibility. Analyzing and correlating a diverse range of parameters to human impacts give us important insights into what contributes to fatalities and injuries and further raises questions on how to manage them.

Multi-trophic resilience of boreal lake ecosystems to forest fires.

Fires are the major natural disturbance in the boreal forest, and their frequency and intensity will likely increase as the climate warms. Terrestrial nutrients released by fires may be transported to boreal lakes, stimulating increased primary productivity, which may radiate through multiple trophic levels. Using a before-after-control-impact (BACI) design, with pre- and postfire data from burned and unburned areas, we examined effects of a natural fire across several trophic levels of boreal lakes, from nutrient and chlorophyll levels, to macroinvertebrates, to waterbirds. Concentrations of total nitrogen and phosphorus were not affected by the fire. Chlorophyll a levels were also unaffected, likely reflecting the stable nutrient concentrations. For aquatic invertebrates, we found that densities of three functional feeding groups did not respond to the fire (filterers, gatherers, scrapers), while two groups increased (shredders, predators). Amphipods accounted for 98% of shredder numbers, and we hypothesize that fire-mediated habitat changes may have favored their generalist feeding and habitat ecology. This increase in amphipods may, in turn, have driven increased predator densities, as amphipods were the most numerous invertebrate in our lakes and are commonly taken as prey. Finally, abundance of waterbird young, which feed primarily on aquatic invertebrates, was not affected by the fire. Overall, ecosystems of our study lakes were largely resilient to forest fires, likely due to their high initial nutrient concentrations and small catchment sizes. Moreover, this resilience spanned multiple trophic levels, a significant result for ecologically similar boreal regions, especially given the high potential for increased fires with future climate change.

Establishing rainfall depth–duration–frequency relationships at daily raingauge stations in Hong Kong

Summary Rainfall intensity (depth)–duration–frequency (IDF/DDF) relationships provide information essential for urban stormwater drainage system design and other hydrosystem infrastructures. For catchments where drainage areas are small, rainfall DDF relationships with short duration can be established based on rainfall records from automatic raingauges. Due to the progression of technology development, wide spread installation of automatic raingauges does not happen until 2–3 decades ago. Therefore, record lengths at majority of automatic raingauges are relatively short and the derived rainfall DDF relationships on the basis of at-site frequency analysis are potentially subject to significant sampling error. On the other hand, many conventional raingauges exist long before automatic raingauges were deployed. However, daily rainfall data with long records at conventional raingauges are of limited use to establish rainfall DDF relationships in areas with small catchment size like Hong Kong where design storm duration significantly shorter than 24-h are needed. This study presents a practical methodological framework to derive rainfall DDF relationships with short duration at conventional raingauge locations. The core components of the framework include the scaling model of rainfalls of different durations, the establishment of relationship between annual maximum daily rainfall and rolling-time 1440 min rainfall, the quantification of statistical features of estimated annual maximum 1440 min rainfalls, and the assessment of uncertainty of derived rainfall DDF relationships at conventional raingauges.

Uncertainty-based calibration and prediction with a stormwater surface accumulation-washoff model based on coverage of sampled Zn, Cu, Pb and Cd field data

A dynamic conceptual and lumped accumulation wash-off model (SEWSYS) is uncertainty-calibrated with Zn, Cu, Pb and Cd field data from an intensive, detailed monitoring campaign. We use the generalized linear uncertainty estimation (GLUE) technique in combination with the Metropolis algorithm, which allows identifying a range of behavioral model parameter sets. The small catchment size and nearness of the rain gauge justified excluding the hydrological model parameters from the uncertainty assessment. Uniform, closed prior distributions were heuristically specified for the dry and wet removal parameters, which allowed using an open not specified uniform prior for the dry deposition parameter. We used an exponential likelihood function based on the sum of squared errors between observed and simulated event masses and adjusted a scaling factor to cover 95% of the observations within the empirical 95% model prediction bounds. A positive correlation between the dry deposition and the dry (wind) removal rates was revealed as well as a negative correlation between the wet removal (wash-off) rate and the ratio between the dry deposition and wind removal rates, which determines the maximum pool of accumulated metal available on the conceptual catchment surface. Forward Monte Carlo analysis based on the posterior parameter sets covered 95% of the observed event mean concentrations, and 95% prediction quantiles for site mean concentrations were estimated to 470 μg/l ±20% for Zn, 295 μg/l ±40% for Cu, 20 μg/l ±80% for Pb and 0.6 μg/l ±35% for Cd. This uncertainty-based calibration procedure adequately describes the prediction uncertainty conditioned on the used model and data, but seasonal and site-to-site variation is not considered, i.e. predicting metal concentrations in stormwater runoff from gauged as well as ungauged catchments with the SEWSYS model is generally more uncertain than the indicated numbers.

Radar‐based flood forecasting in small catchments, exemplified by the Goldersbach catchment, Germany

Although draining an area of only 75 km2, the Goldersbach caused several times severe flooding in the city of Tubingen, Germany. To cope with this, a flood management was set up based on flood forecasting, partial retention in reservoirs and local flood protection. Due to the small catchment size, the anticipated flood‐forecast lead time of three hours could only be achieved by using local, weather‐radar based rainfall forecasts for the next 1.5 hours. In short‐term rainfall forecasting, knowledge of the current rainfield advection is crucial. Therefore, two advection estimation techniques were applied: one based on the Doppler effect the other on covariance maximization. To combine the advantages of the available sources of rainfall observation, namely radar and rain gauges, a method for ‘geostatistical merging’ was developed. It preserves both the relatively reliable mean rainfall measurements from the rain gauges and the high spatial resolution of the radar image. Based on the advection estimates, a short‐term, auto‐regressive forecast model (SCM, or Spectrum‐Corrected Markov chain model) was developed. It follows a two‐step hierarchical approach. A bivariate, auto‐regressive process forecasts the large‐scale development of rainfall in a radar image. The individual development of each gridcell in the image is forecasted by a Markov chain approach. Finally, two rainfall‐runoff models are used for short‐term flood forecasting. The first, Fgmod, is an event‐based model, the second, HBV‐IWS, is a continuous water balance model. Both rainfall‐runoff models, in combination with the rainfall forecast, allow reasonable discharge estimates for up to three hours.

Analysis of the formation and failure of Ram Creek landslide dam, South Island, New Zealand

During the May 1968 Inangahua earthquake, a 2.8 × 106 m3 landslide dam was formed in highly weathered granitic material in the headwaters of Ram Creek on the West Coast of the South Island, New Zealand. The landslide dam impounded a lake immediately upstream of the dam for c. 13 yr without breaching. The dam crest was breached on 29 April 1981 during an intense rainstorm, resulting in complete and catastrophic failure of the Ram Creek landslide dam. A dambreak flood caused substantial damage downstream. The longevity of the dam was probably due to its resistance to internal erosion, the small size of catchment, and the lack of high intensity/long duration rainfall in the catchment area. Three internationally derived geomorphic indices (Impoundment Index, Blockage Index, and Dimensionless Blockage Index) used to predict the stability (post‐formation dam development) of landslide dams were applied to the Ram Creek landslide dam; all three indices correctly predicted the short term (< 12 yr) development of the dam but failed to predict the catastrophic failure some 13 yr after formation. It is impossible to predict when a sufficiently intense event will cause overtopping failure of a landslide dam. It is conceivable that the Ram Creek dam could have remained intact for many more decades if the 1981 storm had been a little less intense, or centred a few kilometres farther away. Hence, the stability of this landslide dam was essentially a statistical concept, because the event against which it is stable is stochastic in nature.

On the Meteorological Mechanisms Driving Postfire Flash Floods: A Case Study

Abstract This paper describes work to improve the understanding of the broad range of factors affecting the occurrence of postfire flooding, with emphasis on an event that occurred in the Alpine Shire, Victoria, Australia, in 2003. Analysis and mesoscale modeling of the conditions surrounding the event suggests that the drivers of the extreme rainfall event were above-average precipitable water in the atmosphere, significant values of CAPE, producing strong updrafts within the thunderstorm capable of supporting large quantities of suspended water droplets, and thunderstorm cell regeneration in the same area. However, atmospheric instability was further enhanced by anabatic breezes, above-average boundary layer moisture, and increased surface heating resulting from reduced surface albedo and soil moisture of the recently burned fire surface. Flash flooding resulted, due to 1) the storm cells likely being pulse wet microbursts, 2) cell regeneration over the same area (very little horizontal movement), and 3) the small catchment size. It is likely that a further contributor to the observed flash flood was the reduced infiltration often observed in recently burned catchments; these factors will be explored in a subsequent hydrologic study. It is intended that the mechanisms elucidated in this study will assist in emergency preparedness in the Alpine Shire. Given the warmer conditions expected with near-term anthropogenic climate change for the Alpine Shire, and the concomitant increase in fires, this causal relationship, even for a relatively rare event, has implications for emergency managers and Alpine Shire residents.

Channel processes following land use changes in a degrading steep headwater stream in North Island, New Zealand

In headwater streams in steep land settings, narrow and steep valley floors provide closely coupled relationships between geomorphic components including hillslopes, tributary fans, and channel reaches. These relationships together with small catchment sizes result in episodic changes to the amount of stored sediment in channels. Major sediment inputs follow high magnitude events. Subsequent exponential losses via removal of material can be represented by a relaxation curve. The influence of hillslope and tributary processes on relaxation curves, and that of altered coupling relations between components, were investigated along a 1.3 km reach of a degrading channel in the 4.8 km 2 Weraamaia Catchment, New Zealand. Extensive deforestation in the late 19th and early 20th centuries, followed by invasion of scrubs and reforestation, induced changes to major erosion types from gully complexes to shallow landslides. Changes in the size and pattern of sediment slugs from 1938 to 2002 were analysed from air photographs tied to detailed field measurement. The rate and calibre of sediment flux changed progressively following substantive hillslope input in a storm in 1938. Subsequently, the channel narrowed and incised, decoupling tributary fans from the main stem, thereby scaling down the size of sediment slugs. As a consequence, the dominant influence on the behaviour of sediment slugs and associated relaxation processes, changed from tributary fans to the type and distribution of bedrock outcrops along the reach.