Small Drainage Basins Research Articles

Using sediment rating parameters to evaluate the changes in sediment transport regimes in the middle Yellow River basin, China

AbstractThis study analyses the changes in sediment transport regimes in the middle Yellow River basin (MYRB) using sediment rating parameters. Daily streamflow and suspended sediment concentration data were collected at 35 hydrological stations from the 1950s to 2016, which can be divided into three periods based on the type and intensity of human activities: the base stage before 1970, the restraining stage from 1971 to 1989, and the restoration stage after 2002. Data within each period were fitted by log‐linear sediment rating curves and the sediment rating parameters were utilized to analyse the spatial and temporal variations in sediment transport regimes. The results show that sediment rating parameters are indicative of sediment transport regimes. In the base stage and the restraining stage, the hydrological stations can be categorized into four groups based on their locations on the rating parameter plot. The stations with small drainage basins were characterized by the highest sediment transport regime, followed by those located in the coarse‐particle zone, the loess zone, and the mountainous/forest zone. In the restoration stage, the difference in sediment transport regimes between different geomorphic zones became less distinguishable than in previous stages. During the transition from the base stage to the restraining stage, sediment rating parameters showed no significant changes in sediment transport regimes in all four geomorphic groups. During the transition from the restraining stage to the restoration stage, significant changes were observed in the coarse‐particle zone and the mountain/forest zone, indicating that the revegetation programme and large reservoirs imposed a stronger influence on sediment transport regimes in these two zones than in the rest of the MYRB. This study provides theoretical support for evaluating sediment transport regimes with sediment rating parameters.

Peak Flows and Stormwater Networks Design—Current and Future Management of Urban Surface Watersheds

Stormwater urban drainage systems are typically designed in open channel flow. Pipe sewers must have enough capacity to transport maximum design flows for a given frequency of the project rainfall. The classic rational method or related procedures that are based on rational approaches are still currently used to a great extent, particularly for small urban drainage basins, and the pipes are frequently designed in uniform steady flow. Numerical integration of Saint-Venant equations for one-dimensional gradually varied unsteady flow allows the computation of waves’ progression along the pipes for given input surface hydrographs. This paper presents a comprehensive, systematic, simple, and original comparison between the peak flows that are achieved through simulation in unsteady flow using an implicit complete dynamic model, developed in the Laboratory of Hydraulics, Water Resources and Environment of Coimbra University, and those that are obtained with the classic rational method along urban drainage networks. Boundary conditions and some approximations typically considered in the methodologies are analyzed in detail. Classic rational approaches may underestimate the peak and design flows. Practical recommendations for the system design phase when rational approaches are used are also proposed. The need for indispensable requirements for suitable urbanization rules, intelligent management of surface runoff in urban basins, and control measures for the reduction of peak flows entering existing networks is confirmed and reinforced.

GENESIS AND PHYSICAL CHARACTERISTICS OF THE NEOGENE RED BEDS FROM THE CEDARHILS OF THESSALONIKI, MACEDONIA , GREECE

The genesis and the physical characteristics of the Neogene red beds of the cedar hills surrounding Thessaloniki are studied in this paper. The peri-urban forest, which covers these hills, has a 3,022 ha area. The topographic relief is smooth and is divided in eight small drainage basins, tapped through small creeks. The elevation of the surrounding hills varies between 85 and 560 m. The dominant land slopes vary between 20 and 55%. All the samples are coarse grained, poorly sorted and friable and present earthy lustre and red colour because of the extensive presence of iron oxides. Angular to sub-angular rock fragments derived from the metamorphic bedrock are very common. Petrographically, the studied red beds belong to the clayey sands. The extended presence (41-66%) of coarse silt and sand size grains (>20 pm) in the samples suggests a mild intensity of in situ weathering of the bedrock. X-ray diffraction analysis of the coarsest fractions 250-20 pm and 20-2 μιτι revealed in decreasing abundance the presence of quartz, feldspars, epidote, micas, chlorite, pyroxenes, amphiboles, and talc. These fractions contain the 2M polytype of mica, while in the fraction <2 pm the 1Μα polytype of illite predominates. In the clay fraction (<2 pm) illite, smectite, and chlorite predominate. The presence of mixed-layer minerals is limited, testifying the almost complete character of hydrolysis of the primary minerals. The formation of red beds took place on low relief land under alternating wet and dry seasons, which prevail in the eastern Mediterranean region since Neogene. The clay minerals are the in situ weathering products of the primary minerals of the greenschists, gneisses and gabbros predominating in the studied area. The extensive presence of clay size grains (11-26%) in the samples, their poor sorting, and their sub-angular morphology, indicate that the red beds are texturally immature. In addition, the abundance of feldspars and Fe-Mg minerals reflects mineralogical immaturity. The low relief and the long-lasting tectonic stability in the Thessaloniki district were essential for the significant thickness of the red beds. The oxygen isotope data of the <0.2 pm fraction (+18.2 to +18.8%o) confirm the pedogenic origin of the clay minerals present. The red beds studied present low plasticity with liquid limit (WÏ) 26.9 to 33.4% and plasticity index (lp) 9.1 to 17.3%. In addition, they have high consolidation index (lc) values (1.03 to 2.28). The swelling potential is low to medium and the activity varies between 0.5 and 1.0. The consolidation and induration degree of the samples analyzed is low, because of the great range of their mineralogical composition and the mild conditions of pressure and temperature to which they have been submitted. The studied red beds are not considered problematic for the foundation of various constructions on them.

Flash floods simulation in a small drainage basin using HEC-RAS hydraulic model

Abstract In recent years, climate conditions has caused extreme hydrological phenomena like flash floods that lead to significant material losses and impact on the environment in Dobrogea Region, Romania. In this context the needs for an integrated and sustainable approach to flash flood risk management even in small drainage basins are necessary, in order to reduce the the potential damages of flash floods in the future. In this study the hydraulic models Hec-Ras and HecGeo-Ras were used in order to simulate the behaviour of the environment at the pressure of the flashfloods in a small drainage basin. The results were validated using the measurements undertaken after the flash-flood event recorded in October, 13th, 2015 as well as the data provided by the Corbu gauging station along time.

Sedimentary processes on the continental slope off Kvitøya and Albertini troughs north of Nordaustlandet, Svalbard – The importance of structural-geological setting in trough-mouth fan development

New marine-geophysical data were analyzed to investigate the sedimentary processes operating on the continental slope north of Nordaustlandet, Svalbard. Kvitøya Trough terminates in a trough-mouth fan (TMF) on the slope, whereas Albertini Trough incises the shelf edge and a TMF is notably absent. Instead, the continental slope beyond Albertini Trough is dominated by thick, acoustically stratified units likely formed by down-slope and along-slope sedimentological processes combined. The morphological and sedimentological differences between Albertini and Kvitøya troughs may partly be due to the larger dimensions of Kvitøya Trough and its associated glacial catchment area relative to Albertini, suggesting that the transport of a larger volume of glacigenic sediments potentially was a contributing factor in building Kvitøya TMF. By contrast, the downfaulted bedrock below outer Albertini Trough provided larger accommodation space for glacigenic sediments which accumulated in an outer-shelf basin, highlighting the importance of the structural-geological setting in TMF development. Debris-flow deposits and/or channel-levee deposits on the lower continental slope and rise off Kvitøya Trough indicate bypassing of glacigenic sediments from the shelf to the deep ocean, a process that is likely a result of locally steep slope gradients (<9°). The volume of the Kvitøya TMF is smaller than TMFs along the western Svalbard margin, which may be linked to the more erosion-resistant bedrock of the northern margin and/or the comparatively small drainage basin of Kvitøya Trough compared to drainage basins of ice streams that drained westwards from Barents Sea. In addition, the Kvitøya TMF is incised by gullies indicating that they formed after Last Glacial Maximum (LGM) while larger tributary canyons flanking the Kvitøya TMF likely have developed during a longer time span. High seafloor backscatter values in the tributary canyons and gullies are interpreted as coarse-grained deposits that lead down-slope to debris-flow deposits, suggesting an origin for the tributary canyons and gullies through incision by gravity flows of sediment-laden meltwater during and/or after deglaciation.

Agricultural land use doubled sediment loads in western China’s rivers

Abstract Land use changes, such as deforestation and agricultural expansion, increase soil erosion on the scale of hillslopes and small drainage basins. However, the effects of these changes on the sediment load in rivers is poorly quantified, with a few studies scattered globally, and only 10 data points in the world’s most populous nation, China. At 20 different sites in western China, we compare contemporary fluvial sediment yield data collected daily over 4 to 26 years between 1945 and 1987 (median = 19 years) to long-term measures of sediment generation based on new isotopic measurements of in situ 10Be (beryllium-10) in river sediments. We find that median sediment yield at these sites exceeds background sediment generation rates by a factor of two (from 0.13 to 5.79 times, median 1.85 times) and that contemporary sediment yield is statistically significantly different from long-term sediment generation rates (p

Mechanism of removal and retention of heavy metals from the acid mine drainage to coastal wetland in the Patagonian marsh

The attenuation of the acid mine drainage is one of the most important environmental challenges facing the mining industry worldwide. Mining waste deposits from an ancient metallurgical extraction of heavy metals were found near to the San Antonio marsh in Patagonia. The aim of this work was to determinate which mechanisms regulate the mobilization and retention of metals by acid drainage. A geological and geomorphological survey was carried out and samples from the mining waste deposits and the marsh were collected to determine soil texture, Eh pH, organic matter, Cu, Pb, Zn and Fe content, and soil mineralogical composition. Metals in marsh plants were determined in above- and below-ground structures. In the mining waste deposits polymetallic sulphides were recognized where the oxidation and formation of oxy-hydroxides and sulphates of Fe, Cu, Pb and Zn occurs. Then, by the alteration of those minerals, the metals enter in solution and are mobilized with the surface drainage towards the marsh where adsorption in the soils fine fraction and organic matter and/or by plants occurs. Locally, in the mining waste deposits, the precipitation/dissolution of Cu, Pb, and Zn sulphates take place in small centripetal drainage basins. In topographically lower portions of the marsh desorption and removal of metals by tidal flow could also be happen. The results allow to concluding that the marsh adjacent to the mining waste deposits is a geochemically active environment that naturally mitigates the contamination caused by acid drainage.

Sources and dispersal of land-based runoff from small Hawaiian drainages to a coral reef: Insights from geochemical signatures

Land-based sediment and contaminant runoff is a major threat to coral reefs, and runoff reduction efforts would benefit from knowledge of specific runoff sources. Geochemical signatures of small drainage basins were determined in the fine fraction of soil and sediment, then used in the nearshore region of a coral reef-fringed urban embayment on southeast Oahu, Hawaii, to describe sources and dispersal of land-based runoff. The sedimentary rare earth element ratio (La/Yb)N showed a clear distinction between the two main rock types in the overall contributing area, tholeiitic and alkalic olivine basalt. Based on this geochemical signature it was apparent that the majority of terrigenous sediment on the reef flat originated from geologically old tholeiitic drainages. Sediment from one of five tholeiitic drainages had a distinct geochemical signature, and sediment with this signature was dispersed on the reef flat 2 km west and 150 m offshore of the contributing basin. Sediment and the anthropogenic metals Cd, Pb, and Zn were entrained in runoff from the most heavily urbanized region of the watershed. Although anthropogenic Cd and Zn had localized distributions close to shore, anthropogenic Pb was found associated with fine sediment on the westernmost part of the reef flat and 400 m offshore, illustrating how trade-wind-driven sediment transport can increase the scale of runoff impacts to nearshore communities. Our findings show that sediment geochemical signatures can provide insights about the source and dispersal of land-based runoff in shallow coastal environments. The application of such knowledge to watershed management and habitat remediation efforts can aid in the protection and restoration of runoff-impacted coastal ecosystems worldwide.

Analysis of relationships among coastal alluvial fans and their contributing catchments in North Evoikos Gulf (Central Greece).

This paper deals with the morphometric analysis of 42, late Holocene, coastal alluvial fans located along the coasts of the tectonically active North Evoikos Gulf in central Greece. Thirty six of the fans have been formed by streams that discharge along the east coast of the Gulf (Evia Island) while the rest are located on the opposite side (Continental Greece). Selected morphometric parameters of the drainage basins were measured using topographic maps at the scale of 1:50,000 while those of the fans were derived from detailed topographic diagrams at the scale of 1:5,000 utilizing ESRI’s ArcGIS9.3 software. Fans were classified into four groups according to the primary depositional processes (fluvial and/or debris flow). Another classification criterion was the relationship between the location of the fan-catchment system and the local tectonic patterns (active faults). Fan-basin morphometric relationships for each fan group were also investigated. A strong positive relation was found between the size of the fan and the drainage basin area while the correlation between drainage area and fan slope was negative. Large catchments located near fault terminations have formed gently sloping fans dominated by fluvial processes, whereas torrents with small rough drainage basins, developed on the footwall, have formed steep fans likely dominated by debris-flow along the east coast of the Gulf

Preliminary characterization of slope stability in a small basin in the South-West of Sardinia (Italy)

The assessment of slope instability in small drainage basins is relevant because their impacts affecting population and infrastructure are usually very fast and sometimes destructive. This study presents the methodological approach to assess the stability of a small granitic river basin located in the South-West of Sardinia (Italy). In the drainage area two different kinds of slope deposits, originated at different times, were analysed. In order to determine the origin and evolution of the different deposits, the bodies of the moved masses and the head scarps were respectively characterized through profiles, grain size analysis and geomechanic classification. The profiles were surveyed using Jacob staff or Abney level. The survey tape method was applied to determine the grain size distribution (GSD) in cross sections at each slope deposit. The GSD was analysed using standard statistics. The geomechanical characterization of the cliffs in the headscarps above the deposits were made using Bieniawski (1979) and Romana (1985) methods. The former deposits have a regular longitudinal profile. The plan form can be convex or slightly concave. They are formed by cobbles and boulders and they are matrix free. They were classified as debris slope (DS).The cliff above the DS was evaluated vulnerable to plane failure and completely unstable. The new deposit hillslope gradient and transversal sections are irregular. It is formed by cobbles, boulders and pebbles, it has matrix of granules sand and silt. It is a complex mass movement between rock fall and rock avalanche (RF-RA).The cliff above the RF-RA is vulnerable to plane failure and toppling and is partially stable.

Hydrological Modeling and Characterization of the Khanpur Watershed, Pakistan

The Khanpur watershed in Pakistan has a high spatial changeability of precipitation attributable to extremely undulating surface topography and complex interactions between the land elevation and precipitation. This study used stormwater runoff modeling software, adapted to determine peak discharge of the Haro River. Correlation analysis was used to select input precipitation data for the software. Horton's and Strahler's strategies were used for manipulating the streams’ analysis and characterization of the watershed. Morphological features of the watershed are important in terms of hydrology. The bifurcation ratio was 3.5, which showed that the watershed has suffered less structural disturbance and the drainage patterns have not been distorted. The stream density of 0.5 is low, demonstrating a lower flood risk and an average channel slope. The Khanpur watershed has a circularity ratio of 0.6, showing that it is a small drainage basin with homogeneous geologic material that preserves the geometrical similarity. It has been determined that the watershed is well drained, hilly, and slopey.

Historical erosion and sedimentation in two small watersheds of the southern Blue Ridge Mountains, North Carolina, USA

Sediment bodies produced during historical periods of human land use, sometimes referred to as legacy sediment, may be found in various locations within drainage basins, and potentially remobilized by hydrogeomorphic processes accompanying land use change. The amounts and locations of stored legacy sediment can be significant factors in modern drainage basin function and should be accounted for when possible. In this study, late nineteenth-century erosion and sediment storage were investigated and used to construct approximate sediment budgets for two small Blue Ridge Mountain drainage basins in North Carolina (USA). Erosion was quantified using a distributed implementation of the Universal Soil Loss Equation (USLE), and calibrated on the separate bases of soil profile truncation data and recent published rates for long-term erosion in the region. Sediment yield information was reconstructed from pond sediments trapped behind a mill dam. Alluvial sediment storage was quantified using field studies of streambank and floodplain sediment profiles and digital elevation data. Colluvial storage was calculated as a residual in the sediment budget, and further evaluated using soil profile studies of footslope deposits, and soil survey maps. The proportions of erosion accounted for by the different budget terms in the most reliable budget are: 28% sediment yield (i.e., a sediment delivery ratio of 0.28), 69% colluvial storage, and 3% alluvial storage. Blue Ridge basins with low levels of ground disturbance erode like Piedmont basins at high levels of ground disturbance, primarily due to higher slope angles. Sediment delivery ratio is high relative to those given for much larger basins in the adjacent and more frequently studied Piedmont province, and generally in accordance with published sediment delivery curves that reflect higher hydrogeomorphic connectivities within smaller basins. Low values for alluvial storage in Blue Ridge basins may be explained by high sediment transport within steep channels. Colluvial storage values have high uncertainties because of the well known problem of error accumulation in residual budget terms. Field data on colluvial deposits reported here are not sufficient to correct for this problem, and in general, the acquisition of accurate field data on historical colluviation remains an important methodological issue in historical sediment budgeting.

Flood forecasting and alert system for Arda River basin

Summary The paper presents the set-up and functioning of a flood alert system based on SURFEX–TOPODYN platform for the cross-border Arda River basin. The system was built within a Bulgarian-Greek project funded by the European Territorial Cooperation (ETC) Programme and is in operational use since April 2014. The basin is strongly influenced by Mediterranean cyclones during the autumn–winter period and experiences dangerous rapid floods, mainly after intensive rain, often combined with snow melt events. The steep mountainous terrain leads to floods with short concentration time and high river speed causing damage to settlements and infrastructure. The main challenge was to correctly simulate the riverflow in near-real time and to timely forecast peak floods for small drainage basins below 100 km 2 but also for larger ones of about 1900 km 2 using the same technology. To better account for that variability, a modification of the original hydrological model parameterisation is proposed. Here we present the first results of a new model variant which uses dynamically adjusted TOPODYN river velocity as function of the computed partial streamflow discharge. Based on historical flooding data, river sections along endangered settlements were included in the river flow forecasting. A continuous hydrological forecast for 5 days ahead was developed for 18 settlements in Bulgaria and for the border with Greece, thus giving enough reaction time in case of high floods. The paper discusses the practical implementation of models for the Arda basin, the method used to calibrate the models’ parameters, the results of the calibration-validation procedure and the way the information system is organised. A real case of forecasted rapid floods that occurred after the system’s finalisation is analysed. One of the important achievements of the project is the on-line presentation of the forecasts that takes into account their temporal variability and uncertainty. The web presentation includes a comparison of the forecasted river flow to three predefined alert levels.

Morphometry and Flood in Small Drainage Basin: Case Study of Mayogwoi River Basin in Jalingo, Taraba State Nigeria

Morphometry and Flood in Small Drainage Basin: Case Study of Mayogwoi River Basin in Jalingo, Taraba State Nigeria

The Impact of Drought on Streamflow and Stream-Aquifer Exchange in the Upper Neosho River, Kansas

Meteorological drought in the Great Plains of the U.S. has a significant influence on the hydrology of small drainage basins. Its effect on local surface water and groundwater systems is complicated when streamflow is regulated by flood-control reservoirs. An analysis of local precipitation, discharge, and groundwater records on annual, monthly, and daily intervals in the upper Neosho River of Kansas demonstrates the importance of frequent, small-scale monitoring to resource management. Natural, drought-induced, noflow conditions prior to reservoir construction were eliminated by sustained, low-volume, reservoir outflow over five drought cycles. Temporary bank storage, caused by reservoirinduced, high-flow pulses, was observed at the Emporia State University Campus Woods field station during a prolonged recent drought. Gaining and losing stream conditions were observed in multi-year monitoring but, in drought years, losing conditions occurred only when reservoir releases generated stream flow. In drought and non-drought years, relatively low groundwater levels coincided with seasonal growing periods, reflecting the importance of transpiration by riparian vegetation on stream-aquifer exchange. An understanding of the drought response of the individual elements of a floodplain hydrologic system is important to management of the integrated resource.

River restoration by dam removal: Enhancing connectivity at watershed scales

Abstract The prolonged history of industrialization, flood control, and hydropower production has led to the construction of 80,000 dams across the U.S. generating significant hydrologic, ecological, and social adjustments. With the increased ecological attention on re-establishing riverine connectivity, dam removal is becoming an important part of large-scale river restoration nationally, especially in New England, due to its early European settlement and history of waterpower-based industry. To capture the broader dimensions of dam removal, we constructed a GIS database of all inventoried dams in New England irrespective of size and reservoir volume to document the magnitude of fragmentation. We compared the characteristics of these existing dams to the attributes of all removed dams over the last ∼25 years. Our results reveal that the National Inventory of Dams significantly underestimates the actual number of dams (4,000 compared to &amp;gt;14,000). To combat the effects of these ecological barriers, dam removal in New England has been robust with 127 dams having been removed between ca. 1990–2013. These removed dams range in size, with the largest number (30%) ranging between 2–4 m high, but 22% of the removed dams were between 4–6 m. They are not isolated to small drainage basins: most drained watersheds between 100–1,000 km2. Regionally, dam removal has re-connected ∼3% (3,770 river km) of the regional river network although primarily through a few select dams where abundant barrier-free river lengths occur, suggesting that a more strategic removal approach has the opportunity to enhance the magnitude and rate of river re-connection. Given the regional-scale restoration of forest cover and water quality over the past century, dam removal offers a significant opportunity to capitalize on these efforts, providing watershed scale restoration and enhancing watershed resilience in the face of significant regional and global anthropogenic changes.

LATE GLACIATION AND HOLOCENE DEVELOPMENT OF THE EROSION- ACCUMULATION PROCESSES IN THE SMALL BASINS OF THE WESTERN TRANSBAIKALIA

Detailed investigations of soil-sediment sequences of three sections (Nizhnyaya Bulanka, Nadeino and Kuytun) in the Kuytunka river basin (Western Transbaikalia) was carried out. Three stages of activation of erosion- accumulation processes in small drainage basins of Western Transbaikalia are determined: Pre Holocene (13.0– 10.7), Early- (10.3–8.0) and Late Holocene (last 2.5 14C kyr). During these stages several phases of sedimentation and soil-forming process are distinguished. High intensity of aeolian processes together with washout and sedimentation during time spans of 10.7–10.0 and 9.5–9.0 kyr were determined on erosion landforms and alluvial fans. The main causes of deposition processes intensification have been revealed and quantitative data about their intensity were obtained. Intensification of soil-forming process in conditions of mountain-forest-steppe landscapes of Western Transbaikalia begins when sedimentation rates reach 0.06–0.37 mm/yr. Within the sedimentation rate interval 0.3–0.6 mm/yr humus interlayers alternate with layers of colluvial and aeolian deposits. At the rate above 0.6 mm/yr sedimentation of sandy loam and sands with inclusions of rubble are observed. Duration of soil development is 300–3500 years. Sediment accumulation phases have duration from 70 to 2000 years. Development of erosion-accumulation processes are characterized by polychronicity related to different response of small drainages basins to global, regional and local environmental changes. Rhythmical development of the washout, erosion, accumulation and soil-forming processes provides long-term activity of erosional landforms.

HIERARCHY OF SMALL DRAINAGE BASINS

Hierarchy of small drainage basins, conditions and factors of their forming, and typical processes on every hierarchic level are examined. The following spatiotemporal hierarchic levels have been distinguished: 1) slopes and bottoms of small drainage basins; 2) elementary basins; 3) single small drainage basins; 4) regional types of small drainage basins. Compiled spatiotemporal matrix shows how objects of investigation are distributed in accordance to their hierarchy. Every hierarchic level has its own complex of processes. Present day level deals with segments of small drainage basins, which are exposed to weather conditions. Anthropogenic activity reaches its maximum importance on the historical interval. Level of geological time intervals deals with great regional units, where climatic and tectonic conditions, rock features, etc are the most important factors. As a result, the necessity for selecting particular methods for every hierarchic level during investigation of small drainage basins is shown.

Upscaling Nitrogen Removal Capacity from Local Hotspots to Low Stream Orders’ Drainage Basins

Denitrification is the main process removing nitrate in river drainage basins and buffer input from agricultural land and limits aquatic ecosystem pollution. However, the identification of denitrification hotspots (for example, riparian zones), their role in a landscape context and the evolution of their overall removal capacity at the drainage basin scale are still challenging. The main approaches used (that is, mass balance method, denitrification proxies, and potential wetted areas) suffer from methodological drawbacks. We review these approaches and the key frameworks that have been proposed to date to formalize the understanding of the mechanisms driving denitrification: (i) Diffusion versus advection pathways of nitrate transfer, (ii) the biogeochemical hotspot, and (iii) the Damkohler ratio. Based on these frameworks, we propose to use high-resolution mapping of catchment topography and landscape pattern to define both potential denitrification sites and the dynamic hydrologic modeling at a similar spatial scale (<10 km2). It would allow the quantification of cumulative denitrification activity at the small catchment scale, using spatially distributed Damkohler and Peclet numbers and biogeochemical proxies. Integration of existing frameworks with new tools and methods offers the potential for significant breakthroughs in the quantification and modeling of denitrification in small drainage basins. This can provide a basis for improved protection and restoration of surface water and groundwater quality.

Exceptional floods on a developed river: case study for the Bistrita River from the Eastern Carpathians (Romania)

The geographical position of the Bistrita River favours a rich liquid run-off and great hydrotechnical potential. The Bistrita drainage basin is strongly developed from the hydrotechnical point of view. Within the drainage basin, numerous dams and storage reservoirs are installed with the purpose of producing electricity and reducing flood hazards. However, these structures could not stop floods at the drainage basin level. The most powerful floods from Bistrita River basin and the role in flood control of each of the storages are analysed in this paper. The hydrological data have been collected from the monitoring network, where the researchers elaborating this study are performing their daily activity. The most powerful floods in the last century took place in 1970, 1991, 2005 and 2010. An intensification of the floods can be noticed after the year 1990, a period which coincides with large-scale deforestation of the small drainage basins. Disastrous floods occurred as a consequence of summer heavy rains, with amounts of 100–200 mm within 24 h. The most powerful floods were recorded in 2005 and registered discharges up to 1,200 m3/s. Izvoru Muntelui reservoir, the biggest in the system, can take most of the waters in excess. The reservoirs located downstream are silting up, and the supplementary flows cannot be absorbed entirely by storage. The exact knowledge of flooding phenomena requires studies that can prevent and diminish the damages caused by extreme hydrological events.