Hydrograph Analysis Research Articles

Deep-karst aquifer spring-flow trends in a water-limited system, Grand Canyon National Park, USA

Better characterization of the water resources of the Grand Canyon National Park (GRCA) and World Heritage Site, USA, will inform management decisions regarding a proposed water supply intake from Bright Angel Creek (BAC) and will inform the associated forecasts on water security related to climate change and the impact on spring-dependent species. Characterization of the water supply for GRCA was improved through multiyear hydrograph analyses at five springs discharging from the Redwall-Muav (R) aquifer: Roaring Springs, Emmett Spring, At Last Spring, Tapeats Spring, and Abyss River Spring. Comparison of snowmelt response timing and mean recession coefficients among the five springs show no significant differences, indicating similar timing of snowmelt-related discharge and flow regimes across 50 km of horizontal and 1,000 m of vertical distance through the aquifer system. The mean water volumes discharged during snowmelt and the mean annual discharge are significantly different between Roaring Springs, Emmett Spring, Tapeats Spring, and Abyss River Spring. Linear regression analyses indicate no annual trends in any of the evaluated aquifer characteristics for any spring, except for more stable baseflow between recessions at Tapeats Spring. Water budgets calculated for Roaring Springs are imbalanced, suggesting missing outflow components, a need to refine the recharge region through dye trace studies, and inaccurate precipitation and evapotranspiration data, requiring model improvement. Continued hydrograph comparisons, trend analyses, and water budgets for additional years and springs will be useful for future groundwater modeling and for forecasting impacts on the R aquifer.

Performance of Sand and Mixed Sand–Biochar Filters for Treatment of Road Runoff Quantity and Quality

Nature-based solutions and similar natural water retention measures to manage urban runoff are often implemented by cities in order to reduce runoff peaks, catch pollutants, and improve sustainability. However, the performance of these stormwater management solutions is relatively rarely assessed in detail prior to their construction, or monitored and evaluated following implementation. The objective of this study was to investigate the field-scale performance of road runoff filters with respect to the management of stormwater quantity and quality. This study synthesizes data from two intensive measurement surveys after the construction of sand and biochar-amended road runoff filters. The filters were able to strongly control the runoff volume and shape of the hydrograph. The long-term retention was about half that of the water inflow, and a hydrographic analysis showed the significant but strong event-size-dependent detention of runoff in both the sand and the sand–biochar filters. The biochar amendment in the filter showed no clear hydrological impact. The pollutant attenuation of the implemented road runoff filters was modest in comparison with that observed under controlled conditions. The impact of the biochar layer on the effluent water quality was observed as the levels of phosphorous, organic carbon, K, Ca and Mg in the sand–biochar filter effluent increased in comparison with the sand filter.

The Role of Inflow and Infiltration (I/I) in Urban Water Balances and Streamflow Regimes: A Hydrograph Analysis Along the Sewershed‐Watershed Continuum

AbstractUrbanization alters subsurface flow pathways through expansion of sanitary collection and conveyance infrastructure. Inflow and infiltration (I/I) into sewers redistributes slow subsurface flows to fast within‐sewer flows. Acting in concert with connected surface water, redistribution through I/I complicates the net impact of urbanization on streamflow. Elucidation of these processes is key to the characterization and prediction of urban hydrologic cycles. In this study, we collected sanitary sewer flow and streamflow data from 17 sewersheds and 18 watersheds in and around Milwaukee, WI, USA. We compared flow duration curves and baseflow recession characteristics of I/I and streamflow in urban and reference watersheds. Median depth‐normalized I/I (296 mm) was nearly 35% of mean annual precipitation (867 mm), and thereby a major component of the urban drainage budget. I/I flowrates were similar to urban streamflow during high flow events (10th percentile) and larger during intermediate (50th percentile) and low (90th percentile) flow events. Further, I/I recession was slower and more nonlinear in shape than urban streamflow. Increased imperviousness and sewer density were associated with increased high flows, decreased intermediate flows, and quicker streamflow recessions. Sewer density explained more variability in intermediate flows (35%) and baseflow recession rate (49%) than imperviousness (24% and 19% respectively). Based on our findings, I/I takes up valuable volume capacity in sewers, which leads to more frequent overflows and alters streamflow regimes with ecological implications. Thus, I/I should be better considered in the prediction of urban hydrologic fluxes, and the characteristics and hydro‐ecologic impact of I/I should be more thoroughly explored.

Analysis of Peak Flood Discharge in Small-Scale River Flow Area

Purpose: Flood discharge is a critical component in reducing the impact of flooding in a given location. An analytical technique based on a watershed's morphometric properties is a method for those without a gauge, particularly in small-scale watersheds.
 Design/methodology/approach: The synthetic unit hydrograph (HSS) approach is used in this study to analyze flood output. This study was conducted in the Akelaka watershed, a sub-watershed of Tayawi. This analysis relies on spatial and attributes data. A spatial study of watershed morphometric properties was obtained by integrating digital elevation model (DEM) data into geographic information system-based applications (GIS). Meanwhile, using rainfall data from 2019 to 2021, a statistical approach is used to calculate the design rainfall intensity, which is then used as an input variable in the HSS analysis.
 Findings: The findings of hydrographic analysis using Nakayasu HSS demonstrate that the peak flood time (Tp) is 2.8 hours with a maximum flood discharge (Qp) of 56.636 m3/s, 76, 987 m3/s, 88,091 m3/s, and 101,279 m3/s for return periods of two years, five years, ten years, and 25 years.
 Paper type: Research paper

Understanding the hydrological response of a headwater-dominated catchment by analysis of distributed surface–subsurface interactions

We computationally explore the relationship between surface–subsurface exchange and hydrological response in a headwater-dominated high elevation, mountainous catchment in East River Watershed, Colorado, USA. In order to isolate the effect of surface–subsurface exchange on the hydrological response, we compare three model variations that differ only in soil permeability. Traditional methods of hydrograph analysis that have been developed for headwater catchments may fail to properly characterize catchments, where catchment response is tightly coupled to headwater inflow. Analyzing the spatially distributed hydrological response of such catchments gives additional information on the catchment functioning. Thus, we compute hydrographs, hydrological indices, and spatio-temporal distributions of hydrological variables. The indices and distributions are then linked to the hydrograph at the outlet of the catchment. Our results show that changes in the surface–subsurface exchange fluxes trigger different flow regimes, connectivity dynamics, and runoff generation mechanisms inside the catchment, and hence, affect the distributed hydrological response. Further, changes in surface–subsurface exchange rates lead to a nonlinear change in the degree of connectivity—quantified through the number of disconnected clusters of ponding water—in the catchment. Although the runoff formation in the catchment changes significantly, these changes do not significantly alter the aggregated streamflow hydrograph. This hints at a crucial gap in our ability to infer catchment function from aggregated signatures. We show that while these changes in distributed hydrological response may not always be observable through aggregated hydrological signatures, they can be quantified through the use of indices of connectivity.

Spatial Hydrological Analysis on storm water harvesting investigation for sustainable water resources management strategy

AbstractThe water issue has become a frontier of public debate globally due to public awareness of sustainable development. Nigeria's water resources are under serious threat from inadequate catchment management that includes widespread pollution from indiscriminate waste disposal. Stormwater is now recognized as a valuable resource rather than a nuisance, especially in large urban centers. Growing demand for water has exerted pressure on groundwater via dug well and boreholes scattered virtually in every dwelling in Nigeria. This challenge motivated this investigation of the feasibility of harvesting stormwater for due purposes of supplementing water supply and flash flood management. This study aims at quantification of harvestable stormwater and identification of potential capturing sites using Spatial Hydrological Analysis of GIS model and Synthetic Hydrograph. The result indicated total harvestable stormwater for 24-hr rainfall of 161.3 Mm3 and three available capturing sites of eight depressions identified. This volume is a good incentive to incorporate storm harvesting in overall water resources sustainable management.

LiDAR DTM Application for Flood Inundation Modeling and Visualization (Case Study: Batu City, East Java)

LiDAR DTM has been widely used for simulating flood inundation from river overflows. This flood inundation simulation needs to be done as an alternative step in the flood control system and flood disaster mitigation to determine the estimated area affected by the flood. Flood simulation is a form of unsteady flow that is simulated with the HEC-RAS program that allows the user to perform one-dimensional steady flow, one and two-dimensional unsteady flow calculations, sediment transport/mobile bed computations, and water temperature/water quality modeling, and visualizes flooded areas and flood-affected areas using a geographic information system approach. Hydrological data is obtained from daily rainfall processing at the time of station rain. Hydrograph analysis was performed using the SCS CN model on the HEC-HMS software to estimate the flow rate and peak discharge. Watershed area, curve number, Impervious value, Initial ion, and time lag are parameters that affect hydrograph analysis. From the results of the hydrograph analysis, the peak discharge of the model is 119.992 m2/s. Meanwhile, hydraulic analysis using HEC-RAS resulted in an inundation of 364 m2 which inundated three villages, namely Bulukerto, Bumiaji and Sidomulyo villages. The depth of the inundated area ranged from 0-15 m with an average depth of 4.534 m. The Sidomulyo area affected by the flood inundation scenario is 4,924 meters with an area of 0,02 ha. Bumiaji village was flooded with an area of 0,007 ha with a scenario of inundation depth of 4,049 m. Bulukerto village which was affected by the flood has an area of 20,972,832 m2 with a scenario of inundation depth reaching 4,343 m. Then some land cover such as residential land that is inundated by this flood simulation is 0,002 ha. Buildings from residential areas that were flooded reached 209 buildings. Then the area of agricultural land affected is 0,02 ha. In addition, there are also green open spaces affected by this simulation with an inundation area of 0,003 ha.

Karst spring recession and classification: efficient, automated methods for both fast- and slow-flow components

Abstract. Analysis of karst spring recession hydrographs is essential for determining hydraulic parameters, geometric characteristics, and transfer mechanisms that describe the dynamic nature of karst aquifer systems. The extraction and separation of different fast- and slow-flow components constituting a karst spring recession hydrograph typically involve manual and subjective procedures. This subjectivity introduces a bias that exists, while manual procedures can introduce errors into the derived parameters representing the system. To provide an alternative recession extraction procedure that is automated, fully objective, and easy to apply, we modified traditional streamflow extraction methods to identify components relevant for karst spring recession analysis. Mangin's karst-specific recession analysis model was fitted to individual extracted recession segments to determine matrix and conduit recession parameters. We introduced different parameter optimization approaches into Mangin's model to increase the degree of freedom, thereby allowing for more parameter interaction. The modified recession extraction and parameter optimization approaches were tested on three karst springs under different climate conditions. Our results showed that the modified extraction methods are capable of distinguishing different recession components and derived parameters that reasonably represent the analyzed karst systems. We recorded an average Kling–Gupta efficiency KGE > 0.85 among all recession events simulated by the recession parameters derived from all combinations of recession extraction methods and parameter optimization approaches. While there are variabilities among parameters estimated by different combinations of extraction methods, optimization approaches, and seasons, we found much higher variability among individual recession events. We provided suggestions to reduce the uncertainty among individual recession events and raised questions about how to improve confidence in the system's attributes derived from recession parameters.

Testing of The Method of Gama I Synthetic Unit Hydrograph in The Analysis of The Tojo Watershed Design Flood

Floods occur due to several factors including topographic conditions, high rainfall intensity, blockage of water flow, lack of water infiltration areas, deforestation, and so on. The Tojo watershed is included in the Parigi-Poso river area, with an area of 211,830 km2 and a river length of 25.52 km. In the Tojo watershed, it is necessary to study flooding, because the watershed always flows every year. This research aims to find out how much flood discharge was obtained from the analysis of the Tojo watershed design flood with the Gama I synthetic unit hydrograph method and to find out how much the Gama I synthetic unit hydrograph analysis compared to the design flood discharge based on river discharge data (AWLR). From the calculation results obtained a comparison between the design flood discharge value processed by rainfall data using the Gama I Synthetic Unit Hydrograph method to the design flood discharge value processed by the Tojo river discharge data using the log person III distribution method for a 2 year return period is 1957,45 %, for the 5-year return period is 1347,64 %, for the 10 year return period is 1224,65 %, for the 25 year return period is 1169,96 %, for the 50 year return period is 1165,67 % and for the 100 years is 1178,75 %.

Characterization of seasonal groundwater origin and evolution processes in a geologically heterogeneous catchment using geophysical, isotopic and hydro‐chemical techniques (Lough Gur, Ireland)

AbstractLough Gur is a shallow groundwater fed eutrophic lake situated within a small agricultural catchment containing volcanic and karst rock features in mid‐west Ireland. Seasonally active conduits linking two spring discharge locations from the lake under high flow conditions were revealed using dye tracing and a terrestrial geophysical survey, highlighting the architecture of the conduit flow path from Lough Gur to its discharge spring. A radon survey combined with a lake geophysical survey identified the locations of in‐lake discharge springs and thickness of the lakebed sediments. Falling head hydraulic characterization experiments illustrated the heterogenous nature of lakebed sediments and hydrograph analysis coupled with stable isotopes of water (δ18O and δ2H) revealed significant surface water ‐ groundwater interaction during high flow periods. Significantly, δ18O and δ2H signatures plot above the global meteoric water line and local meteoric water line indicating hydration of silicate minerals and direct isotope exchange of δ18O between water and rock minerals. Groundwater δ18O and δ2H signatures during low flow periods indicate that recharge sources are influenced by enriched surface waters and precipitation while a wider range of signatures during high flow periods indicates a greater variation of sources. D‐excess signatures illustrate rapid rainfall infiltration under high flow conditions, thereby demonstrating the vulnerability of the groundwater, while lake water signatures confirm widespread surface water‐groundwater interaction/mixing. Hydrochemical analyses confirm both silicate weathering and carbonate dissolution as primary geochemical processes with Mg/Ca ratios suggesting greater groundwater residence time during low flow periods. Correlations between δ13CDIC and dissolved organic carbon suggest a seasonal switch in the source of DIC to groundwaters between the oxidation of organic matter in summer and dissolution of carbonate minerals in winter. The SI saturation index for calcite (SIC) illustrates calcium carbonate precipitation along with CO2 evasion to be a perennial processes. Finally, the spatial variation for nitrate isotopic signatures (δ18ONO3‐ and δ15NNO3‐) suggests a number of nitrate sources to groundwaters including soil organic nitrogen, manure and/or domestic effluent with indications of denitrification processes under low flow conditions.

Automatic method of flow direction reasoning for bridging tributaries using adjacency relation

AbstractDetermining an accurate flow direction is a prerequisite for hydrographic analysis and river generalization. For river networks with complex spatial structures and little semantic information, it has always been a difficult and interesting problem to automatically and objectively determine the flow direction of all rivers. In a river network with many estuaries, tributaries may either be “simple tributaries” that are associated only with a single main channel or “bridging tributaries” that link multiple main channels. The former is large in number, while the latter is few, but both of them are very important in constructing the hierarchical relationship of the whole river network. Existing studies have concentrated on simple tributaries, and flow direction reasoning for bridging tributaries is ignored, leading to a misunderstanding of the spatial structure of river networks. To address this problem, an automatic method of flow direction reasoning for bridging tributaries using adjacency relation (FDR‐BR method) is proposed. First, in view of the insufficient semantic information in actual river data, the principle of “the minority is subordinate to the majority” is adopted to establish two statistical identification criteria for estuaries, and main channels are extracted by using the good continuity feature between river reaches, that is, stroke feature. Second, the Kth‐order adjacency fields are constructed for each main channel based on the topological connection relationships between the main channels and tributaries. Finally, the “split river reaches” are detected from the bridging tributaries, and the spatial adjacency relation is used as a constraint to identify the benchmark main channel of each bridging tributary. The FDR‐BR method is validated using a geographical census dataset for a city in China. In the experimental area, simple river networks with independent main channels account for 91.67% of the networks, and complex river networks with multiple main channels account for 8.33%. For the complex river networks, 77.79% of the tributaries are simple tributaries, while 13.27% are bridging tributaries. The experimental results reveal that for all rivers in the simple river networks and the simple tributaries in the complex river networks, the flow direction reasoning results of FDR‐BR method are consistent with the results of the state‐of‐the‐art Schwenk method, with an accuracy of more than 98%; for the bridging tributaries in the complex river networks, the flow direction reasoning accuracy of the Schwenk method is only 59.3%, while the accuracy of FDR‐BR method reaches 98%, and the results are more realistic.

Automatic segmentation of parallel drainage patterns supported by a graph convolution neural network

Drainage pattern (DP) recognition is critical in hydrographic analysis, topography identification, and drainage characteristic detection. The traditional method is based on rule computation and self-similarity idea preliminarily performing the DP classification. However, DP segmentation is an uncertain spatial cognitive problem affected by enormous factors. To settle such a multi-conditions decision question, this study takes the segmentation of parallel drainage pattern (SPDP) as an example presenting a deep learning method, namely the graph convolution neural network (GCNN) based on Graph SAmple and aggreGatE (GraphSAGE). First, a directed graph and dual graph were used to construct a dual drainage graph recording spatial-cognition features of drainage. Second, nine drainage features were built to define the graph description from three perspectives: topological connectivity, meandering equilibrium, and directional unity. Finally, the GraphSAGE model was designed for SPDP and trained by typical samples to finish the segmentation works. The experiment examined the optimal feature combination and hyperparameter sensitivity, which can provide sufficient information for SPDP supported by GraphSAGE. Besides, our model outperformed other machine learning methods and GCNNs driven by a fixed quantity sampling mechanism and hydrological knowledge. This work provides a vital reference for hydrology research supported by combing hydrological knowledge with GCNNs.

Joint Modelling of Flood Hydrograph Peak, Volume and Duration Using Copulas—Case Study of Sava and Drava River in Croatia, Europe

Morphodynamic changes in the riverbed may be accelerated by the climate change-induced effects, mostly through the increase of the frequency of extreme climatic events such as floods. This can lead to scouring of the riverbed around the bridge substructure and consequently reduces its overall stability. In order to better understand hydromorphological processes at the local scale, the influence of floods on bridge scour requires a detailed analysis of several interacting flood hydrograph characteristics. This paper presents a multivariate analysis of the annual maximum (AM) flood discharge data at four gauging stations on the Drava and Sava Rivers in Croatia (Europe). As part of the hydrograph analysis, multiple baseflow separation methods were tested. Flood volumes and durations were derived after extracting the baseflow from measured discharge data. Suitable marginal distribution functions were fitted to the peak discharge (Q), flood volume (V) and duration (D) data. Bivariate copula analyses were conducted for the next pairs: peak discharge and volume (Q–V), hydrograph volume and duration (V–D) and peak discharge and hydrograph duration (Q–D). The results of the bivariate copula analyses were used to derive joint return periods for different flood variable combinations, which may serve as a preliminary analysis for the pilot bridges of the R3PEAT project where the aim is to investigate the influences on the riverbed erosion around bridges with installed scour countermeasures. Hence, a design hydrograph was derived that could be used as input data in the hydraulic model for the investigation of the bridge scour dynamics within the project and a preliminary methodology is proposed to be applied. The results indicate that bivariate frequency analysis can be very sensitive to the selected baseflow separation methodology. Therefore, future studies should test multiple baseflow separation methods and visually inspect the performance.

Characterization of basaltic rock aquifer parameters using hydraulic parameters, Theis’s method and aquifer test software in the hard rock area of Buchakewadi watershed Maharashtra, India

The twelve wells were selected to carry out the various test, duration of pumping (min), maximum draw drown (m), duration of recovery (min), residual drawdown, and aquifer type in the basaltic rock aquifer parameters of Buchakewadi watershed. The source and flow of groundwater are essential concerns in hydrological systems that concern both spatially and temporally components of groundwater discharge and water supply problems. The content and temperature of groundwater flowing through an aquifer might change depending on the aquifer environment. As a result, hydrodynamic analyses can provide valuable information about a region's subsurface geology. The present research attempts of aquifer variables such as transmissivity (T) and storativity (S) estimation are significant for groundwater resource development and evaluation. There are numerous approaches for calculating precise aquifer characteristics (i.e., hydrograph analysis, pumping test, etc.). A most frequent in situ analysis is a well-pumping test, which accurately measures the decline and rise of groundwater levels. During an aquifer pumping test, to characterize aquifer properties in an undiscovered location to forecast the rate of depletion of the groundwater table/potentiometric surface. The shallow, weathering subsurface water accessible above the Deccan traps in an unconfined state is insufficient to satisfy the ever-increasing pressure on water supplies. Maharashtra is similarly dominated by hard rocks, whose rainfall susceptibility is limited by weathering and primary porosity, as is their volume to store and convey water. Based on the hydraulic parameters and Theis method, results are optimized. Aquifer mapping and pumping test results can be more important for solving problems such as water scarcity, nonpolluting water, health issues, and source of fresh water on the earth surface. However, the characterization of aquifer parameters should be significant role in the scientific planning and engineering practices.

An Analysis of Hydrographs of the Brahmaputra River at the Gauge Site of Goalpara, Assam

An Analysis of Hydrographs of the Brahmaputra River at the Gauge Site of Goalpara, Assam

Estimation of Groundwater Recharge in the Lobo Catchment (Central-Western Region of Côte d’Ivoire)

Determination of groundwater recharge is a major challenge in areas where rainfall is generally abundant. Variability and uncertainty are inherent in the estimation of recharge, and several methods are therefore recommended for its estimation at a regional level. In this study, we evaluated several methods for estimating recharge: the web GIS-based automated hydrological analysis tool (WHAT), water table fluctuation (WTF), hydrograph analyses, a recession curve displacement method, graphical separation, and empirical formulas. The annual recharge estimated by combining direct recharge and base-flow varied from 84 mm in 2019 to 66.4 mm in 2020. The mean direct recharge was about 44 mm in 2018 and 57.3 mm in 2019, representing about 4% and 5% of the respective rainfall. In 2020, this direct recharge was 43 mm, or about 6% of rainfall, around 25% lower than in 2019. Base-flow separation methods and recession curve displacement generally gave low results, whereas modified empirical formulas gave results close to those of the WTF method and were considered more consistent and reasonable. The regression curve displacement method implemented in the United States geologic survey (USGS) RORA program was found to be unsuitable for the study area. However, the other methods presented more reasonable results and could be used to estimate groundwater recharge in the study area.

Systematic visual analysis of groundwater hydrographs: potential benefits and challenges

Visual analysis of time series in hydrology is frequently seen as a crucial step to becoming acquainted with the nature of the data, as well as detecting unexpected errors, biases, etc. Human eyes, in particular those of a trained expert, are well suited to recognize irregularities and distinct patterns. However, there are limits as to what the eye can resolve and process; moreover, visual analysis is by definition subjective and has low reproducibility. Visual inspection is frequently mentioned in publications, but rarely described in detail, even though it may have significantly affected decisions made in the process of performing the underlying study. This paper presents a visual analysis of groundwater hydrographs that has been performed in relation to attempts to classify groundwater time series as part of developing a new concept for prediction in data-scarce groundwater systems. Within this concept, determining the similarity of groundwater hydrographs is essential. As standard approaches for similarity analysis of groundwater hydrographs do not yet exist, different approaches were developed and tested. This provided the opportunity to carry out a comparison between visual analysis and formal, automated classification approaches. The presented visual classification was carried out on two sets of time series from central Europe and Fennoscandia. It is explained why and where visual classification can be beneficial but also where the limitations and challenges associated with the approach lie. It is concluded that systematic visual analysis of time series in hydrology, despite its subjectivity and low reproducibility, should receive much more attention.

Dynamic Changes in Groundwater Level under Climate Changes in the Gnangara Region, Western Australia

The groundwater-dependent ecosystem in the Gnangara region is confronted with great threats due to the decline in groundwater level since the 1970s. The aim of this study is to apply multiple trend analysis methods at 351 monitoring bores to detect the trends in groundwater level using spatial, temporal and Hydrograph Analysis: Rainfall and Time Trend models, which were applied to evaluate the impacts of rainfall on the groundwater level in the Gnangara region, Western Australia. In the period of 1977–2017, the groundwater level decreased from the Gnangara’s edge to the central-north area, with a maximum trend magnitude of −0.28 m/year. The groundwater level in 1998–2017 exhibited an increasing trend in December–March and a decreasing trend in April–November with the exception of September when compared to 1978–1997. The rainfall + time model based on the cumulative annual residual rainfall technique with a one-month lag during 1990–2017 was determined as the best model. Rainfall had great impacts on the groundwater level in central Gnangara, with the highest impact coefficient being 0.00473, and the impacts reduced gradually from the central area to the boundary region. Other factors such as pine plantation, the topography and landforms, the Tamala Limestone formation, and aquifer groundwater abstraction also had important influences on the groundwater level.

Hydrological Analysis for Water Resources Conservation in the Design of Bandungrejo Lake, Indonesia

An artificial lake design for water resource conservation requires a hydrological analysis that must be comprehensive and detailed to be successful. . This study aims to analyze the maximum rainfall frequency, synthetic unit hydrographs (SUH), design rainfall hyetographs, adequate rainfall, design flood discharge, and lake conservation concepts. The Chi-Square and Kolmogorov-Smirnov tests were used to analyze the maximum rainfall frequency, and the Nakayasu method was used for the Synthetic Unit Hydrograph analysis. The Alternating Block Method (ABM) was employed to analyze the design rainfall hyetograph, and the φ index method was employed for the practical rainfall calculation. The design flood discharge was calculated based on the comparison between the rational method and unit hydrograph. The frequency analysis in average distribution results in 168.7 mm daily rainfall for a 10-year return period, 182.5 mm for a 20-year return period, and 198 mm for a 50-year return period. The Nakayasu analysis shows that the time to peak run-off is 0.56 hours or rounded up to the nearest hour (1st hour). The study of design rainfall hyetograph for a 50-year return period shows 109.0 mm maximum rainfall intensity at the 3rd hour. The adequate rainfall analysis results in 98.5 mm maximum effective rainfall at the 3rd hour. Meanwhile, the Nakayasu method for Synthetic Unit Hydrograph (SUH) obtains 16.68 m3/s design flood discharge for 50 years.

Vertical Mixing and Heat Fluxes Conditioned by a Seismically Imaged Oceanic Front

The southwest Atlantic gyre connects several distinct water masses, which means that this oceanic region is characterized by a complex frontal system and enhanced water mass modification. Despite its significance, the distribution and variability of vertical mixing rates have yet to be determined for this system. Specifically, potential conditioning of mixing rates by frontal structures, in this location and elsewhere, is poorly understood. Here, we analyze vertical seismic (i.e., acoustic) sections from a three-dimensional survey that straddles a major front along the northern portion of the Brazil-Falkland Confluence. Hydrographic analyses constrain the structure and properties of water masses. By spectrally analyzing seismic reflectivity, we calculate spatial and temporal distributions of the dissipation rate of turbulent kinetic energy, ε, of diapycnal mixing rate, K, and of vertical diffusive heat flux, FH. We show that estimates of ε, K, and FH are elevated compared to regional and global mean values. Notably, cross-sectional mean estimates vary little over a 6 week period whilst smaller scale thermohaline structures appear to have a spatially localized effect upon ε, K, and FH. In contrast, a mesoscale front modifies ε and K to a depth of 1 km, across a region of O(100) km. This front clearly enhances mixing rates, both adjacent to its surface outcrop and beneath the mixed layer, whilst also locally suppressing ε and K to a depth of 1 km. As a result, estimates of FH increase by a factor of two in the vicinity of the surface outcrop of the front. Our results yield estimates of ε, K and FH that can be attributed to identifiable thermohaline structures and they show that fronts can play a significant role in water mass modification to depths of 1 km.