Hydrological Observation Network Research Articles

DETERMINATION OF THE OPTIMAL OBSERVATION NETWORK FOR HYDROLOGICAL STUDIES OF RIVERS OF ARMENIA

Hydrological observation stations are the source of accurate information necessary for the study of spatiotemporal changes of the river flow and for organizing the effective management of water resources. The paper presents the optimal observation network for hydrological studies of river flow in Armenia. The study is based on the optimization methodology of the regime hydrological observation network developed by I.F.Karasev. Statistical, interpolation, comparison, and analogy methods were used. It was inferred that the optimal observation network for hydrological studies of river flow in Armenia will consist of 86 hydrological observation stations.

Observation of a rapid lake‐drainage event in the Arctic: Set‐up and trigger mechanisms, outburst flood behaviour, and broader fluvial impacts

AbstractLakes set in arctic permafrost landscapes can be susceptible to rapid drainage and downstream flood generation. Of many thousands of lakes in northern Alaska, hundreds have been identified as having high drainage potential directly to river systems and 18 such drainage events have been documented since 1955. In 2018 we began monitoring a large lake with high drainage potential as part of a long‐term hydrological observation network designed to evaluate impacts of land use and climate change. In early June 2022, surface water was observed flowing over a 30‐m wide bluff, with active headward erosion of ice‐rich permafrost soils apparent by late June. This overflow point breached rapidly in early July, draining almost the entire lake within 12 h and generating a 191 m3/s flood to a downstream creek. Water level and turbidity sensors and time‐lapse cameras captured this rapid lake‐drainage event at high resolution. A wind‐driven surface seiche and warming waters following ice‐out helped trigger the initial thermomechanical breach. We estimate at least 600 MT of lake sediment was eroded, mobilized, and transported downstream. A flood wave peaking at 42 m3/s arrived 14 h after the initial breach at a river gauge 9‐km downstream. Comparing this event with three other quantified arctic lake‐drainage floods suggests that lake surface area coupled with drainage gradient height can predict outburst flood magnitude. Using this relationship we estimated future flood hazards from the 146 lakes in the Arctic Coastal Plain of northern Alaska (ACP) with high drainage potential, of which 20% are expected to generate outburst floods exceeding 100 m3/s to downstream rivers. This fortunate and detailed drainage‐event observation adds to a growing body of research on the impact of lakes on arctic hydrology, hazard forecasting in a region with an increasing human footprint, and broader processes of landscape evolution in arctic lowlands.

DOPPLER NON-CONTACT RADAR SENSORS FOR WATER DISCHARGE ESTIMATION: ADVANTAGES AND LIMITATIONS

The use of non-contact doppler flow radars to determine water discharge is a widespread trend in hydrometeorological surveying and monitoring. However, is it reasonable to consider such an instrument as one of the most suitable and perspective for the hydrological observation network? In-situ testing have been carrying out by authors of this article and the analysis performed in scientific papers cannot provide a single-valued positive conclusion on this issue. Obvious advantage of these radars as independent safe mode of operation seems to overweight their obvious weak points. Many "undercurrents" do not allow this method to be recognized as reliable, such as the problem of transition from surface to medium flow velocities, which consists in the data processing apparatus, reliable positioning of the device, blanking distance task and etc. All in all, this article discusses the main advantages and "vulnerabilities" of the use of such an instrument as non-contact doppler radars to determine water discharge from a scientific and practical points of view.

ОЦІНКА ПРОСТОРОВИХ ВЗАЄМОЗВ’ЯЗКІВ СЕРЕДНЬОГО РІЧНОГО СТОКУ ВОДИ РІЧОК В МЕЖАХ ПРАВОБЕРЕЖЖЯ ПРИП’ЯТІ

Assessment of the spatial relationships of any element of river water flow or meteorological indicators of a certain territory is based on the use of the spatial correlation function. The aim of the presented study is to construct such a function for the average annual water flow of the rivers of the right-bank part of the Pripyat basin and to establish the territorial patterns of its interrelations. The initial data were the series of observations of the average annual water discharges on 11 rivers, which turned out to be representative for further calculations. Checking the series of observations for homogeneity was carried out according to the parametric criteria: t -Student’s and F-Fisher’s at the 5% and 1% significance levels. She showed that the rows are uniform. Only a sequence of average annual water discharges on the river Pripyat near the village of Rechitsa turned out to be heterogeneous according to Fisher’s criterion. Based on the calculations, two matrices were obtained – the correlation matrix of the average annual river water flow and the matrix of distances between the centers of attraction of their basins, on the basis of which the spatial correlation function r = f (L) of the average annual river water flow for the territory of Pripyat within Ukraine was constructed. The largest number of joint years of observations in determining the correlation coefficients was 70 years, the smallest – 52. The resulting regression equation of the spatial correlation function was evaluated for accuracy and homogeneity. This test gave positive results. It was found that the pair correlation coefficients decrease with an increase in the distance between the centers of river basins. Significant spatial relationships of the average annual river flow for the territory of Pripyat within Ukraine with correlation coefficients of more than 0.75 are observed at a distance of up to 100 km between them. Satisfactory territorial correlation with a coefficient ranging from 0.60 to 0.75 – at a distance between them up to 100-150 km. The development can be used for practical purposes in hydrological calculations and forecasts, to optimize the hydrological observation network, etc.

Intergovernmental cooperation for hydrometry – what, why and how?

ABSTRACT Two thirds of hydrological observation networks in developing countries are reported to be in poor or declining condition. At the same time innovation in sensor technologies and data processing are presenting opportunities for enhancing observation networks that are not being realized. The World Meteorological Organization’s Global Hydrometry Support Facility, or WMO HydroHub, was launched in 2016 to transform assistance to operational water monitoring agencies around the world. If successful, the initiative will increase the amount of hydrometric data available to researchers, catchment managers and water policy makers. To those unfamiliar with UN organizations, however, the nature of such initiatives, the reasoning behind the decisions taken to establish them and the mechanisms by which they try to deliver benefits for society, can be opaque. This paper adopts a novel dialogue-style format to explore the set-up of the WMO HydroHub and build awareness amongst those who ultimately may benefit from its approaches.

ВИКОРИСТАННЯ РЕГІОНАЛЬНОЇ МОДЕЛІ КЛІМАТУ (REMO) ДЛЯ ОЦІНЮВАННЯ ТЕНДЕНЦІЙ КОЛИВАНЬ СТОКУ ВОДИ В БАСЕЙНІ ДНІСТРА

In order to confirm the possibility of predictive climate models using for the flow modelling in the Dniester river basin, the REMO climate model was verified. The verification was carried out on the basis of comparison of the simulated values and data from the hydrological observation network. The data of 28 hydrological stations on the Dniester and its tributaries were used. The reference period for testing the model was from 1971 to 2000. In total, 11 136 values of the average monthly and 917 values of the average annual water flow were used. According to the results of the conducted research, it was found that in most cases, the average annual flow value, taken from the model REMO, is lower, compared with the data from the hydrological observation network. The mean annual flow in the Dniester basin according to the hydrological observation network is 9.25 l/s∙km2, based on the model REMO – 8.27 l/s∙km2. In order to reduce the deviations of the predicted values, it was proposed to use a correction factor, it can reduce the percentage of deviations from the measured values by half. The assessment of the relationship between the data from the hydrological observation network and model values was carried out on the basis of determining the coefficient of pair correlation with the subsequent calculation of the regression equation. It was found that the correlation coefficient for a pair of data of the average long-term value – measured and model – is close to 1, which confirms the possibility of modelling not only for certain designated areas but also for individual hydrological stations. This research shows that the model REMO reliably predicts water flow changes in the Dniester river basin, taking into account the peculiarities of flow formation in different parts of the studied basin.

Hydrological predictions for small ungauged watersheds in the Sudanian zone of the Volta basin in West Africa

Abstract Study region Hydrological observation networks in the West African region are not dense and reliable. Furthermore, the few available discharge data often present significant gaps. The Volta basin, the second largest transboundary basin in the region, is a typical example of a basin with inadequate hydrological networks. Study focus In this study, a prediction approach to determine monthly discharge in ungauged watersheds is developed. The approach is based on the calibration of two conceptual models for gauged watersheds and an estimation of models’ parameters from the physical and climatic characteristics of the watersheds. The models’ parameters were determined for each ungauged watershed through two different methods: the multiple linear regressions and the kriging method. The two methods were first validated on five gauged watersheds and then applied to the three ungauged watersheds. New hydrological insights for the region The application of the two hydrological models on the eight watersheds helped to produce relevant monthly runoff and to establish the annual hydrological balances from 1970 to 2000 for both gauged and ungauged watersheds. The developed method in this study could therefore help estimate runoff time series, which are of crucial importance when it comes to design hydraulic structures such as small reservoirs.

Development and performance analysis of satellite communication system for real-time river monitoring

K-water uses its Koreasat No. 5-based communications network for remote acquisition and provision of hydrological information on rainfall, water levels, water quality, and warnings via its hydrological observation network. The satellite is greatly affected by the rainfall attenuation during heavy rainfall seasons and typhoons since it is using the Ku-band frequency. K-water used the site diversity (SD) technology and developed a duplexing system that involved the setup of its main hub station at its headquarters and its auxiliary hub station at Gunnam Dam located at 200 km away, to smoothly use its data during rainfall attenuation and satellite malfunctions. In this paper, we proposed an online monitoring SD system in the communications satellite equipment and manual/automatic switching algorithms. We examined the SD effects in the projected site to improve the stability and reliability of K-water’s hydrological communications satellite. Data reliability was found to be improved to 96.7% through the comparative study of the existing and SD systems, in which present data observation failure occurred in all 418 terminal stations, but proposed method occurred only in 14 terminals.

Radar Altimetry Aids Managing Gauge Networks

The hydrological observation network in the Amazon basin is made of conventional rainfall and water level stations presently maintained by the Agencia Nacional de Aguas (ANA), the National Agency for Waters. The water level network has long been plagued by difficulties associated with spatial coverage, timely delivery and data errors. Satellite observations are important means for providing hydrologic data with acceptable spatial and temporal resolution, and radar altimeters embarked onboard successive satellites since the early 1970s collect measurements of water level over rivers in a well-defined geodetic reference frame and can be used to address some of these problems. Nowadays, satellite altimetry can be used to collect the time variations of the water levels over many rivers throughout the word, as long as the reach are several hundred meters wide. This ability is particularly interesting in ungauge basins but it can also be used as an independent source of information to cross-check existing gauge series. In the present study, we focus on examples from the Amazon basin where radar altimetry has been used to provide an independent dataset that can be used to support the management of hydrological observation networks by including new data together with conventional field data,

Distribution of hydrological observation network on the rivers of Russia before and after the economic reforms depending on the degree of territorial development

Studied is the relationship between the density of hydrological stations (HS) of the main state observation network on the rivers and the population density commonly used as an indicator of the territory development. Given is the minimal required number of HSs of the main network computed using the objectively substantiated method. The territorial distribution of HS density depending on the population density is analyzed on the basis of the data of 1992 with the number of HSs of the total network that can be taken as minimal required for the main network. For the first time obtained are the regional relations of these characteristics for the time moment when the spatial distribution of HS density was close to the year 1987 to the countrywide highest HS density for the whole observation period. Established is the relationship between the HS density and density of population aggregates.

Reducing uncertainty in estimates of frequency distribution parameters using composite likelihood approach and copula‐based bivariate distributions

Conventional multivariate hydrological frequency analysis utilizes only the concurrent parts of data sets, leaving a lot of nonconcurrent data unutilized. Simultaneous inclusion of such nonconcurrent data can significantly reduce uncertainty in hydrologic design estimates. The methodology proposed in this paper allows varied length multivariate data to be combined and analyzed in an integrated framework through a “Composite Likelihood Approach.” The method employs copula‐based multivariate distributions in order to provide necessary flexibility of admitting arbitrary marginals. The paper presents the theoretical basis of the approach and highlights its advantages through two applications. A significant reduction in uncertainty in design flood quantiles of a relatively shorter flood series is achieved by utilizing an associated downstream flood data. The advantage of the methodology is further demonstrated by establishing significant information gain for six different combinations of Gaussian and non‐Gaussian marginals. The proposed approach marks a paradigm shift in hydrologic design procedures, particularly for partially gauged basins, wherein a higher precision in hydrologic designs is achieved by leveraging associated information that has hitherto remained unutilized. It is opined that the approach will enable offsetting the impact of dwindling hydrological observation networks around the world by enhancing information that is derivable from existing networks.

Hydrological observation and modelling relationship for the determination of water budget in Lusatian post-mining landscape

The hydrological observation network in a small, sparsely vegetated watershed within the post-mining landscape includes measurements of meteorological quantities (precipitation, temperature, global radiation, humidity, wind speed), of water level in a swale by pressure transducers, and of soil water by TDR-probes, tensiometers and a seepage gravity lysimeter. The field observations resulted in a modelling concept, where modules for actual evapotranspiration, soil water movement and surface runoff were specified and coupled with each other. The results of measurements and modelling for a 2 years observation period revealed a predominant relation of the distribution of hydraulic properties on hummocks and erosion channels, formed by runoff and erosion. On hummocks both processes are intensified by the water repellency of the tertiary sandy overburden, which seems to be related to wetting–drying-cycles of the dump substrate. During periods of hydrophobic conditions, surface runoff is increased from the hummocks and most groundwater recharge occurs within the erosion channels. Under consideration of the wetting–drying-cycles, the components of the water balance were obtained from daily precipitation values by a simplified storage approach version of the model in acceptable quality compared to the results of the detailed model version. In this version surface runoff occurs only under water repellent substrate conditions. To analyse the variability of water balance components for a real fluctuation of weather conditions, a 30-year meteorological record was considered. The precipitation in the investigated catchment (corrected for errors of wind, for wetting of the collector and for loss of evaporation from the collector) of 628 mm per year is divided into the evapotranspiration of 325 mm per year, groundwater recharge of 303 mm per year for 30-year average climatic conditions.

Spatial patterns of decline in Pan-Arctic hydrological observation networks: Adaptation to climate change impacts

Spatial patterns of decline in Pan-Arctic hydrological observation networks: Adaptation to climate change impacts

Spatial patterns of decline in Pan-Arctic hydrological observation networks: Adaptation to climate change impacts

This article was submitted without an abstract, please refer to the full-text PDF file.

Water resources for sustainable development

The significance of water availability for sustainable development is discussed. A review of water-related areas of concern in Agenda 21, the blueprint for sustainability, is offered, with particular reference to its Chapter 18 devoted to freshwater resources. The problems of water resources of vulnerable areas are tackled for the examples of arid and semiarid lands, mountains and small islands. The importance of water resources assessment and its building block, hydrological observations, for sustainable development is demonstrated and the adverse tendencies of declining hydrological observation networks are reported. Hydrological network density is seen as one of the indicators of sustainable development. Hydrological and water resources systems are perceived only as a component of the complex global system. Therefore a holistic perspective is advocated, looking at the existing interrelationships and interfaces with other sub-systems, including social, economic, institutional, etc.