Silvia Barbetta

River Discharge Estimation by Using Altimetry Data and Simplified Flood Routing Modeling

A methodology to estimate the discharge along rivers, even poorly gauged ones, taking advantage of water level measurements derived from satellite altimetry is proposed. The procedure is based on the application of the Rating Curve Model (RCM), a simple method allowing for the estimation of the flow conditions in a river section using only water levels recorded at that site and the discharges observed at another upstream section. The European Remote-Sensing Satellite 2, ERS-2, and the Environmental Satellite, ENVISAT, altimetry data are used to provide time series of water levels needed for the application of RCM. In order to evaluate the usefulness of the approach, the results are compared with the ones obtained by applying an empirical formula that allows discharge estimation from remotely sensed hydraulic information. To test the proposed procedure, the 236 km-reach of the Po River is investigated, for which five in situ stations and four satellite tracks are available. Results show that RCM is able to appropriately represent the discharge, and its performance is better than the empirical formula, although this latter does not require upstream hydrometric data. Given its simple formal structure, the proposed approach can be conveniently utilized in ungauged sites where only the survey of the cross-section is needed.

Coupling MODIS and Radar Altimetry Data for Discharge Estimation in Poorly Gauged River Basins

The capability of coupling measurements of river velocity derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and water levels derived from ENVISAT Advanced Radar Altimeter (RA-2) for river discharge estimation is thoroughly investigated. The method is applied even considering the possible unavailability of the river cross-section survey by using the entropy theory for reconstructing the bathymetry. The discharge estimation accuracy is validated using in situ measurements along the Po River (Northern Italy) where daily observations are available for the period 2005-2010. The agreement with the observed discharge is fairly satisfactory with coefficient of correlation of 0.91 and relative root-mean-square error (RMSE) of 37 on average. Therefore, the coupling of the two sensors provides, with a good level of accuracy, the hydraulic quantities to use for discharge estimation. These results are particularly significant for the forthcoming European Space Agency Sentinel-3 mission, in which a visible-near infrared multispectral sensor and an altimeter will be onboard the same satellite platform providing significant improvements in terms of vertical accuracy and spatial-temporal resolution.

Case Study: Improving Real-Time Stage Forecasting Muskingum Model by Incorporating the Rating Curve Model

Analysis of forecasts obtained by a forecasting model called STAFOM, a Muskingum-type model for real-time application, shows that the model provides accurate forecast stage estimates for most of the selected case studies and flood events in the Upper-Middle Tiber River basin in central Italy. However, three main issues affected STAFOM: (1) its kinematic nature, (2) the lateral inflows representation, and (3) the occurrence of sudden fluctuations in water levels observed at the ends of the equipped river reach. Therefore, this simple stage forecasting model is hereby improved by incorporating a methodology relating local stage and remote discharge along river channels. This latter procedure, based on the rating curve model (RCM), is capable of reconstructing a discharge hydrograph at a river site where only the stage is monitored, while the discharge is recorded at another section located far away and for which a significant lateral inflow contribution is expected. Application of the new model, named STAFOM-RCM, to several flood events that occurred along four equipped river reaches of the Upper-Middle Tiber River basin, shows that it improves the stage forecast accuracy both in peak and stage hydrograph primarily for long river reaches, thus allowing consideration of a longer forecast lead time; and hence, avoiding the use of the old two-connecting river branch scheme that amplified the fluctuations in observed water levels. DOI: 10.1061/(ASCE)HE.1943-5584.0000345.

A real-time stage Muskingum forecasting model for a site without rating curve

Abstract An adaptive model for on-line stage forecasting is proposed for river reaches where significant lateral inflow contributions occur. The model is based on the Muskingum method and requires the estimation of four parameters if the downstream rating curve is unknown; otherwise only two parameters have to be determined. As the choice of the forecast lead time is linked to wave travel time along the reach, to increase the lead time, a schematization of two connected river reaches is also investigated. The variability of lateral inflow is accounted for through an on-line adaptive procedure. Calibration and validation of the model were carried out by applying it to different flood events observed in two equipped river reaches of the upper-middle Tiber basin in central Italy, characterized by a significant contributing drainage area. Even if the rating curve is unknown at the downstream section, the forecast stage hydrographs were found in good agreement with those observed. Errors in peak stage and time to peak along with the persistence coefficient values show that the model has potential as a practical tool for on-line flood risk management.

Multilinear Muskingum Method for Stage-Hydrograph Routing in Compound Channels

A multilinear stage-hydrograph routing method based on time distribution scheme is analyzed. The framework of the multilinear method is based on the Muskingum-type routing method, which is used as the linear submodel. The proposed method can implicitly model the nonlinear dynamics of the flood wave propagation by varying the model parameters at each routing time step. The suitability of this flood routing method is verified using a set of laboratory experimental data and the field data of the Tiber River in central Italy.

Genetic Algorithm-Based Discharge Estimation at Sites Receiving Lateral Inflows

The genetic algorithm (GA) technique is applied to obtain optimal parameter values of the standard rating curve model (RCM) for predicting, in real time, event-based flow discharge hydrographs at sites receiving significant lateral inflows. The standard RCM uses the information of discharge and effective cross-sectional flow area at an upstream station and effective cross-sectional flow area wave travel time later at a downstream station to predict the flow rate at this last site. The GA technique obtains the optimal parameter values of the model, here defined as the GA-RCM model, by minimizing the mean absolute error objective function. The GA-RCM model was tested to predict hydrographs at three different stations, located on the Upper Tiber River in central Italy. The wave travel times characterizing the three selected river branches are, on the average, 4, 8, and 12 h . For each river reach, seven events were employed, four for the model parameters’ calibration and three for model testing. The GA appro...

Rating Curve Development at Ungauged River Sites using Variable Parameter Muskingum Discharge Routing Method

A physically based simplified discharge routing method, namely, the variable parameter Muskingum discharge-hydrograph (VPMD) routing method, having the capability of estimating the stage hydrographs simultaneously in channels with floodplains is presented herein. The upstream discharge hydrograph is routed using this VPMD method in different two-stage symmetrical trapezoidal compound cross section channel reaches. The performance of the VPMD method is evaluated by numerical experiments using the benchmark MIKE11 hydrodynamic model and the field data of the Tiber River in central Italy. The proposed method is capable of accurately routing the discharge hydrographs, corresponding stage hydrographs and synthesizing the normal rating curves at any downstream ungauged river site which is not affected by any downstream effects. This study can be helpful for various planning and management of river water resources in both the diagnostic and prognostic modes.

ASSESSMENT OF RIVER FLOW WITH SIGNIFICANT LATERAL INFLOW THROUGH REVERSE ROUTING MODELING

The discharge hydrograph estimation in rivers based on reverse routing modeling and using only water level data at two gauged sections is here extended to the most general case of significant lateral flow contribution, without needing to deploy rainfall-runoff procedures. The proposed methodology solves the Saint-Venant equations in diffusive form also involving the lateral contribution using an ‘head driven’ modeling approach where lateral inflow is assumed to be function of the water level at the tributary junction. The procedure allows to assess the discharge hydrograph at ends of a selected river reach with significant lateral inflow, starting from the stage recorded there and without needing rainfall data. Specifically, the MAST 1D hydraulic model is applied to solve the diffusive wave equation using the observed stage hydrograph at the upstream section as upstream boundary condition. The other required data are: 1) the observed stage hydrograph at the downstream section, as benchmark for the parameter calibration, 2) the bathymetry of the river reach, from the upstream section to a short distance after the downstream gauged section. The method is validated with different flood events observed in two river reaches with a significant intermediate basin, where reliable rating curves were available, selected along the Tiber River, in central Italy, and the Alzette River, in Luxembourg. Very good performance indices are found for the computed discharge hydrographs at both the channel ends and along the tributaries. The mean Nash Sutcliffe value (NSq) at the channel ends of two rivers is found equal to 0.99 and 0.86 for the upstream and downstream sites, respectively. The procedure is also validated on a longer stretch of the Tiber River including three tributaries for which appreciable results are obtained in terms of NSq for the computed discharge hydrographs at both the channel ends for three investigated flood events.

Spillway Collapse of the Montedoglio Dam on the Tiber River, Central Italy: Data Collection and Event Analysis

AbstractA large number of dams were built in Italy in the first decades of the last century to supply the needs of industrial, electric power, agricultural, and drinking purposes. Among them, the Montedoglio dam, an important reservoir on the Tiber River located in central Italy, with a drainage area of 276  km2 and a maximum storage volume of about 153  Mm3. The dam is an earth-fill structure with overfall spillway partly controlled by two sluice gates. On December 29, 2010, due to the partial sudden collapse of the spillway, a huge volume of water flooded the valley below the dam, severely damaging the territory, but luckily without causalities. Considering that scarce data are available for this type of event worldwide, this paper aims to illustrate the collected data of the studied event in terms of reservoir levels, using a discharge hydrograph observed at downstream gauged river sites and the flooded valley area. This study aims also to simulate the breach evolution and the downstream propagation of...

A reappraisal of bridge piers scour vulnerability: a case study in the Upper Tiber River basin (central Italy)

The issue of bridge piers vulnerability to scour is addressed by comparing two procedures. The first method quantifies the Scour Vulnerability Index (SVI) considering the combined effects of local and contraction scour. The method requires that a scale factor, for taking account of the scour depth overestimation provided by empirical formulae, is quantified for the selected case study through inspection campaigns. The second approach identifies a vulnerability index to vertical instability depending on several indicators. The study is carried out for a sample of 46 bridges in the Tiber River basin, central Italy, and shows that the two methods identify the same number of piers affected by ‘high’ vulnerability. Results are supplemented by outcomes of inspections that identified, through the scale factor, a high correlation between measured scour depth and SVI value. SVI, simpler and most practical, seems useful for an expeditious estimate of scour vulnerability in large areas and can be adopted by decision makers to identify the structures requiring attention in terms of maintenance and control. The presented results do not provide a general rule for a correct estimate of scour. They refer to solely the investigated case study and need to be verified in other rivers context.