Flood is a natural phenomenon that occurs at different intensities and irregular time intervals. As to natural disasters, floods represent the greatest direct threat for the Czech Republic. They may cause serious critical situations during which not only extensive material damages are done, but may bring also losses of the lives of inhabitants in affected areas as well as vast devastation of cultural landscape including environmental damages. Important from the viewpoint of the elimination of potential threats and consequences of such events is the information issued by flood forecasting service about the character and size of flood areas for individual N-year flood discharges and specific flood scenarios. An adequate image of depths and flow rates in the longitudinal or cross profile of the watercourse during a flood event is provided by the hydrodynamic model. This is why the information obtained from the hydrodynamic models occupies a privileged position from the viewpoint of the protection of citizens' lives and mitigation of damage to their property. The first study is situated on the river Úhlava in meadows by Příchovice near the town Přeštice. The proposal of flood-protection measures is contained in Territorial control documentation. The documentation was elaborated on the basis of hydraulic calculations and experiences from the flood in August 2002. The mathematical model is practically used in the study of analysis of proposed flood-protection measures. The analysis is based on mathematical simulation of water outflow and water level on the river Úhlava. It is possible to use the non-commercial software Hec-Ras, version 3.1.1., for the simulation itself. One of the points of view of the possibility of using proposed flood-protection measures is total efficiency. The mathematical model is posssible to use as a basis of support for realization of proposed flood-protection measures on the river Úhlava in meadows by Příchovice within the grant programme "Program prevence před povodněmi II" under the control of the Ministry of Agriculture. In the second case the mathematical model is practically used in the study of hydrotechnical analysis of streams in cadastral unit. The analysis is based on matjematical simulation of water outflow and water level on chosen streams. It is possible to use the noncomercial software HEC-RAS for the own simulation. The analysis should be shown on dangerous places in the interest place. The mathematical model is possible of using to use as basis for revaluation of action in spatial plan or for view of the flood-protection measures in the village Mochtín. Basic input into the hydrodynamic models is represented by altimetry data. One of ways to obtain such data is through the method of aerial laser scanning (ALS) from the digital relief model (DRM). This method is considered one of the most accurate methods for obtaining altimetry data. Its bottleneck is however incapacity of recording terrain geometry under water surface due to the fact that laser beam is absorbed by water mass. The absence of geometric data on watercourse discharge area may perceptibly affect results of modelling, especially if a missing part of the channel represents a significant discharge area with its capacity. One of methods for eliminating the deficiency is a sufficient channel recess by means of software tools such as CroSolver. The third submitted paper deals with the construction of a hydrodynamic model using 5th generation DRM data, and compares outputs from this model at various discharges with a model based on the altimetry data modified by using the CroSolver tool. Outputs from the two hydrodynamic models are compared in HEC-RAS programme with the use of recessed data and with the use of unmodified DRM. The comparison is done on the sections of two watercourses with different terrain morphology and watercourse size. A complementary output is the comparison of inundation areas issuing from both model variants. Our results indicate that differences in the outputs are significant namely in the lower discharges (Q1, Q5) whereas for Q50 and Q100 the difference is negligible with a great role being played by morphology of the modelled area and by the watercourse size.

This study combined flood-frequency analysis, 1-D (one-dimensional) hydraulic modeling using HEC-RAS, and flood-loss modeling using FEMA's Hazus-MH (Hazards U.S. Multi-Hazard) in order to: 1) quantify how different flood-frequency methodologies affect flood-risk assessments, and 2) quantify the impacts of different floodplain-management scenarios along the Middle Mississippi River (MMR). The nine scenarios tested here included various combinations of flood-frequency methodology, buyouts, and levee configurations. The levee configurations analyzed included: 1) current levee configuration, 2) no levees, 3) a 1500 m levee setback, 4) a 1000 m levee setback, and 5) a customized levee setback designed to maximize protection around existing infrastructure. Two study reaches were chosen: (1) an Urban Study Reach within St. Clair and northern Monroe Counties, IL, with levees designed to withstand the 500-year flood and (2) an Agricultural Study Reach within Union and Jackson Counties, IL, with <100-year levees. A flood-frequency analysis was completed for the St. Louis, MO gauging station, and detailed building inventories were used to estimate flood losses on a structure-by-structure basis (Hazus-MH UDF analysis) for an array of floods ranging from the 2- to the 500-year events. These flood-loss estimates were combined with a stochastic levee-failure model. Finally, estimated flood damages from Hazus-MH were integrated across the full range of flood recurrences in order to calculate expected annual damage (EAD). This study's flood-frequency analysis and corresponding flood-loss assessment demonstrate how differences in flood-frequency methodology can significantly impact flood-risk assessments. EAD based on the UMRSFFS (Upper Mississippi River System Flow Frequency Study) flood frequencies was 68% ($45.4 million) lower than EAD based on this study's flood frequencies. This decrease in EAD demonstrates that the UMRSFFS flood frequencies and corresponding stages may significantly underestimate flood risk within the Urban Study Reach. The 100-year discharge in the UMRSFFS appears to be underestimated by an estimated 17% (187,000 cfs), resulting in a 10% (1.6 m) underestimation of the 100-year flood level. Given the magnitude of the EAD, discharge, and stage differences documented here, a reanalysis of the MMR flood frequencies, flood profiles, and flood maps should be considered. The hydraulic modeling completed here showed that levee setbacks and levee removal successfully reduce stages for all recurrence intervals. For the 100-year flood, average reductions ranged from 0.20 m for a 1000 m levee setback to 1.61 m with levees removed. In general, stage reductions increased with increasing discharge and with increasing setback distance. The flood-level reductions are attributed to increased floodwater storage and conveyance across the reconnected floodplain. Compared to the current conditions, the levee setback and levee removal scenarios tested here reduced flood losses for large, infrequent flooding events but increased flood losses for smaller, more frequent flood events. When combined with buyouts of unprotected structures, levee setbacks reduced flood losses for all recurrence intervals. The 1000 m and 1500 m levee setbacks required buyouts in order to reduce EAD; however, a levee setback carefully planned around existing high-value structures reduced EAD with or without buyouts. The planned levee setback configuration combined with buyouts resulted in the largest decreases in EAD: a $16.8 million (55%) decrease in the Urban Study Reach and an $8.3 million (93%) decrease in the Agricultural Study Reach. Overall, this project showed that levee setbacks in combination with buyouts are an economically viable approach for flood-risk reduction along the study reaches and likely elsewhere where levees are widely employed for flood control. Designing a levee setback around existing high-value infrastructure can maximize the benefit of the setback while simultaneously minimizing the costs. Potentially, this type of planned levee configuration could be used as a template for the replacement of aging or failing levee systems.

The present study focuses on the sediment deposition and consequent dredging issues in Lower Ohio River at the Olmsted Locks and Dam area-River mile (RM)-964.4 during the ongoing in-the-wet construction methodology. The study reach is between Locks and Dam 53 (RM 962.6) at upstream, and RM 970 at downstream. One dimensional (1-D) HEC-RAS numerical modeling in conjunction with Arc-GIS was employed. Stream flow measurements, velocity, incoming sediment concentration, bed gradation, and annual hydrographic survey data acquired from public archives of USGS and USACE Louisville District were used as inputs. The model was subjected to the 1-D quasi-unsteady and completely unsteady sediment transport module, available in the latest HEC-RAS 5.0 Beta release. Calibration and validation of the hydrodynamic and sediment models were performed using measured water surface elevation, velocity, and sediment loads at measured sections. Post-model calibration and validation, deposition to excavated cross-sections for future dam shells at Olmsted was predicted, which warrants dredging. The study attempted to analyze the sediment transport trend with the focus on depositionat Olmsted Locks and Dam area using the sensitivity analysis approach of transport capacity functions. Moreover, the capability of 1-D HEC-RAS quasi-unsteady and completely unsteady models were assessed in prediction of sediment deposition in the construction area (dam shells excavation area). A temporal deposition prediction model was developed that can potentially replace the current ad-hoc approach used to determine the dredging schedule. Likewise, a representative environmental risk associated with sedimentation in the study area was examined. The model can potentially be used as a decision support tool to analyze the long term impact of sedimentation in the vicinity of Olmsted Locks and Dam if further updates on the river bathymetry, and specific field data are supplemented to the model.

The Santa Ynez Mountains of Santa Barbara County, California, have seen many major storm events during the past century. San Jose Creek, which runs out of these mountains, through the town of Goleta, and into the Pacific Ocean, has experienced several intense flood events as a result. The lower portion of the creek was diverted in 1960 to alleviate flooding through Old Town Goleta. However, flooding still occurred in the storms of 1995 and 1998. This study incorporates a hydraulic analysis component of a project aimed at re-designing this diverted portion of the channel. It presents an analysis of modifications to this reach in order to improve its capacity and reduce flooding during a 100-year event. As one of the most prominent software for hydraulic modeling for steady and unsteady state open channel flow, HEC-RAS is used to analyze multiple variations in channel geometry and combinations of lining materials. Of these modifications, the best configuration is suggested.

The thesis deals with an evaluation of flood situation at the area of the river Svitava in Brno throughout three different flows Q5, Q20 a Q100 and that proposes a possible solution for flood protection. Current state of the river stream is evaluated through hydraulic calculation combining 1D and 2D numerical modelling of flow rate with the use of HEC-RAS software.

Lake Ringsjön, located in south of Sweden, has been subject of eutrophication since 1950s and received several restoration efforts. Latest restoration effort, “Project Ringsjön”, was proposed in 2003 to improve lake condition against eutrophication by reducing nutrient concentration. This study was done to assess the nutrient loading into the lake from the catchment of Hörbyån Creek, which is discharging into the lake from southeast. Study addresses the nutrient loading conditions from Hörbyån Creek before and after the implementation of “Project Ringsjön” in 1998 and 2010 respectively. Thus a water quality analysis was performed to observe the changes in total nitrogen and total phosphorus concentration in Hörbyån Creek between these years. Effort was also made to investigate nutrients contribution of different watersheds in the catchment. This study also addresses the effect of seasonal variability and land use on nutrient loading. In order to achieve objectives, annual and monthly water quality modelling was performed on the river. HEC-RAS software was used to simulate water quality variables loading from catchment into the lake, such as nitrates, nitrite, ammonium, organic nitrogen, inorganic phosphorus and orthophosphate. Results indicated increase in average annual total nitrogen concentration from 4.18 mg/l to 4.56 mg/l and reduction in average annual total phosphorus concentration from 0.165 mg/l to 0.083 mg/l in the water discharging into the lake from catchment. The watershed occupying mostly agriculture area was observed to have maximum nutrients contribution, which might be due to high fertilizer leakage. It was also observed that maximum nutrient loading was taking place in November and March; probably due to high runoff generated from precipitation and snow melting that carried additional nutrients to the water bodies. Results also indicated that the studied catchment area was contributing high nutrient concentration for eutrophication in both years; however, there was small decrease in total phosphorus concentration in 2010 compare to 1998.

In connection with the government’s approval on the proposed national plan (NAP) in 2019, it has become highly topical to find solutions problems regarding fish migration in Swedish watercourses. At Finsjö Övre hydropower plant in Emån, a new type of fishway is planned to be installed and evaluated starting at the end of 2022. The fishway is a double Archimedes screw turbine that has never been assessed in a Nordic country. The energy company Fortum is operating the power plant. Fortum’s main purpose with the installation is to evaluate the double-screw turbine to gain knowledge about how it performs in Nordic conditions and with Swedish fish species. The evaluation of the fishway will focus on why fish choose to use it or not. It will then be advantageous to have knowledge of velocities in the area below the fishway since fish´s choice of route is affected by that.   The goal of this project was to investigate flow velocities below the intended fishway through hydraulic simulations. Then by the results produce a basis that can be helpful in future evaluations of the fishway’s function for upstream fish migration. In addition to this, to also link the results to previous studies on upstream fish migration to be able to detect shortcomings. In that case to give suggestions for improvement measures.   Field measurements were conducted to collect data on the environment at the hydropower plant. The environment was then recreated in the simulation software HEC-RAS and the planned fishway was added to the model. Three different flow scenarios were assessed and information on flow velocities was obtained.   The simulations showed that the velocity distribution below the fishway probably is suitable for most fish species due to both fast and calm water near the fishway’s opening. No obvious shortcomings emerged. However, the volume flow rate from the fishway is low and is below the recommended guide values. Upstream fish migration will probably work best at low volume flow rates in the river since the velocity of the attraction flow then is relatively high compared to the currents from the hydropower plant. The higher flows from the hydropower plant and the spillway, the less attractive the flow from the fishway becomes. / I samband med att regeringen fattade beslut den nationella planen (NAP) år 2019 har det blivit högaktuellt att hitta lösningar på problematiken kring fiskvandring i svenska vattendrag. Vid Finsjö Övre vattenkraftverk i Emån är en ny sorts fiskväg planerad att installeras och utvärderas med början i slutet av 2022. Fiskvägen är en dubbel Arkimedesskruv som aldrig tidigare har testats i ett nordiskt land. Energiföretaget Fortum, som ansvarar för driften av kraftverket, har som huvudsyfte med installationen att utvärdera skruven för att få kunskap om hur den presterar i nordiska förhållanden och med svenska fiskarter. Vid utvärdering av fiskvägen är det fördelaktigt att ha kunskap om hydrauliska förhållanden i området nedanför fiskvägen, då det bland annat ska undersökas varför fiskar väljer att använda den eller inte.   Målet med detta projekt var att genom hydrauliska simuleringar undersöka flödeshastigheter nedanför den tilltänkta fiskvägen. På så vis sedan ta fram ett underlag som ska kunna användas vid framtida utvärderingar av fiskvägens funktion gällande uppströmsvandring. Utöver detta att också koppla resultaten till tidigare studier kring fiskvandring för att kunna upptäcka eventuella brister och i så fall ge förslag på förbättringsåtgärder.   Fältmätningar genomfördes för att samla in data om miljön vid vattenkraftverket. Därefter återskapades miljön i simuleringsprogrammet HEC-RAS och den planerade fiskvägen adderades till modellen. Tre olika flödesscenarior testades och information om flödeshastigheter erhölls.   Simuleringarna visade att hastighetsfördelningen nedanför fiskvägen troligtvis lämpar sig för flertalet fiskarter på grund av både snabbt och lugnt vatten i nära anslutning till fiskvägens öppning. Inga uppenbara brister visade sig. Dock är flödeshastigheten från fiskvägen låg och ligger under rekommenderade riktvärden. Troligtvis kommer uppströmsvandring fungera bäst vid låga volymflöden i ån eftersom hastigheten på lockvattnet då är relativt hög. För ju högre flöden från kraftverket och spillfåran, desto mindre attraktivt blir flödet från fiskvägen.

Flood plain mapping has become an increasingly important part of flood plain management. Flood plain mapping employs mapping software and hydraulic calculation packages to efficiently map flood plains. Modelers often utilize automation software to develop the complex geometries required to reduce the time to develop hydraulic models. The Utah Inundation Mapping System (UTIMS) is designed to reduce the time required to develop complex geometries for use in flood plain mapping studies. The automated geometries developed by UTIMS include: flood specific river centerlines, bank lines, flow path lines, cross sections and areal averaged n-value polygons. UTIMS thus facilitates developing automated input to US Army Corps of Engineer's HEC-RAS software. Results from HEC-RAS can be imported back to UTIMS for display and mapping. The user can also specify convergence criteria for water surface profile at selected locations along the river and thus run UTIMS and HEC-RAS iteratively till the convergence criterion is met. UTIMS develops a new flood specific geometry file for each iteration, enabling an accurate modeling of flood-plain. Utilizing this robust and easy to operate software within the GIS environment modelers can significantly reduce the time required to develop accurate flood plain maps. The time thus saved in developing the geometries allows modelers to spend more time doing the actual modeling and analyzing results. The time thus saved can also result in faster turn around and potential cost cutting in flood-plain modeling work. In this paper the authors describe UTIMS capabilities, compare them with other available software, and demonstrate the UTIMS flood plain automation process using a case study.

Omställningen till förnyelsebara energikällor innebär att bland annat elproduktionen från vattenkraftverken måste utökas. I Sverige är vattenkraften redan etablerad och platser att bygga nya vattenkraftverk på är få. Därmed är det viktigt att ta vara på de vattenkraftverk som är i drift och om möjligt utöka elproduktionen i de kraftverken. En utökning av elproduktionen i ett vattenkraftverk kan bland annat genomföras genom att rensa och bredda utloppskanalen vilket ökar fallhöjden. Målet för den här studien var att finna den ekonomiskt mest optimala volymen att rensa i utloppskanalen från Rottnens vattenkraftverk för att utöka elproduktionen. Rottnadammen är placerad i anslutning till Rottnens vattenkraftverk och ska eventuellt rivas. En dammrivning medför miljökonsekvenser. Målet från studien var att undersöka vilka miljökonsekvenser en dammrivning medför. För beräkningen av elproduktionseffektiviseringen i Rottnens vattenkraftverk användes programvaran HEC-RAS. HEC-RAS användes för att simulera hur vatten- nivån i utloppskanalen förändras när olika volymer har rensats. För att undersöka miljökonsekvenser av en dammrivning genomfördes en litteraturstudie. Elproduktionsökning i Rottnens vattenkraftverk är möjlig genom rensningar i utloppskanalen i samband med att vattenintaget till Rottneros bruk flyttas från Rottnens vattenkraftverk till sjön Fryken. Det är ekonomiskt mest optimalt att rensa cirka 20 000 m3 vilket medför en elproduktionsökning på ungefär 1,1 GWh/år för ett statistiskt normalår. Inkomsten till följd av elproduktionsökningen är cirka 750 Kkr/år. Investeringskostnaden för en rensning på 20 000 m3 är ungefär 7 300 Kkr. Återbetalningstiden för investeringen är ungefär 16 år. Flytten av vattenintaget innebär att flödet som i dagsläget tas ut från bruket vid Rottnens kraftverk istället kan adderas till flödet som går genom vattenkraftverket och därmed utöka elproduktionen ytterligare. Med det extra flödet skulle elproduktionsökningen i Rottnens vattenkraftverk bli ungefär 1,7 GWh/år för rensning av volymen 20 000 m3 vilket skulle bidra till en inkomst på cirka 1 200 Kkr/år.Resultatet från litteraturstudien visar att det är viktigt att undersöka miljö- konsekvenser av en dammrivning för att kunna göra miljömedvetna val. För en eventuell rivning av Rottnadammen är det viktigt att ta hänsyn till vilken tid på året som rivningen sker för att minimera mängden organiskt material som flödar ut i sjön Fryken. Hastigheten av tömningen är också en viktig faktor för att dammrivningen ska medföra så liten påverkan som möjligt på ekosystemen i och omkring dammen.

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