Maximum Reservoir Level Research Articles

Behavior, escapement, and mortality of adult Muskellunge in Midwestern reservoirs

Muskellunge Esox masquinongy is a popular species commonly introduced to warm-water reservoirs; however, little is known about seasonal habitat use and movement in these systems which may result in reservoir escapement and reduced Muskellunge abundance. Our objectives were to assess Muskellunge seasonal behaviors and quantify escapement and natural mortality to determine their effects on populations. Muskellunge captured from the lake and spillway were implanted with radio tags in Big Creek (n = 17) and Brushy Creek (n = 30) lakes, Iowa, USA beginning October 2016 and tracked through May 2019. Telemetry data were used to quantify depth at fish locations, movement rates, annual core and home ranges, and proportions of tagged Muskellunge using spillway approach areas. Telemetry encounter data were analyzed using a multi-state model with water temperature and reservoir water level covariates to estimate escapement and natural mortality. Muskellunge in Brushy Creek were located in deeper water than in Big Creek, but depth and movement were similar across seasons and behavior did not differ between fish captured in-lake and the spillway. Big Creek Muskellunge exhibited greater movements in spring, were located in shallow water and moved less in summer, and were found in deeper water during winter. Core and home ranges were similar between lakes and many tagged Muskellunge frequently used spillway approach areas during spring and summer. No escapement occurred from Big Creek (physical barrier on spillway) while weekly escapement probability from Brushy Creek (no barrier) was up to 0.13 and annual escapement ranged from 18 to 54 %. Escapement was greatest from May-August and increased with increasing weekly maximum reservoir level. Natural mortality was similar between systems, ranged from 15 to 18 % annually, and increased with water temperature. Our results suggest escapement can lead to greater loss of Muskellunge from reservoir populations than natural mortality and may be greater in spring and summer. However, escapement does not appear to be associated with fish behaviors.

Evaluating the Management of a Tropical Reservoir: Implications of Climate Change for Water Availability

Most tropical islands have limited water supply due to the small size of their watersheds and aquifers, unique geology, and distribution of rainfall; each affecting the reliability of water resources for meeting agricultural needs. To improve water supply, reservoirs provide critical storage of surface water. However, climate-driven shifts in the distribution, intensity, and amount of rainfall will alter runoff that feeds reservoirs. Mass-balance modeling was used to evaluate the effects of various management constraints on water availability for the Wahiawā Reservoir (O‘ahu, Hawai‘i) as well as the impact of 20% less dry season rainfall and stream flow to assess the effect of projected climate change on maintaining: (1) a minimum downstream flow; (2) a minimum agricultural supply; (3) a minimum and maximum reservoir level; and (4) a combination of minimum downstream flow and minimum agricultural supply. Under current climate conditions, maintaining a minimal downstream water release could be met with minimal consequences for agricultural supply and reservoir level. However, both agricultural supply and downstream flow had to be reduced during dry periods to keep the reservoir level above a minimum level. Maintaining a minimum downstream flow resulted in a 4.2% reduction in mean agricultural supply and 2.2% reduction in mean reservoir elevation compared to baseline conditions. By contrast, a 20% reduction in dry season water inputs resulted in a 17.8% reduction in mean agricultural supply in the minimum downstream flow scenario compared to current rainfall conditions. Furthermore, the number of days the reservoir level dropped below the minimum needed for a fishery increased (range 1.15–25×) across scenarios compared to baseline. Successful management of surface water within a social-ecological system will be challenged by the increasing unpredictability of rainfall.

Flood Control Versus Water Conservation in Reservoirs: A New Policy to Allocate Available Storage

The aim of this study is to contribute to solving conflicts that arise in the operation of multipurpose reservoirs when determining maximum conservation levels (MCLs). The specification of MCLs in reservoirs that are operated for water supply and flood control may imply a reduction in the volume of water supplied with a pre-defined reliability in the system. The procedure presented in this study consists of the joint optimization of the reservoir yield with a specific reliability subject to constraints imposed by hydrological dam safety and downstream river safety. We analyzed two different scenarios by considering constant or variable initial reservoir level prior to extreme flood events. In order to achieve the global optimum configuration of MCLs for each season, we propose the joint optimization of three variables: minimize the maximum reservoir level (return period of 1000 years), minimize the maximum released outflow (return period of 500 years) and maximize the reservoir yield with 90% reliability. We applied the methodology to Riaño Dam, jointly operated for irrigation and flood control. Improvements in the maximum reservoir yield (with 90% reliability) increased up to 10.1% with respect to the currently supplied annual demand (545 hm3) for the same level of dam and downstream hydrological safety. The improvement could increase up to 26.8% when compared to deterministic procedures. Moreover, dam stakeholders can select from a set of Pareto-optimal configurations depending on if their main emphasis is to maintain/increase the hydrological safety, or rather to maintain/increase the reservoir yield.

Piano Key Weir Hydraulics: Experimental Study of Flow Patterns and Investigation of the Sloped Crest A-Type PKW

Piano Key Weir is a cost-effective and hydraulically performant solution for spillways, considered as a Climate Change adaptation as well. In order to enhance the understanding of the hydraulic behavior of the A-type PKW and to investigate the effects of introducing a crest slope, an experimental study has been performed. This new configuration aims to reduce the discharge capacity at low heads requested in some cases for flood management purposes, while keeping the same maximum reservoir level. In this paper, three models have been tested first in order to investigate the scale effects and the flow patterns in terms of discharge capacity, velocity field and nappe behavior. Then, seven PKW configurations with different crest slopes have been studied. Results confirm the relevant influence of the scale effect at low heads. The comparison of the experimental discharges with the ones predicted by the published analytical formulations, inside their validity fields, shows, a similar trend within ±15% but not identical results. Clinging, leaping, springing and drowned flow regimes ranges have been quantified. The velocity fields have also been analyzed. The results of the sloped crest PKW investigation reveal that the discharge capacity is significantly reduced at low relative heads H/P 0.6 with a maximum deviation of 10%.

FLOOD MODELING OF RIVER GODAVARI USING HEC-RAS

Many cities and towns are developed on downstream side of dams. Some of them are established on the banks of river. During the monsoon period, when the dam is full at its Maximum Reservoir Level (MRL) and still the surplus floods are approaching into dam submergence, the maximum discharge is released from the dam to avoid the overtopping. This results into floods on downstream and may cause the disaster in cities or towns settled on banks of rivers. To facilitate the appropriate measures for effective flood mitigation in advance, there is a need to model the flood plain. With the advent of modern technology, the use of sophisticated softwares in flood modeling helps in getting an idea of extent of flood at its submergence. This paper presents a case study of Godavari river flood modeling using HEC-RAS software. The flood released for Gangapur dam, which is constructed on upstream of Nashik city at 14 km distance is considered for the modeling. The flood discharge is based on the worst discharge of 1969 flood. The river, 14 bridges across the river and the flood plain are modeled. The model facilitates to locate the flood plain and its extent for effective flood mitigation measures.

Assessment of hydraulic load acting on dams including filling variability and stochastic simulations

ABSTRACT Standard practice in dam engineering is to consider only the maximum reservoir level governing the maximum hydraulic loading. This article presents a probability method for modelling reservoir level and the corresponding load on the dam. It uses multiple randomly-generated flood hydrographs to investigate the effect of reservoir level variability. The method was tried on three operational dams to assess its utility as an operational dam safety analysis method.

Modeling the heterogeneous hydraulic properties of faults using constraints from reservoir‐induced seismicity

This research uses observations of reservoir‐induced seismicity beneath Açu Reservoir, NE Brazil, to investigate the spatial distribution of permeability within the damage zone surrounding faults. The Açu dam is a 34 m high earth‐filled dam constructed in 1983 on an area of Precambrian shield. Our previous work has shown that fluctuations in seismic activity are related to varying reservoir level via the diffusion of pore pressure within high‐permeability faults embedded in a lower‐permeability matrix. High‐resolution monitoring of the seismic activity within individual faults, using a network of three‐component digital seismographs, has revealed a complex spatial pattern of earthquake clustering and migration that suggests heterogeneous fault zone hydraulic properties are present. We first review the laboratory and field evidence for variations in hydraulic properties associated with (1) structural architecture of faults and (2) confining pressure. We then model flow through a heterogeneous two‐dimensional (2‐D) fault embedded in, and explicitly coupled to, a 3‐D medium and include a power law decay in diffusivity with depth associated with crack closure. Diffusivity of the fault is represented by a spatially correlated random field. We vary both the correlation length and variance of the diffusivity field and calculate the time lag between the maximum reservoir level and the maximum piezometric head in the depth range of observed seismic activity. By assuming that individual earthquake ruptures occur when the local piezometric head is at a maximum, we are able to infer the correlation length and variance that best explain the spatiotemporal pattern of the activity within each seismic cluster. The spatial and temporal evolution of seismicity within clusters is only found to be consistent with a causal mechanism of pore pressure diffusion when significant spatial structure is present in the heterogeneous fault hydraulic properties.

Numerical modelling of pore-pressure diffusion in a reservoir-induced seismicity site in northeast Brazil

A 3-D fluid-flow model is used to investigate pore-pressure diffusion as a mechanism for reservoir-induced seismicity (RIS) at the Acu reservoir in NE Brazil. The Acu dam is a 34-m high earth-filled dam constructed in 1983 on an area of Precambrian shield. Seismic activity in this area has been monitored over a 10-yr period (1987-1997). The frequency of earthquakes clearly varies with seasonal fluctuations of the reservoir level. Information on the hydrological regime of the Acu reservoir (rainfall, vegetation, surface and subsurface storage, etc.) is used to set up a regional groundwater-flow model in order to obtain boundary conditions for a more detailed study of the area of seismic activity. To explain the observed time lag between maximum reservoir level and peak seismic activity we calculate the magnitude and timing of the maximum piezometric head in the depth range of observed seismic activity. By assuming that individual earthquake ruptures occur when the local piezometric head is at a maximum, values of bulk permeability, K, and storativity, S, are derived. If a 3-D homogenous subsurface permeability structure is assumed then the values of K and S obtained are not self-consistent and are physically unrealistic. However, if a high-permeability fault is embedded into, and explicitly coupled with, the surrounding lower-permeability matrix, then our estimates of subsurface hydraulic properties agree well with other field and laboratory measurements. The inclusion of a discrete fault plane in the model is consistent with the results of high-resolution seismic monitoring using a local digital network of stations, which show that the earthquake hypocentres define a set of steeply dipping NE-striking fault planes beneath the reservoir.

Slope stability of Tehri Dam Reservoir Area, India, using landslide hazard zonation (LHZ) mapping

Abstract A 260 m high dam is under construction across the Bhagirathi River in the Garhwal Himalaya (India) to impound 3.6 x 10 9 m 3 of water at the maximum reservoir level. The reservoir will over a distance of about 44 km in the Bhagirathi Valley and about 25 km in the Bhillangna Valley. A landslide hazard zonation map of the reservoir area has been prepared. The relative influences of six major causative factors have been calculated to identify the important controlling factors in high hazard slope facets.

Flood Storage in Reservoirs

Flood storage in reservoirs controlled by free‐overflowing, rectangular spillways is investigated by accounting for arbitrary reservoir bathymetry and single‐peaked inflow hydrographs. The general solution of the storage equation depends only on a storage factor. It is found that adequate substitution of the effective hydrograph by a model hydrograph has only a secondary effect on the maximum reservoir outflow when using a proper shape factor. The proposed method allows an immediate application to realistic cases. In particular, the maximum reservoir outflow and the corresponding maximum reservoir level are represented graphically. Of further interest are cases in which the spillway crest length is varied for cost optimization purposes. Computations are explained in detail by examples, one of which includes a comparison of the present solution with the result of the numerically integrated basic equation.

Seepage through till foundations of dams of the Eastmain – Opinaca – La Grande diversion

The EOL (Eastmain – Opinaca – La Grande) diversion scheme of the La Grande Complex (phase I) for the James Bay Hydroelectric development in northern Québec diverts the waters of the Eastmain, Opinaca, and Petite Opinaca Rivers into the LG 2 reservoir. The EOL diversion consists of four dams and seven dykes about half of which are founded for part of their length on overburden foundations of variable thickness and consisting of heterogeneous deposits of glacial till or sandy and silty alluvia. The till core of these zoned embankments is either placed directly on the till strata or extended through the alluvia to the underlying till by a core trench. The construction of these embankments was completed in 1979 and the maximum reservoir level achieved in November 1980.This paper deals with the seepage and pore pressure behaviour in the overburden foundations, namely, dams OA-10B and OA-11 and the dyke OA-8B, during and subsequent to the reservoir filling. The results of the parametric seepage analyses carried out by finite element methods are compared with the observations. Special attempts are made to resolve the long-existing speculations regarding the anisotropy of natural deposits. Comments are made regarding the effective anisotropy of such deposits in the James Bay region and its effect on exit gradients and uplift forces, which influence the design and safety of dams and dykes. Keywords: seepage, pore pressure, hydraulic conductivity, anisotropy, foundation treatment, cutoff.