Auxiliary Spillway Research Articles

Water management strategies for desirable IWRM implementation and application to the initiative projects, Korea

K-water has led national policymaking in South Korea through a master plan established in 2015 to raise national awareness on integrated water resources management (IWRM). It has promoted leading pilot projects as a short-term plan. Since the construction of the initial dam on the Seomjin River in 1928, inefficient water management has persisted. There was a jumble of agreements, treaties, regulations, and various institutions that could not keep up with the changing conditions in dam operation and water use caused by the construction of the new dam and auxiliary spillways on the river. Also, there were four agencies designated as dam usage rightholders: Two more were added to the original two dam licensees. Accordingly, the initiative project established a consensus on the need to streamline dam operations and promoted deriving social agreements through a council composed of the field-level departments of each water management agency. After government mediation, dam management regulations were revised to determine adjustments in the dam usage rights and the basic priorities in water use. This IWRM pilot model, which promotes the rational use of a dam by multiple users, successfully satisfied each stakeholder’s agreed-upon rights in 2019, the first project year.

Mote Park lake – the planning and design of upgrade works

Mote Park lake, located in Maidstone, Kent, was constructed in its current form in the 1830s. It is situated within a grade 2 listed park. The works set out in the original scope were limited to increasing the capacity of the existing dam spillway. They included construction of an auxiliary spillway to accommodate an extreme flood. During design development, the poor condition of the drawdown facilities was identified. Refurbishment and upgrade to automatic control and operation was included within the scope of works at little additional cost reducing the scope of temporary works required for construction. This paper explains the project background and the reasons for the upgrade to the reservoir, which include the spillway improvements and associated works, refurbishment and upgrade of the drawdown facility, and landscaping and mitigation works required due to its sensitive setting.

An Automated Screening Technique to Identify At-Risk Auxiliary Spillways: Modified Approach in WinDAM

AbstractDam operators often do not know whether an auxiliary spillway will fail until it is loaded, which can be infrequent. Such failures have the potential to result in overall dam failure, leadi...

Toddbrook: the independent government review a forensic approach to causality

The Toddbrook embankment dam was constructed in 1840. A concrete auxiliary spillway chute was added to its crest and downstream slope 50 years ago in 1970. On the 31 July 2019 the auxiliary spillway discharged a significant flood. The following day, as flows died down, the chute progressively collapsed. The author was the all reservoirs panel engineer and member of the independent governmental review team, charged with establishing the cause. The paper describes the forensic approach adopted and how that identified the immediate causal mechanism to be the injection of large quantities of water through cracks on the chute due to flows impacting rocks embedded on the chute invert and developing stagnation pressures. It also concluded that many factors such as poor design, deterioration, poor maintenance and some aspects of poor construction, all probably contributed to weakness in the chute which facilitated crack development.

Toddbrook Reservoir cut-off trench site observations

Significant damage to the auxiliary spillway at Toddbrook Reservoir resulted in the evacuation of 1500 residents from Whaley Bridge for a period of 7 days. During this period, emergency works were carried out to minimise the risk of the embankment failing and allow residents to return to their homes and livelihoods. Since the emergency works, the Canal & River Trust have completed an interim project which includes a number of measures to improve the resilience of the reservoir until the spillway is replaced. This paper presents the site observations made during the construction of the in situ concrete cut-off trench located along the crest of the auxiliary spillway.

Toddbrook: After the Incident

On 1st August 2019, Toddbrook reservoir became, overnight, the most photographed UK reservoir for the last decade. After a series of sequential flood events led to localised failure of a section of the 1970s concrete auxiliary spillway, which passes spill flows over the face of the dam, residents were evacuated from the downstream town of Whaley Bridge due to fears of dam collapse. A multi-agency response was launched, with experts working around the clock to drop the reservoir level and allow residents to return home. The news crews have now moved on and the reservoir sits nearly empty, in wait of a new spillway. Modelling and design work has continued behind the scenes to allow a detailed understanding of the response of the reservoir basin to a range of storm events. A comprehensive water level control plan has been developed, and associated temporary works installed on site, to allow the reservoir to be safely managed in its transitory state. This paper details the ‘make safe’ works installed after the incident, and the ongoing design work to bring the reservoir back into operation and ensure its future resilience.

Toddbrook Reservoir: a case study quantifying the importance of maintaining bywashes

Ongoing maintenance and upkeep of bywashes can be expensive and difficult to justify, particularly in the context of other maintenance costs; in many cases made even more difficult as the structures are only rarely, if ever used. Using experience from the widely reported incident at Toddbrook Reservoir in August 2019 can help to quantify the benefit that bywash structures provide. A hydraulic model was developed to analyse the impact of the bywash in detail. Simulating the passage of the storm of August 2019, this paper demonstrates that the bywash reduced the duration of overtopping the auxiliary spillway by 40 hours (33%), compared to not having it in place. This is likely to have reduced the risk of even more widespread damage to the structure. For the ongoing management of the reservoir, the modelling showed the bywash can pass 2.5 m3/s, which provides the undertaker with operational cost savings (principally from pumping) to maintain the current drawdown. This paper provides an examination of the benefits of an operational bywash during a significant incident. The hydraulic modelling approach adopted has provided a unique opportunity to quantify and demonstrate the benefit for undertakers of maintaining their bywash assets.

Dam-Breach hydrology of the Johnstown flood of 1889-challenging the findings of the 1891 investigation report.

In 1891 a report was published by an ASCE committee to investigate the cause of the Johnstown flood of 1889. They concluded that changes made to the dam by the South Fork Fishing and Hunting Club did not cause the disaster because the embankment would have been overflowed and breached if the changes were not made. We dispute that conclusion based on hydraulic analyses of the dam as originally built, estimates of the time of concentration and time to peak for the South Fork drainage basin, and reported conditions at the dam and in the watershed.We present a LiDAR-based volume of Lake Conemaugh at the time of dam failure (1.455 × 107 m3) and hydrographs of flood discharge and lake stage decline. Our analytical approach incorporates the complex shape of this dam breach. More than 65 min would have been needed to drain most of the lake, not the 45 min cited by most sources. Peak flood discharges were likely in the range 7200 to 8970 m3 s−1. The original dam design, with a crest ∼0.9 m higher and the added capacity of an auxiliary spillway and five discharge pipes, had a discharge capacity at overtopping more than twice that of the reconstructed dam. A properly rebuilt dam would not have overtopped and would likely have survived the runoff event, thereby saving thousands of lives.We believe the ASCE report represented state-of-the-art for 1891. However, the report contains discrepancies and lapses in key observations, and relied on excessive reservoir inflow estimates. The confidence they expressed that dam failure was inevitable was inconsistent with information available to the committee. Hydrodynamic erosion was a likely culprit in the 1862 dam failure that seriously damaged the embankment. The Club’s substandard repair of this earlier breach sowed the seeds of its eventual destruction.

Revisiting the Timing and Events Leading to and Causing the Johnstown Flood of 1889

The Johnstown Flood of May 31, 1889, was responsible for more recorded deaths than any other disaster in the United States until the Galveston hurricane of 1900.1 An important difference between the two is that the Johnstown flood was not a natural disaster. Although the Johnstown region was in the midst of a particularly wet spring and the former boroughs that now form the city of Johnstown were already experiencing low-level flood-ing on May 31, the ultimate reason for the high death toll was the catastrophic failure of the South Fork Dam, located fourteen miles upstream from the outskirts of Johnstown on the South Fork of the Little Conemaugh River (see fig. 1). The millions of tons of water released by the failure of the dam caused devastation along the Little Conemaugh River drainage. As the water moved downstream it was temporarily impounded by debris dams behind two Pennsylvania Railroad bridges (Viaduct and Bridge no. 6), which caused "reformation of the lake" at these points. When Bridge no. 6 failed, the rejuvenated flood wave sped toward Johnstown. Most structures

Converging Stepped Spillways: Simplified Momentum Analysis Approach

AbstractRoller compacted concrete (RCC) stepped spillways are growing in popularity for providing overtopping protection for aging watershed dams with inadequate auxiliary spillway capacity and for the construction of new dams. Site conditions, such as limited right-of-way, topography, and geological formations, often dictate that these spillways converge. Convergence increases the flow depth near the training walls and alters the stilling basin design requirements as compared with traditional straight spillways. A simplified control volume momentum analysis is presented for predicting the minimum vertical training wall height necessary to prevent wall overtopping in converging stepped spillways. An expression is developed to predict vertical training wall height as a function of centerline flow depth, centerline velocity, chute slope, and convergence angle. A three-dimensional 3(H):1(V) sloping stepped spillway model with an ogee crest and convergence ranging from 0–70° was constructed to verify this rel...

<p class="HeadingRunIn"><strong>Life history and larval density of <em>Cheumatopsyche digitata</em> Mosely (Trichoptera: Hydropsychidae) in Opa Reservoir spillway, Ile-Ife, southwestern Nigeria</strong></p>

The life history and density of Cheumatopsyche digitata Mosely (Trichoptera: Hydropsychidae) were examined below Opa Reservoir in Ile-Ife, southwestern Nigeria. This caddisfly is the only species that occurs immediately below the impoundment auxiliary spillway where it closely associates with an aquatic bryophyte, Fontinalis sp. We collected larvae every month between July 2004 and June 2005 as long as larvae were available in the study site. The instar growth ratio was fairly constant and ranged from 1.198 to 1.402 (mean ± standard error = 1.285 ± 0.073) but mean head capsule width increased with larval development. The frequency distribution of head capsule width of larvae clustered into 5 size classes, suggesting 5 larval instars for C. digitata in the study site. Density of larvae ranged from 1,100 to 11,150 inds.m-2 (mean ± SE = 6739 inds.m-2 ± 3904.70), the highest densities occurring in October 2004 during the bloom of Fontinalis. The first larval instar appeared in July 2004. Adult emergence occurred mainly in December 2004 through January 2005 at the onset of reservoir draw-down and death of Fontinalis. These patterns indicate that C. digitata tended to show a univoltine life cycle in the study site.

Numerical Modeling of Probable Maximum Flood Flowing through a System of Spillways

The results of a numerical model study of probable maximum flood (PMF) flow through a system of spillways consisting of an existing service spillway and a new auxiliary spillway are presented. A commercial computational fluid dynamics (CFD) code, Fluent, was used to solve the time-dependent Reynolds-averaged Navier-Stokes equations, a standard turbulence k-ε model with wall functions, and a water volume of fluid fraction equation. A two-dimensional approach velocity profile was used at the upstream inlet cross section. Water levels, flow splits between the existing and auxiliary spillways, and flow patterns were predicted and compared. A tentative design was chosen, constructed, and tested in a 1:54 scale physical model. Testing results were used to validate the CFD model. Results demonstrate that the CFD model is validated as accurate in the prediction of water levels in the reservoir, the integrated approach used is cost-effective and efficient in optimizing the designs of the auxiliary spillway, the tentative design cannot pass the PMF at the maximum pool level which suggests further modifications being necessary in the physical model.

Energy Dissipation on Flat-Sloped Stepped Spillways: Part 1. Upstream of the Inception Point

In recent years, hazard classifications for many existing embankment dams have changed because hydrologic conditions have been altered. Consequently, many of these dams no longer provide adequate spillway capacity according to state and federal dam safety regulations. Stepped spillways are a popular choice for providing increased spillway capacities to existing embankment dams. Stepped spillways in these applications are typically placed over the existing embankment or auxiliary spillway; thereby, the chute slope is the same as the downstream embankment face or auxiliary spillway slope. Design guidelines and literature in general for these stepped spillways are very limited, so further research on these stepped spillways is warranted. A two-dimensional, physical model was constructed to evaluate the inception point, velocities, and energy dissipation in a 4(H):1(V) spillway chute having 38 mm (1.5 in.) high steps. Model unit discharges ranging from 0.11 m3 s-1 m-1 (1.2 cfs ft-1) to 0.82 m3 s-1 m-1 (8.8 cfs ft-1) were tested. Water surfaces, bed surfaces, and velocities were collected during the tests. An inception point relationship provided by H. Chanson may be used to determine the inception point for slopes as flat as 4(H):1(V) when F* ranges between 10 and 100. The velocity profiles transition from uniform at the crest to approaching a one-sixth power law distribution at the inception point for all tested flows. Energy losses increase in a linear fashion from near zero at the crest to approximately 30% near the inception point for all tested flows. This research will assist engineers with the design of stepped spillways applied on relatively flat embankment dams.

The Influence of Soil Moisture and Compaction on Spillway Erosion

Submerged jet tests were conducted on a soil material compacted by dynamic and static load methods over a range of dry unit weights and moisture contents. The compacted soil samples were pre-wet prior to testing. An index parameter was used to compare changes in the erosion resistance of the soil at different compacted dry unit weights and compacted moisture contents. Moisture content at the time of compaction had a significant influence on soil erosion resistance. Additionally, at a constant moisture content, the erosion resistance increased as the dry unit weight increased. These results, along with results of two compacted spillway channel tests on the same soil, suggest that proper compaction should be considered in the repair of earthen auxiliary spillways.

Mechanics of an Earth Spillway Failure

ABSTRACT Severe storms in Mississippi during May of 1983 produced flooding that resulted in one of the few flood control reservoir auxiliary spillway failures on record. Subsequent analysis of the breach using state of the art procedures reproduced the downstream observations of high water, but failed to reproduce the observed timing of the failure or conditions observed at the site during spillway operation and failure. The present effort uses the observed failure conditions, site geology, and a simplified model of failure mechanics to develop an independent estimate of the breach outflow hydrograph. Agreement with the previously estimated peak discharge is surprisingly good. The analysis, although site specific, clearly demonstrates the important role of surface and soil discontinuities in the failure process.

Tarbela Dam Project, Pakistan

The Tarbela Dam Project, now under construction, is a component of the Indus Basin Project, a by-product of the Indus Waters Treaty of 1960 between Pakistan and India. The main embankment dam will close the Indus valley where the river emerges from the Himalayan foothills. Associated with the dam are, on the left bank, two auxiliary dams required to close a side valley and a saddle, and service and auxiliary spillways. On the right bank are four irrigation and power tunnels, water through three of which will drive the 12 units ultimately to be installed in a powerhouse just downstream of the dam. The reservoir will provide 9.3 MAF of live irrigation storage; the powerhouse will contain 2,100,000 kw of installed generating capacity. From its natural midvalley channel, the river has been diverted first into a prepared channel by the right bank, and will later be diverted through the tunnels. Rather more than 300,000,000 tons of fills are transported largely by belt conveyors. For this $1 billion project, resources have been mobilized on a global scale.

Erratum for “Design of Combined Service and Auxiliary Spillway at Auld Valley Reservoir”

Erratum for “Design of Combined Service and Auxiliary Spillway at Auld Valley Reservoir”

Design of Combined Service and Auxiliary Spillway at Auld Valley Reservoir

The design features are described of a single-entrance, dual-service spillway/auxiliary spillway at Auld Valley Reservoir of the Metropolitan Water District of Southern California. The spillway employs a modified side channel, in which the side wall opposite the primary weir may be overtopped during large spills from the reservoir. Another spillway entrance is thus created, leading into a secondary valley which becomes an auxiliary spillway. The indeterminate hydraulics of the intricate three-weir system are reviewed and a computerized solution is presented of the applicable theoretical relationships. Model studies are described, which were conducted to confirm the technical feasibility of the design concept and the flow distribution in the spillway system. A FORTRN IV computer program is presented in the appendix, together with a sample output of the program.

Hydrologic Design of Ramganga Dam Project

Hydrologic design of Ramganga Dam, a major dam in northern India, brings forth the special problems in countries where limited hydrologic data are available. The extension of the stage-discharge curve for the river necessitated backwater computations and development of suitable correlations because of the varying friction slope. Monthly rainfall-runoff relations from limited data have been used for transforming the rainfall data and for preparing a 60-year water budget to determine the useful reservoir yield and its probable variation. Optimum baseflow for use with unit hydrograph and design storms was estimated from the association between the flood-producing storm and the antecedent baseflow. Regional flood potential study was found to be a useful tool for checking design floods derived from design storms and unit hydrograph. Provision of an auxiliary spillway at a safe distance from the main dam reduces reservoir surcharge for extremely rare floods.

Box Canyon Hydroelectric Project

The unique design and construction of the Main Spillway Dam of the Box Canyon Hydroelectric Project is described in this paper, together with other project features, which include the powerhouse, diversion tunnel, forebay channel, and auxiliary spillway. The location and development of the site involved factors such as foundation, seasonal limitations on headwater elevation, and construction of the main spillway in a single low-flow season. The project is a run-of-the-river development, requiring the design of a dam and spillway which would not cause any increase in the natural flood water levels upstream from the project.