Multivariate Dam-Site Flood Frequency Analysis of the Three Gorges Reservoir Considering Future Reservoir Regulation and Precipitation

Under a changing environment, the current hydrological design values derived from historical flood data for the Three Gorges Reservoir (TGR) might be no longer applicable due to the newly-built reservoirs upstream from the TGR and the changes in climatic conditions. In this study, we perform a multivariate dam-site flood frequency analysis for the TGR considering future reservoir regulation and summer precipitation. The Xinanjiang model and Muskingum routing method are used to reconstruct the dam-site flood variables during the operation period of the TGR. Then the distributions of the dam-site flood peak and flood volumes with durations of 3, 7, 15, and 30 days are built by Pearson type III (PIII) distribution with time-varying parameters, which are expressed as functions of both reservoir index and summer precipitation anomaly (SPA). The multivariate joint distribution of the dam-site flood variables is constructed by a 5-D C-vine copula. Finally, by using the criteria of annual average reliability (AAR) associated with the exceedance probabilities of OR, AND and Kendall, we derive the multivariate dam-site design floods for the TGR from the predicted flood distributions during the future operation period of the reservoir. The results indicate that the mean values of all flood variables are positively linked to SPA and negatively linked to RI. In the future, the flood mean values are predicted to present a dramatic decrease due to the regulation of the reservoirs upstream from the TGR. As the result, the design dam-site floods in the future will be smaller than those derived from historical flood distributions. This finding indicates that the TGR would have smaller flood risk in the future.

Influence of a Post-dam Sediment Pulse and Post-fire Debris Flows on Steelhead Spawning Gravel in the Carmel River, California

Spawning gravel scarcity is a limiting factor for successful recovery of federally-threatened anadromous fish like steelhead of central California. A BACI-experimental design using bed particle counts from 2013 through 2021 shows that spawning-sized gravel (32–90 mm) diminished downstream of the former San Clemente Dam site in 2017, following dam removal in 2015. High flows in 2017 transported a pulse of sand and fine-gravel that filled pools and runs throughout the river below the dam. The bed material in the 3 km closest to the dam remained too coarse for redds in riffles and too fine in pools and runs. Time-series bathymetric data of the Los Padres Dam reservoir located in the upper Carmel watershed shows that nearly all bed material (including spawning gravel) in the upper Carmel River watershed was recruited during wet winters that immediately followed expansive wildfires. We studied that effect in detail following the Carmel Fire of August 2020, which preconditioned the slopes adjacent to the Carmel River for debris flows. Our analysis of several fire-mediated debris flows in 2021 show that they contained virtually no mud and held approximately 45% spawning-sized gravel. Although the debris flows contained abundant spawning gravel, and several flow snouts terminated in the Carmel River, the material was dispersed downstream rather than forming bars and patches that could be used for steelhead nest building. The generally small volume of material in the flows relative to the size of the river channel and impediments to debris flow runout limited the contribution of spawning-size gravel to the river.

Exploring the Impact of Resettlement on Women: A Case Study of the Nam Mang 3 Hydropower Dam in Central Laos

<p>Over the last decade, construction of hydropower dams has increased rapidly around the world, including in developing countries. For many countries including Laos, energy production and export play a significant role in promoting and boosting economic growth and development. Energy production generates substantial revenue and foreign exchange from exporting electricity and expands economic activity domestically. However, construction of hydropower dams also causes negative effects on the people who live at and around the dam site. Some local communities have been affected indirectly, while others require relocation to other areas bringing significant change, including for women. This research explores the impact of resettlement from hydropower dam creation on women by using the Nam Mang 3 hydropower dam in central Laos as a case study. This dam, completed in 2005, required the relocation of approximately 150 households from two villages at the dam site. The research draws on a social constructivist epistemology, qualitative methods including semi-structured interviews, and analysis of relevant policy documents. Interviews involved 18 participants including both male and female from the three affected villages. Results indicate that the resettlement of villagers by the Nam Mang 3 hydropower dam has generally improved living conditions of the resettled communities. Women were found to have greater opportunities to benefit from home-based business, employment and wage labouring. In addition, with better access to modern facilities and services, women have been able to save greater time from agricultural activities and divert this time saving to other economic activities. Overall, access to water supplies, roads, and transport have reduced women’s workload significantly. Access to improved health services and facilities have also improved women’s wellbeing. Girls have greater opportunities to attend school and seek employment in towns. However, this research identified some challenges experienced by the resettled such as the reduction of agricultural and grazing land area, and that new livelihood options were not accessible to all women. Instead of these challenges, the experience with the Nam Mang 3 hydropower project has highlighted one of the key lessons learnt that is worth highlighting for future resettlement programs, which is to have the resettlers fully engaged in the entire process of resettlement and livelihood strategy development.</p>

Exploring the Impact of Resettlement on Women: A Case Study of the Nam Mang 3 Hydropower Dam in Central Laos

<p>Over the last decade, construction of hydropower dams has increased rapidly around the world, including in developing countries. For many countries including Laos, energy production and export play a significant role in promoting and boosting economic growth and development. Energy production generates substantial revenue and foreign exchange from exporting electricity and expands economic activity domestically. However, construction of hydropower dams also causes negative effects on the people who live at and around the dam site. Some local communities have been affected indirectly, while others require relocation to other areas bringing significant change, including for women. This research explores the impact of resettlement from hydropower dam creation on women by using the Nam Mang 3 hydropower dam in central Laos as a case study. This dam, completed in 2005, required the relocation of approximately 150 households from two villages at the dam site. The research draws on a social constructivist epistemology, qualitative methods including semi-structured interviews, and analysis of relevant policy documents. Interviews involved 18 participants including both male and female from the three affected villages. Results indicate that the resettlement of villagers by the Nam Mang 3 hydropower dam has generally improved living conditions of the resettled communities. Women were found to have greater opportunities to benefit from home-based business, employment and wage labouring. In addition, with better access to modern facilities and services, women have been able to save greater time from agricultural activities and divert this time saving to other economic activities. Overall, access to water supplies, roads, and transport have reduced women’s workload significantly. Access to improved health services and facilities have also improved women’s wellbeing. Girls have greater opportunities to attend school and seek employment in towns. However, this research identified some challenges experienced by the resettled such as the reduction of agricultural and grazing land area, and that new livelihood options were not accessible to all women. Instead of these challenges, the experience with the Nam Mang 3 hydropower project has highlighted one of the key lessons learnt that is worth highlighting for future resettlement programs, which is to have the resettlers fully engaged in the entire process of resettlement and livelihood strategy development.</p>

Sensitivity analysis for dam breach parameters using different approaches for earth-fill dam

The prediction of dams breach geometry crucial in studies of dam breaking. The hydrographs characteristics of flood that resulting from breaking of dam is mainly depend on the geometry of breach and the time formation of breach. Five approaches (Froehlich, Macdonald and Langridge-Monopolis, Von thun & Gillete, USBR and Singh % Snorrason) was used in order to predict dam breach parameters (breach width, breach side slope, breach formation time). The Sensitivity analysis was performed in order to assess the effect of each parameter on the resulting hydrograph of the flood. HEC-RAS model was used to calculate the effect of each parameter on the hydrograph of the flood that resulted. The width of breach (Bavg), side slope (z) and formation time of breach (tf) increased by 25%, 50%, 75% and 100% and decreased by 25%, 50% and 75%, respectively. Flood hydrograph was estimated at the dam site for each case. Sensitivity analysis was performed in order to check the effect of each parameter of breach and time of breaching. Sensitivity analysis was performed with Froehlich method with the mode of overtopping failure and maximum operating level at 107.5 meter above sea level. Result of sensitivity analysis show that peak discharge and time to reach it is adequately sensitive to breach side slope, highly sensitive to the breach formation time and less sensitive to breach width.

GEOTECHNICAL INVESTIGATION OF THE PROPOSED IFE DAM SITE AT KAJOLA VILLAGE, ILE-IFE, SOUTHWESTERN NIGERIA

Geological and geophysical investigations were conducted to assess the competence and structural integrity of the foundation site of the proposed Ife-dam at Kajola Village, Ile-Ife, Southwestern Nigeria. Geological investigation along the two (2) proposed dam axes revealed that the overburden material is loose to dense with angular shearing resistance (ɸ) of 27o to 41o. The soils are predominantly elastic silts; cohesive with considerable strength and stability. Geophysical investigation involving the Schlumberger Vertical Electrical Sounding delineated four (4) lithologies namely: topsoil with resistivity of 69 – 558 Ωm and thickness between 1.5 and 4.0 m; weathered sandy layer with resistivity from 123 – 586 Ωm and thickness between 6.5 and 20.4 m; partially weathered/ fractured basement with resistivity from 60 – 220 Ωm and thickness between 6.5 and 14.0 m; and the fresh basement rock with resistivity from 1337 – 10683 Ωm. There are indications of fractures at a depth of 32 m beneath Axis B extending to Axis A at a depth of 35 m. The subsurface materials are suitable to host a dam. Axis B is more appropriate for the dam axis, although the fracture zone should be factored into the design of the dam to prevent water seepage.