Diversion Weir Research Articles

Optimised multi-objective design of weir structures

Diversion head works, also called weirs or barrages, are structures constructed across rivers or canals to store water or raise the water level. The design of diversion weir structures involves calculating the depth, length and thickness of the horizontal and sloping aprons and sheet pile cut-offs. The design parameters of a diversion weir structure, which have complex non-linear relationships, are traditionally determined using empirically derived recommendations and iterations to achieve structural stability against failures due to scour, uplift, sliding, piping and overturning. However, current design approaches do not explicitly explore the trade-offs between the many relevant design objectives and thus fail to reveal possibly superior designs. A multi-objective optimisation design approach for a diversion weir structure is proposed in this article. A free and open-source code that can be used as a design tool is also provided. The method is demonstrated on a stylised design problem. The results show that the method reveals solutions with diverse balances of stability metrics and cost, with the optimal relationships of parameter values of components also varying based on the relative cost of the construction materials for sheet piles and aprons.

From a continuous thermal profile to a stepped one: The effect of run of river hydropower plants on the river thermal regime

AbstractBoth reservoirs and run of river power plants affect the thermal regime of rivers but despite the higher number of the latter few studies have focused on their effect. In this study, we investigated the water thermal regime of Serio River (Northern Italy), a subalpine river regulated by a reservoir and characterized by a cascade system of run of river power plants. Water temperature has been monitored continuously for more than 4 years at the extremes of 4 stretches subjected to water diversion and thermal alterations have been quantified. Our results show that hydroelectric power plants act locally causing a considerable thermal alteration that increases with the distance from the diversion weir. Indeed, within the by‐passed stretch, the rate of warming doubles the natural gradient (0.47°C/km vs. 0.19°C/km annually) with peaks in summer (0.73–0.90°C/km on average). By contrast, the run of river power plants keep the water temperature almost constant in the diversion channels. Thus, a cascade system of run of river plants shifts the overall riverine thermal regime from a continuous to a “stepped” longitudinal profile. Results highlight that the thermal effects of run of rivers plants are not negligible and should be considered and monitored continuously. Since there are thousands of hydropower plants powered by flowing waters it is time to consider their thermal impacts in environmental flow policies and bioassessment programs.

Three-dimensional numerical modelling of floods in river corridor with complex vegetation quantified using airborne LiDAR imagery

Excessive flood flow over the historic diversion weir in the vegetated Asahi River in Okayama Prefecture, Japan, was recently recorded for the first time after its renovation work. Fluvial researchers analysed the diversion discharge for flood mitigation measures through laboratory studies and conventional two-dimensional (2-D) depth-averaged simulations. The existing model was insufficient for simulation of certain phenomena such as flow resistance caused by vegetation branches and leaves and vertical flow distribution around the river corridor. Therefore, we developed a three-dimensional (3-D) vegetation resistance porous model by estimating topography, land cover, and vegetation distribution from airborne light detection and ranging (LiDAR) topo-bathymetry (ALB) data. Results show that the water level and flow regime were more reproducible than by referenced 2-D calculations when compared to space-time image velocimetry (STIV) data and field measurements. The diversion discharge designed using the proposed model is feasible with the current riverbed and vegetation conditions.

Spatial Variability of Silver Carp Population Demographics in a Large Tributary River

AbstractSilver Carp Hypophthalmichthys molitrix have expanded their range to encompass most of the Mississippi River basin, including much of the Missouri River. However, there is a paucity of information concerning Silver Carp in the Missouri River basin, especially in tributaries. Little is known about how Silver Carp function in these tributaries or how connectivity with a main‐stem river can influence population demographics within either system. The Kansas River is a tributary to the Missouri River and has multiple physical anthropogenic barriers creating varying levels of connectivity within the system, as well as with the Missouri River. These varying levels of connectivity, or lack thereof, provide a unique opportunity to examine population demographics in river segments separated by barriers. We collected Silver Carp from upstream and downstream of the first two barriers on the Kansas River in the summers of 2018 and 2019. No Silver Carp were captured upstream of a hydropower dam at river kilometer 84 but were found upstream of a water diversion weir at river kilometer 24. Catch rates of adult Silver Carp were lower in the reach above the weir, but Silver Carp caught in this reach exhibited greater growth rates than Silver Carp captured below the weir. Catch rates of juveniles were also lower in the reach above the weir. Limited connectivity within the Kansas River via the water diversion weir could influence size structure and catch rates of Silver Carp captured above and below the weir. Lack of juveniles above the weir indicates that reproduction may be limited in this reach, and river conditions below the weir may be more suitable for rearing juvenile Silver Carp. This information is important for understanding Silver Carp population demographics across a range of river environments, providing critical information for the development and implementation of broadscale control plans.

Evaluation of Drainage Water Detention Efficiency of Off-Line Ditch-Pond Systems and Its Influencing Factors

Ditch-pond systems can effectively alleviate the adverse effects of agricultural drainage on downstream canals and flood control in downstream areas. In this study, peak flow reduction rate (PFR) and drainage volume detention rate (DVD) are used to evaluate the effectiveness of an off-line ditch-pond system for reducing peak flow, retarding agricultural drainage water, and examining the key influencing factors. The results show that the PFR and DVD of the off-line ditch-pond system are significantly affected by three parameters: weir depth (Ld), weir width (Lw), and pond area-to-drainage area ratio (Ksp). Both the PFR and DVD increase with the increase in Ld, Lw, and Ksp. The effects of Ld and Lw on the PFR and the DVD are significant, whereas that Ksp is relatively small. Adjusting Ld and Lw increases both the PFR and DVD up to 80%. Specifically, Ld contributes 75% of the variations in the PFR and the DVD, and Lw affects only 17% of the PFR variations and 11% of the DVD variations. These findings confirm that an off-line ditch-pond system can be effectively used for the detention of agricultural drainage water. Thus, when such a system is designed with an appropriate diversion weir, the impact of agricultural drainage water on downstream canals and downstream areas can be reduced remarkably.

Irrigation Efficiency Performance Assessment of Modern Spate Irrigation Scheme: In Case of Kobo Woreda, North Wollo, Ethiopia

Spate irrigation is form of water management that is unique to arid and semi- arid area where floods are diverted in to cultivated crops by constructing diversion weir across the river. The general objective of the study was Assessments of irrigation efficiency Gobu-I and Gobu-II modern spate irrigation schemes. To achieve the study primary data were collected which includes measurement of soil moisture contents before and after irrigation, measurement of field discharge. The parameters used to compare the efficiencies at the farm field levels were application, storage and distribution uniformity efficiency. The application efficiencies of Gobu-I was 62.75, 72.61 and 77.56% and for Gobu-II was 57.88, 66.12 and 70.14%. The storage efficiencies of Gobu-I schemes were 89.06, 88.71 and 87.8% and for Gobu-II schemes were 90.97, 89.81 and 88.1%. Distribution efficiency for Gobu-I scheme were 92.65, 87.67 and 96.38% and For Gobu-II schemes were 85.05, 89.95 and 95.03% in the head, middle and tail field respectively. Application efficiencies of both schemes were not good because of it’s under limit but storage and distribution efficiencies were good. By strengthening the capacity of DA’s and farmer’s frequent evaluation and follow-up are critical to maintain sustainable performance of the modern spate irrigation schemes.

Assessment of Power Compeers Prospective of Gobecho Micro Hydropower Plant on Ganga River, Genale Dawa River Basin, Ethiopia

Micro hydropower helps the rural areas to supply power with off grid electrification. This study deals with the design of micro hydropower scheme in Gobecho kebele, Genale Dawa river basin, Ethiopia. The site for the construction of diversion weir is located upstream of the Ganga river in the kebele. The design were implemented based on the available hydrological data collected from 1991 to 2020 river discharge at different stations by selecting the one, which is near to the Gobecho catchment. Ererti is a station geographically near to Gobecho catchment by using GIS 10.7 application. The Gobecho peak probable discharge of 3.503m³/s is computed using log normal distribution after L-moment analysis. Based on this peak discharge, vertical drop weir and components of headwork structure designed and provided relevant dimensions. The proposed vertical drop weir has a height of 0.703m, crest length 10m and the design flow for a hydropower scheme is 0.132m³/s estimated by FDC. The water passes through trapezoidal power canal of a 0.35m width and a 0.43 height to a forebay tank. A forebay of size 9 × 1.3 × 1.7 is provided at the end of the power canal. Moreover, the water leads from forebay to a 0.24m diameter of penstock running one unit turbine and capacity of 25kw. The selected type of turbine for proposed plant is cross flow turbine. Finally, the quantity of calculated estimate cost is 50,000 USD and the B/C ratio of 1.48 provided for this micro hydropower project.

Analysis of ambo water supply source diversion weir sedimentation and assessing impact of land management practice through hydrological studies

Huluka River diversion weir, which diverts water supply for Ambo town, has been under severe sedimentation. In this study, the ArcSWAT model was applied to determine the sediment yield and sediment load of the Ungauged Huluka River watershed through the parameters transfer method. This particular study calibrated and validated the ArcSWAT model on the Guder River gauging station of watershed area 659 km2. The calibrated and validated best values were extended to all the sub-basin to estimate the sediment yield and sediment load of the ungauged Huluka River watershed. The ArcSWAT model was found certain with statistical performance procedures like regression coefficient, Nash–Sutcliffe and percentage of bias. The model was calibrated and validated with accepted statistical performance values on the monthly time scale. The statistical performance like regression coefficient, Nash and percentage of biased were dramatically increased upon the validation period to very good range according to Arnold et al. The estimated average sediment yield of the whole Guder sub-basin was found to be 4.3 (ton/ha). The annual average sediment load contributed from the Huluka River watershed was found to be 37.5 Kiloton/year. The estimated average annual sediment quantities at Guder gauging station and the whole Guder sub-basin were 344.8 Kiloton/year and 1.1 Megaton/year, with data ranging from 1998 to 2014 (17 years). Three different best management practices (BMPs) such as contouring, strip cropping and terracing were evaluated to see their effectiveness on the whole sub-basin. The sediment yield reduction with these BMPs was ranged from 58 to 62% at Guder hydro-gauging station with simulation period of 1998–2014. The sediment yield was strongly decreased to 76% with these BMPs at the Upper Huluka watershed.

Evaluating the impact of hydropower on downstream migrating anguillid eels: Catchment-wide and fine-scale approaches to identify cost-effective solutions

Hydropower is an increasingly popular source of renewable and ‘green’ (in terms of emissions) energy, but reduced longitudinal connectivity and diverting flow through turbines can have negative impacts on catadromous anguillid eel species that have declined globally. There is an urgent need for environmental managers to perform remediation actions, such as protecting flows for migratory fish and providing passage solutions at infrastructure, under increasing legislative pressure. To deliver this, a more comprehensive understanding of eel migration in catchments with hydropower is required. Here, we illustrate the importance of catchment-wide and fine-scale acoustic telemetry, coupled with the influence of eel maturation (i.e. sex steroid levels), to determine the impact of Wairua run-of-river Power Station (WPS) on downstream migrating shortfin eels (Anguilla australis; n = 25) in Wairua River, New Zealand. Migration speed through the unregulated reach upstream of WPS was positively correlated with flow, but not eel length or sex steroids. Three eels passed a diversion weir (DW) to follow the natural watercourse and eight entered the WPS canal. Eels predominantly entered (95.2%) and were last detected (85.7%) in WPS forebay during hours of darkness. Eleven (52%) of the 21 eels that entered WPS forebay were impinged or entrained, all when three or four turbines were in operation (power generation >3.04 MW). Ten (48%) passed WPS spillway during significantly higher spill than impinged or entrained eels, with four passing during no turbine operation, after experiencing high flows near the intake (multiple receivers in WPS forebay used to quantify fine-scale behaviour). On average, eels were impinged or entrained at WPS significantly quicker (6.40 ± 11.13 days) than eels that entered the spillway (25.17 ± 15.12 days), but eel length and sex steroids did not significantly influence fate. Of the eels that migrated through the entire 55 km study reach, passage time at DW and WPS equated to 0.01–0.02% and 47.62–92.17% of their migration, respectively. Mitigation for WPS (and similar power schemes) should focus on operational or physical changes at DW to minimise eels entering power station forebay(s). Turbine shutdowns, ensuring WPS spillway is available and the provision of a bypass channel in WPS forebay are also discussed as ways to conserve the species with the potential to save costs for water resource managers.

Toward better institutional setup in spate irrigation system: the case study of Yandafero-Konso lowland spate irrigation system, Ethiopia

The Yandafero spate irrigation system, both traditional and modern, has experienced community floodwater management for the last 25 years. However, most of the intakes were severely damaged by high flood. The weak relationship between governmental organization and water users, absence of policy and institutional structure for operation and maintenance, result conflicts on water sharing at upstream and downstream, then lead to collapse or dysfunctional of scheme. Hence, the study was conducted to evaluate the existing performance of institutional setup concerning operation and maintenance, water sharing and conflict management, provision of self-finance and performance impacts on agricultural productivity and recommendation that build strengths and address limitations of current institutions for better spate flow management in Yandafero-Konso lowland. Primary data including socio-economic data like household income were collected through a household survey and questionnaires. Interview, focus group discussion and field visit were employed to understand operational and maintenance activities. Grey literature and documents were also used to realize the general description and role of organizations in Yandafero spate system. Then five principals: right to organize, operation and maintenance of infrastructure, water sharing dynamics, conflict resolution mechanism and facilities for self-finance were developed to evaluate the existing institutional arrangement. As the study showed that farmers were organized under formal and informal Irrigation Water User Cooperative (IWUC), out of the nine proposed IWUCs, only three of them got the right to be organized with clearly stated (written) responsibilities. Oneya and Potota sub-schemes were with poor status of diversion weir such as damaging of headwork, barred gate, malfunction of flood flash that results in high accumulation of sediment on the weir. Though water rights and distribution rule were similarly established among three schemes, their performance was varying. In Potota sub-scheme, negligence of enforcement of water distribution regulation and codification was experienced compared to Oneya (56.7%) and Tarakoma (43.3%). There was good performance of IWUC at Oneya and Tarakoma sub-schemes regarding the construction irrigation canals and ensuring equal floodwater distribution. Conflict resolution mechanism was established only at Oneya and Tarakoma sub-schemes. Farmers practiced credit and loan facilities for self-finance through formal cooperative mechanisms. In Potota sub-scheme, the average annual production before and after the improvement of diversion weir was the same ( 4000 kg per annual).

Desilting Basin Efficiency Estimation for Run-of-River Small Hydropower Plants

Suspended sediment concentration and discharge are important factors affecting the operational reliability of run-of-river small hydro power (SHP) plants. Elimination of sediment transported with the flow across the turbines of run-of-river plants is therefore a critical issue for the sustainability of the SHP industry. Comprise of a small diversion weir throughout a stream, the SHP plants does not have space to pile sediments but should be able to divert the incoming bed loads to the river downstream. Sediments in the water entering through the turbines with extreme velocity erode the contact surfaces of turbine mechanisms which results in reduced hydraulic efficiency and increased maintenance cost. Subsequently, desilting basins have become an essential part of the water conductor system of run-of-river SHP to reduce the impact of damage due to suspended sediment. Desilting basins are devised as settling basins to settle sediments larger than a targeted size. They are constructed just after power intake and discharge is despatched through them before pass into the head race tunnel. This study is aimed to estimate the sediment removal efficiency of SHP desilting basins based on data recorded at the intake of a run-of-river SHP. Considering the hydrological variability, probabilistic approach was used to obtain mathematical function for the probability density of suspended sediment concentration (SSC) based on the recorded data.

Nepal Earthquake 25 April 2015: Hydro projects damaged, risks and lessons learned for design considerations

The 25 April 2015 Nepal earthquake of magnitude 7.8 epicentre at Gorkha and magnitude 7.3 aftershocks on 12 May epicentre at Dolakha had devastating impacts on 14 districts including Kathmandu, capital city of Nepal. Death toll was nearly 9,000 and hundreds of thousands of inhabitants became homeless. The earthquake severely damaged mainly surface structures of hydro projects, access roads, clay mortar stone masonry houses and structurally weak concrete houses. Landslides, rock falls, debris flow, liquefaction, river damming, Landslides Dammed Outburst Flood (LDOF) and Glacial Lake Outburst Flood (GLOF) are expected earthquake-induced hazards. However, landslides and grounds shaking were responsible for major damaged. A total of 15 hydro projects in operations and under construction were affected by the earthquake. In hydro projects damages were recorded in surface structures such as power house, settling basin, penstock pipes, and diversion weir constructed at base of steep terrains. For instance, surface penstock pipe, lying at base of rock cliff, of running 40 MW Upper Bhote Koshi Project was ruptured by rock falls and as a result flooded surface powerhouse located downstream by water from penstock and headrace tunnel. Similarly, diversion weir, surface settling basin and headrace penstock pipe of running 5 MW Mialung Project were also severely damaged by slides and rock falls. On the other hand, only minor cracking of sprayed concrete at corners and protruded edges in underground structures were observed. In hydro projects, there is a practice of considering seismic load in design of structures but the effects of earthquake induced hazards were not foreseen. This devastating earthquake gave good lessons for design considerations of hydro projects in future. This article summarises earthquake damage, risks and lessons learned for Hydro projects in Nepal.

Evaluation of Rubber Dams for SHP in India

India is blessed with great Himalayas as well as hilly areas in peninsular and central areas providing opportunity for hydro power at all scale including Small Hydropower (SHP) development. Water is diverted from the streams for hydro power generation using suitable diversion structures. Conventional types of raised-crest weirs are not well suited for hill streams having steep slopes and boulder movement during floods. Inflatable dam or also known as rubber dam is one type of diversion structure to control and regulate the water for power generation.The experience of inflatable dams in India is very limited even though worldwide over 4,000 installations exist and more than 10 manufacturers offer this type of weir. There are only three installations so far used for irrigation or municipal purposes and not a single rubber dam for hydropower projects in India. For selecting a suitable diversion structure, economic and technical aspects are to be carefully considered. Different types of diversion weirs including rubber dam used for diverting water for Small Hydropower (SHP) projects are studied and presented. The design of diversion weir depends on the quantity of water withdrawal and width of stream. This study is an attempt to study the rubber dam technology for Small Hydropower in India. Five different sites were selected for the present study. Rubber dam was also compared with conventional raised gravity weir, trench weir (Tyrolean), bush and boulder weir and “mathu bund” (a local name). The life cycle of these different types of weirs for same hydraulic conditions and for different discharge were computed and compared with that of imported rubber dam as well as Indian rubber dam. The cost of rubber dam was estimated based on personal communications with the experts of manufacturers and practitioners of the subject area, as well as case studies of already constructed rubber dams in India installed for purposes other than hydropower. Operation and maintenance cost and different losses on account of head, water loss and repair were taken into account for different types of weirs for calculating life cycle cost. Possible damage that may be caused by major flood for different types of weir was also calculated monetarily in terms of power loss. The ease of inflation and deflation reduces the flood damage cost, O & M cost, sediment removal cost and repair work cost. With the comparative analysis, it is found that average life cycle cost of raised gravity weir, bush and boulder, mathu bund and trench weir (Tyrolean), is 2,3, 5 and 6 times respectively more than imported rubber dam. Life cycle cost of Indian rubber dam and average life cycle cost of imported rubber dam is about three times more than Indian rubber dam. It is recommended to use inflated weir in Small Hydropower projects being cost effective and energy efficient.

Assessment of flow regime alterations over a spectrum of temporal scales using wavelet‐based approaches

AbstractThe full range of natural flow regime is essential for sustaining the riverine ecosystems and biodiversity, yet there are still limited tools available for assessment of flow regime alterations over a spectrum of temporal scales. Wavelet analysis has proven useful for detecting hydrologic alterations at multiple scales via the wavelet power spectrum (WPS) series. The existing approach based on the global WPS (GWPS) ratio tends to be dominated by the rare high‐power flows so that alterations of the more frequent low‐power flows are often underrepresented. We devise a new approach based on individual deviations between WPS (DWPS) that are root‐mean‐squared to yield the global DWPS (GDWPS). We test these two approaches on the three reaches of the Feitsui Reservoir system (Taiwan) that are subjected to different classes of anthropogenic interventions. The GDWPS reveal unique features that are not detected with the GWPS ratios. We also segregate the effects of individual subflow components on the overall flow regime alterations using the subflow GDWPS. The results show that the daily hydropeaking waves below the reservoir not only intensified the flow oscillations at daily scale but most significantly eliminated subweekly flow variability. Alterations of flow regime were most severe below the diversion weir, where the residual hydropeaking resulted in a maximum impact at daily scale while the postdiversion null flows led to large hydrologic alterations over submonthly scales. The smallest impacts below the confluence reveal that the hydrologic alterations at scales longer than 2 days were substantially mitigated with the joining of the unregulated tributary flows, whereas the daily‐scale hydrologic alteration was retained because of the hydropeaking inherited from the reservoir releases. The proposed DWPS approach unravels for the first time the details of flow regime alterations at these intermediate scales that are overridden by the low‐frequency high‐power flows when the long‐term averaged GWPS are used.

Installation of Impact Plates to Continuously Measure Bed Load: Elwha River, Washington, USA

AbstractIn 2008 and 2009, a series of bed load impact plates was installed across a channel spanning weir on the Elwha River, Washington. This is the first permanent installation of its kind in North America and one of the largest anywhere. The purpose of this system is to measure coarse bed load during and after the removal of Elwha and Glines Canyon Dams. It is estimated that 21 million m3 of sediment have accumulated behind both dams, with 45–50% of the total accumulated volume expected to be eroded through natural processes. The impact plate system consists of 72 plates installed at a diversion weir downstream from both dams and 5 km upstream from the river mouth. Of the 72 plates, 46 are instrumented with a geophone and 26 with an accelerometer. Collection of physical bed-load data for calibration of the geophone plates has begun, with additional measurements to be collected in the future. This paper describes the specifics of the Elwha impact plate system and the ongoing process to collect bed-load...

Assessment of Irrigation Water Quality and Suitability for Irrigation in the Fincha’a Valley Sugar Estate, Nile Basin of Western Ethiopia

A number of factors like geology, soil, effluents, sewage disposal and other environmental conditions in which the water stays or moves and interacts are among the factors that affect the quality of irrigation water. This study was conducted to determine the quality and suitability of different water sources for irrigation purpose in Fincha’a Valley Sugar Estate (FVSE), within the Nile Basin of Western Ethiopia. A total of 80 water samples were collected from different sources viz., reservoir, rivers, diversion weir, canals, pump stations, drains, and groundwater of the study area. Physico-chemical properties including electrical conductivity (EC), hydrogen ion concentration (pH), total dissolved solids (TDS), major cations (Ca, Mg, K, Na) and anions (HCO3 and Cl) were analyzed in the laboratory and sodium adsorption ratio (SAR), residual sodium carbonate (RSC) and permeability Index (PI) were calculated from the major cations and anions studied for the criteria of irrigation water quality and suitability for irrigation. The study revealed that the values of EC, pH and TDS, and the amount of Cl-, HCO3, Na+, K+ , Ca2+ and Mg2+ varied from 100 to 730 µS cm-1, 6.6 to 7.3, 64 to 467.20 mg l-1,and 2.8 to 6.8, 2.04 to 5.6,3.8 to 7.8, 0.05 to 0.26, 8.4 to 19.9, 1.4 to 3.7 mmol l-1 and SAR, RSC, the PI values varied from 0.4 to 3. 9, -13 to -6.4 and 26.34 to 49. 9 %, respectively. The cationic and anionic constituents and SAR values of the samples increased from the upstream to the downstream. This is clear indication of the impacts of agricultural activities of the upstream and long-term irrigation in the downstream on the quality and suitability of water for irrigation purpose. If this trend continues, the gate for secondary salinization becomes significant. This necessitates the undertaking of certain management measures in the area for sustainability and productivity of the irrigation system in the FVSE.

Computer Assisted Preliminary Design of Run-Of-River Plants

Run-of-river type hydroelectric power plants generate electrical energy by using a certain portion of the available flow in the river. A computer program called MINI-HPD is developed to perform the hydraulic design of run-of-river plants. This program, which runs under the Windows operating system, is developed in C# programming language. MINIHPD is capable of performing hydraulic design of structural components of diversion weir with lateral intake and overflow spillway, canal, forebay, and penstock. In addition, it can determine the optimum design discharge, optimum installed capacity, and optimum penstock diameter for this type of plants. It is desired to have quick successive runs under various scenarios and combinations of relevant parameters. An application is presented to illustrate the use of the program

The impact of hydrotechnical facilities on island avifauna: a case study of the middle Vistula River

The study was conducted in the years 1994-2006 in the middle of the Vistula River between Wróble and Kochów (416th – 418th km of the waterway). The presence of islands and steep banks makes it a key place for nesting avifauna, including a number of endangered species. The aim of this paper is to present the impact of hydro-technical facilities (a diversion weir) on habitat changes, and consequently on the abundance and distribution of birds that inhabit this part of the river. A cross-divider in the riverbed (weir) connecting the bank of the river with one of the islands increased the flow rate and pushed the current to the middle of the river, directing it towards the islands. The result of these changes was a sudden erosion of the sandy, the high slope at the top of the island II, a partition of this island into two parts, and a slow erosion of the island located near the left bank (island IV, Fig. 1B). Lack of fixed, steady flow along the right bank resulted also in a considerably faster succession of vegetation on the island I and slow shallowing of the channel between the island and the bank. As a result, the area of sandy habitats, most valuable to nesting birds, decreased disproportionately faster than the area of the whole islands (Table 1). In the years 2001-2002, when the island I was completely united with the right bank and the islands 0 and I were connected to each other, a width of the riverbed at this point decreased from 870 m to 710 m, i.e. by more than 20 % (Fig. 1).

Proposal of new return flow analysis by replacement-in-order method for paddy irrigation water

Return flow and repeated use of irrigation water for paddies is the most important issue in the Asian monsoon region, because sometimes this water is applied in greater quantity than that of evapotranspiration plus percolation. A new return flow analysis, the “replacement-in-order method”, which introduces a unique numbering system for very complicated irrigation and drainage networks, is proposed for the main canal with the dual purposes of irrigation and drainage. The method is applied to the Shichika irrigation district in the ordinal (season) irrigation period, resulting in a return flow ratio of 45 % for the entire area. Of this amount, 25 % is available for irrigation again. The remaining 20 % is unavailable, because the return flow discharged directly into a canal lacking a diversion weir in the drainage system, or into the Japan Sea. The return flow ratio is very different at the main canal location, from no return flow to 88 %. With the aid of the above method, theoretical analysis of return flow for paddy irrigation water can be done. This includes the deterministic return flow ratio inside and outside the irrigation area, plus precise information of return flow ratios at various main canal locations and routes of irrigation and drainage water.

Age and hydrological significance of lichen limits on sandstone river channels near sydney, australia

Trimmed lichen communities (lichen limits) are abrupt changes from a lichen community to a scoured bare rock surface and have been used to determine bankfull channel capacity on bedrock channels and their response to the combined disturbances of flow regulation and climate change. They can also be used to set flushing flows in bedrock channels. In sandstone gorges of the Nepean River, Australia, the crustose lichen, Lecidea terrenaNyl, was common at both gorge and cemetery (sandstone headstones) sites, enabling construction of growth curves for above and below dam areas. Growth curves were used to date lichen colonisation of sandstone surfaces in rivers. The oldest, highest lichen limit at all sites represented the pre‐flow regulation lichen community because its characteristics above and below epean am were similar and were trimmed to a level that produced consistent discharges across a range of catchment areas. They corresponded to return periods of less than 2 years on the annual maximum series and was developed during the flood‐dominated regime of 1857–1900. Lichen limits form by the phycobiont dominating the mycobiont and hence degrading lichen thalli due to water inundation causing weak or dead thalli to be scrubbed from the rock surface. Trimming to the unregulated lichen limit represents a small flood of frequent occurrence appropriate for flushing bedrock channels. A lower lichen limit was only found below a diversion weir and was formed by frequent dam spills between 1950 and 1952 during an extraordinary wet period at the start of the between 1949 and 1990. Lichens colonised exposed sandstone between the level of frequent flows from 1949 to 1952, and the high lichen limit. On the von iver, an additional lower limit reflected a massive downward shift in flow duration following the start of interbasin diversions to ollongong in 1962.