Progress in the Research on Benefit-sharing and Ecological Compensation Mechanisms for Transboundary Rivers

Transboundary rivers have important geopolitical and geo-economic connotations, but riparian states of transboundary rivers are often driven by their own rapid population growth and economic development to be-come involved in regional conflicts about the development and use of water resources. Therefore, finding a balance between the need for fair and reasonable development of water resources and the effective protection of environment from an ecological perspective has become a major problem faced by the international community. This paper begins with consideration of international water laws related to transboundary rivers and then reviews advances in the research on benefit-sharing, ecological compensation mechanisms, and adaptive management systems. We believe that existing international water laws form a complete legal system and that more attention needs to be paid to transboundary cooperation and sustainable water resource use. With respect to how transboundary water conflicts are resolved, there is a trend to move away from single water resource allocation (a zero-sum game) to benefit-sharing in order to achieve a win-win situation for riparian states, but there are still some difficulties in transboundary ecological compensation. In China, the central government has paid attention to horizontal ecological compensation between upstream and downstream, offering guidance to promote establishment of inter-province ecological compensation. Based on existing practice, horizontal ecological compensations are still in their infancy, small in scale, supported by a weak legal system, lacking market mechanisms to encourage their use and relying on fiscal transfers as the method of payment. In the future, China will need to intensify its research on legal system development, international cooperation, and benefit-sharing as these impact transboundary water resources. Because government can be seen as a management department with multiple identities (enabler, regulator and buyer), to improve adaptive transboundary ecological compensation mechanisms, government must develop as soon as possible data sharing platforms, standards of water consumption behaviors and intergovernmental policies (or ordinances).     

Vegetation turnover in a braided river: frequency and effectiveness of floods of different magnitude

This work addresses the temporal dynamics of riparian vegetation in large braided rivers, exploring the relationship between vegetation erosion and flood magnitude. In particular, it investigates the existence of a threshold discharge, or a range of discharges, above which erosion of vegetated patches within the channel occurs. The research was conducted on a 14 km long reach of the Tagliamento River, a braided river in north‐eastern Italy. Ten sets of aerial photographs were used to investigate vegetation dynamics in the period 1954–2011. By using different geographic information system (GIS) procedures, three aspects of geomorphic‐vegetation dynamics and interactions were addressed: (i) long‐term (1954–2011) channel evolution and vegetation dynamics; (ii) the relationship between vegetation erosion/establishment and flow regime; (iii) vegetation turnover, in the period 1986–2011. Results show that vegetation turnover is remarkably rapid in the study reach with 50% of in‐channel vegetation persisting for less than 5–6 years and only 10% of vegetation persisting for more than 18–19 years. The analysis shows that significant vegetation erosion is determined by relatively frequent floods, i.e. floods with a recurrence interval of c. 1–2.5 years, although some differences exist between sub‐reaches with different densities of vegetation cover. These findings suggest that the erosion of riparian vegetation in braided rivers may not be controlled solely by very large floods, as is the case for lower energy gravel‐bed rivers. Besides flow regime, other factors seem to play a significant role for in‐channel vegetation cover over long time spans. In particular, erosion of marginal vegetation, which supplies large wood elements to the channel, increased notably over the study period and was an important factor for in‐channel vegetation trends. Copyright © 2014 John Wiley & Sons, Ltd.     

Delivering environmental flows in the Murray-Darling Basin (Australia)—legal and governance aspects

Abstract

The hydrology of water-dependent ecosystems around the world has been altered as a result of flow regulation and extraction for a variety of purposes including agricultural and urban water supply. The flow regime of the Murray-Darling Basin in Australia is no exception, with attendant impacts on the health of the environment. Restoration of parts of the flow regime is a key feature of environmental flow delivery. However, environmental flow delivery in a system that is managed primarily to provide a secure and stable supply for irrigation presents challenges for managers seeking to return more natural flow variability in line with ecosystem requirements. The institutional arrangements governing releases of water from storage can influence the ability of managers to respond to natural cues, such as naturally rising flows in a river. As such, the legal and governance aspects of environmental flow delivery are likely to be important influences on the outcomes achieved.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Banks, S.A. and Docker, B.B., 2014. Delivering environmental flows in the Murray-Darling Basin (Australia)—legal and governance aspects. Hydrological Sciences Journal, 59 (3–4), 688–699.     

Assessment of environmental flows under limited data availability: case study of the Acheloos River,Greece

Abstract

The lower course of the Acheloos River is an important hydrosystem in Greece, heavily modified by a cascade of four hydropower dams upstream, which is now being extended by two more dams in the upper course. The design of the dams and hydropower facilities that are in operation has not considered any environmental criteria. However, in the last 50 years, numerous methodologies have been proposed to assess the negative impacts of such projects to both the abiotic and biotic environment, and to provide decision support towards establishing appropriate constraints on their operation, typically in terms of minimum flow requirements. In this study, seeking a more environmentally-friendly operation of the hydrosystem, we investigate the outflow policy from the most downstream dam, examining alternative environmental flow approaches. Accounting for data limitations, we recommend the basic flow method, which is parsimonious and suitable for Mediterranean rivers, whose flows exhibit strong variability across seasons. We also show that the wetted perimeter–discharge method, which is an elementary hydraulic approach, provides consistent results, even without using any flow data. Finally, we examine the adaptation of the proposed flow policy (including artificial flooding) to the real-time hydropower generation schedule, and the management of the resulting conflicts.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Efstratiadis, A., Tegos, A., Varveris, A., and Koutsoyiannis, D., 2014. Assessment of environmental flows under limited data availability: case study of the Acheloos River, Greece. Hydrological Sciences Journal, 59 (3–4), 731–750.     

2D NUMERICAL SIMULATION OF FLOOD AND FLUVIAL PROCESS IN THE MEANDERING AND ISLAND-BRAIDED MIDDLE YANGTZE RIVER

The characteristics of water flow and sediment transport in a typical meandering and island-braided reach of the middle Yangtze River is investigated using a two-dimensional （2D） mathematical model. The major problems studied in the paper include the carrying capacity for suspended load, the incipient velocity and transport formula of non-uniform sediment, the thickness of the mixed layer on the riverbed, and the partitioning of bed load and suspended load. The model parameters are calibrated using extensive field data. Water surface profiles, distribution of flow velocities, riverbed deformation are verified with site measurements. The model is applied to a meandering and island-braided section of the Wakouzi-Majiazui reach in the middle Yangtze River, which is about 200 km downstream from the Three Gorges Dam, to study the training scheme of the navigation channels. The model predicts the processes of sediment deposition and fiver bed erosion, changes of flow stage and navigation conditions for the first 20 years of impoundment of the Three Gorges Project.     

Invertebrate recolonisation of previously dry channels in the Rakaia River

Recolonisation of previously dry channels by stream invertebrates was studied in the Rakaia River during winter 1981 and summer 1982. The winter experiment continued for 42 days, with stable low flows, whereas the summer experiment was characterised by fluctuating large flows which caused it to be abandoned after 27 days. The fauna was dominated numerically by Chironomidae, a leptophlebiid mayfly (Deleatidium), and oligochaetes during the winter, and by Deleatidium alone during the summer. Recolonisation was considered complete after 33 days in winter and 15 days in summer. Flow fluctuations were the main factor affecting colonisation rates, and it was assumed that drift was the main source of colonising animals. Small freshes during low‐flow periods in winter resulted in a rapid increase in total density of invertebrates and number of taxa present and also affected the population structure of Deleatidium larvae in colonisation baskets. Before these freshes numbers had increased steadily over a 27 day period. In summer large floods during high flow periods initially decreased benthic invertebrate numbers in samples but numbers increased rapidly once the flood had passed. This appears to be the first study of its kind on a large unstable river system.     

Critical depths for passage in braided rivers,Canterbury, New Zealand

Riffles and points of divergence of branch channels in braided rivers are critical controls upon passage of fish and recreational boats because they are points at which depths are at a minimum. Depths on randomly selected riffles were measured in braided reaches of the Ashley, Hurunui, and Rakaia Rivers and related to discharge; minimum depths encountered in extended reaches of these rivers at a range of flows have also been measured. The data can be used to predict minimum available passage depths at a specified flow, or conversely, to predict the discharge required to maintain a specified minimum passage depth. However, presently available estimates of critical minimum depths required for various instream uses (migration of salmonids, jetboating) appear excessively conservative, and minimum depth requirements must be more accurately determined before instream flow needs can be properly assessed.     

The response of braided planform configuration to flow variations,bed reworking and vegetation: the case of the Tagliamento River,Italy

Morphological features of braided rivers (bars, channels and pools) experience major changes in area, shape and spatial distribution as a response to (i) the pulsation of discharge during a flood and (ii) the bed evolution induced by floods. In this work, at‐a‐station relationships between water level and planform configuration were investigated on the Tagliamento River, a large gravel‐bed braided river in northeast Italy, over a 2‐year study period comprising three bankfull events and several small‐to‐medium floods. The analysis was performed on two 1‐km‐long reaches, characterized by different riparian vegetation cover. Ground‐based images with an hourly temporal resolution were acquired using software‐controlled, digital cameras. Bars, channels, pools and vegetated patches were manually digitized on more than 100 rectified images. Sequences of constant‐level images spanning the study period were used to quantify the impact of floods on the stability of at‐a‐station relationships and on the turnover rate of water bodies. The analysis shows that wetted area increased almost linearly with water level in both reaches. The average number of branches per cross‐section peaked at intermediate flow levels, increasing from 2 at low flow up to 6–7. The number of branches displayed the largest fluctuations over time, with significant changes produced also by moderate floods. Turnover rates were high in both reaches, with more than 30% of wetted areas at low flow converting into bare gravel in less than 2 months. Vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer, deeper anabranches. The number of channels per cross‐section was 30–40% less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3% to 14%. Copyright © 2012 John Wiley & Sons, Ltd.     

近50 a来新疆区域与天山典型流域极端洪水变化特征及其对气候变化的响应

以年极端洪水超标率来反映区域极端洪水, 分析了新疆区域极端洪水变化; 以年最大洪峰记录分析了天山山区主要河流极端洪水变化规律, 并用14站资料分析了天山山区气候变化特征, 讨论了天山主要河流极端洪水变化对区域气候变化的响应. 结果表明: 受气候变暖影响, 1957-2006年全疆极端洪水呈区域性加重趋势, 尤其南疆区域极端洪水明显加剧, 北疆区域也有加重趋势, 但相对较缓. 全疆及北疆、 南疆在20世纪90年代中期以来都处于洪水高发阶段. 近50 a来, 在新疆区域洪水呈加重趋势的变化背景下, 发源于天山南坡的托什干河和库玛拉克河年最大洪峰流量呈显著增加趋势, 发源于天山北坡的玛纳斯河与乌鲁木齐河年最大洪峰流量虽有增加, 但是变化趋势较缓. 以年最大洪峰流量发生转折年为界, 天山典型流域托什干河、 库玛拉克河、 玛纳斯河和乌鲁木齐河在20世纪90年代(或80年代)以来与前期相比, 呈现出相似的变化特征: 年最大洪峰流量明显增大, 年际间变化更加剧烈, 洪水年更频繁. 以年最大洪峰流量发生转折年份为界, 玛纳斯河、 托什干河和乌鲁木齐河后期的年最大洪峰集中日期较前期推迟2~9 d, 库玛拉克河却提前5 d. 玛纳斯河、 乌鲁木齐河和库玛拉克河后期的集中度较前期增加0.8%~8.3%, 托什干河减小1.1%. 1961-2010年, 新疆天山山区气温明显上升, 升温率为0.34 ℃·(10a)^-1, 1997年以后明显增暖; 天山山区降水显著增加, 增加速率15.6 mm·(10a)^-1, 同时极端降水强度增大、 频数增多. 近50 a来天山主要河流极端洪水变化与区域增温以及天山山区极端降水事件增多等有密切关系.     

Century‐long records reveal slight,ecoregion‐localized changes in Athabasca River flows

Reports of abruptly declining flows of Canada's Athabasca River have prompted concern because this large, free‐flowing river could be representative for northern North America, provides water for the massive Athabasca oil‐sands projects and flows to the extensive and biodiverse Peace–Athabasca, Slave and Mackenzie River deltas. To investigate historic hydrology along the river and its major tributaries, we expanded the time series with interpolations for short data gaps; calculations of annual discharges from early, summer‐only records; and by splicing records across sequential hydrometric gauges. These produced composite, century‐long records (1913–2011) and trend detection with linear Pearson correlation provided similar outcomes to nonparametric Kendall τ‐b tests. These revealed that the mountain and foothills reaches displayed slight increases in winter discharges versus larger declines in summer discharges and consequently declining annual flows (~0.16% per year at Hinton; p < 0.01). Conversely, with contrasting boreal contributions, the Athabasca River at Athabasca displayed no overall trend in monthly or annual flows, but there was correspondence with the Pacific Decadal Oscillation that contributed to a temporary flow decline from 1970 to 2000. These findings from century‐long records contrast with interpretations from numerous shorter‐term studies and emphasize the need for sufficient time series for hydrologic trend analyses. For Northern Hemisphere rivers, the study interval should be at least 80 years to span two Pacific Decadal Oscillation cycles and dampen the influence from phase transitions. Most prior trend analyses considered only a few decades, and this weakens interpretations of the hydrologic consequences of climate change. Copyright © 2014 John Wiley & Sons, Ltd.