The measurement of river bank erosion and lateral channel change: A review

A detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change. The techniques are classified according to the time scales involved (long, intermediate and short) and each is discussed with respect to accuracy and repeatability. The methods covered include sedimentological evidence, botanical evidence, historical sources, planimetric resurvey, repeated cross-profiling, erosion pins and terrestrial photogrammetry. Prospects for future developments are also discussed.     

Long-term evolution of meandering channel planforms in response to the mean annual flow and width-depth ratio

A depth-averaged linearized meander evolution model was used to numerically evaluate the spatiotem-poral evolution of the meandering channel centerline in the plane at various mean annual flows and width-depth ratios for capturing the overall average trend of the meandering channel planform.This analysis was done to better understand the consistent responses of the river morphology to possible future tectonic and climatic changes.The computational cases included an idealized sine-generated meandering channel with a moderate maximum deflection angle and a typical natural meander for the Jiyun River in China.The study results showed phased development and response characteristics of the meandering channel centerline(to the mean annual flow),along with increases in the specified mean annual width(B)-depth(H)ratio(represented by B/H).First,the spatial meander straightening trend over time weakened during Phase 1(B/H ≤ 16.5)and gradually changed to a meander developing trend during Phase 2(16.5＜B/H ≤ 27)with an overall insensitivity to the flow magnitude.Second,starting from the downstream tail during Phase 3(27＜B/H ≤ 28.9),the symmetric development form along the transverse direction(perpendicular to the mean flow direction)was disrupted,while flow effects were highlighted when the mean annual B/H exceeded 28.Finally,an obvious onset and jump process of the channel sensitivity in response to flow occurred during Phase 4(28.9＜B/H ≤ 29.5).These event characteristics are very similar to the transition from laminar to turbulent flow in fluid mechanics.This study provides insights for more in-depth exploration of meandering mechanisms and technical support for effective river management.     

The influence of bank strength on channel geometry: an integrated analysis of some observations

Bank strength exerts a significant influence on river channel geometry, but quantification of this relationship has been limited to only a few specific circumstances. This is due to both the complex nature of bank strength and the difficulty in incorporating its influence in river channel geometry relations. In order to undertake an integrated analysis of wide-ranging field observations, this study applies a recently developed multivariate model of channel geometry. When the banks of a number of laterally stable streams are categorized on the basis of the bank sediment and vegetation, the multivariate model yields numerical indices of bank strength. Within the range of the data analysed, bank strength can produce a three-fold change in channel width and a two-fold change in depth corresponding to about a 1·6-fold change in cross-sectional area. © 1998 John Wiley & Sons, Ltd.     

Impact of land-use change on hydrological processes in the Maying River basin, China

Since the 1960s, dramatic changes have taken place in land-use patterns characterized by the persistent expansion of cultivated land and a continuous decrease in natural woodland and grassland in the arid inland river basins of China. It is very important to assess the effects of such land-use changes on the hydrological processes so vital for water resource management and sustainable development on the catchment scale. The Maying River catchment, a typical arid inland watershed located in the middle of the Hexi Corridor in northwest China, was the site chosen to investigate the hydrological responses to land-use changes. The annual runoff, base flow, maximum peak flow, and typical seasonal runoff in both spring and autumn flood periods were selected as the variables in the hydrological processes. Statistical-trend analysis and curvilinear regression were utilized to detect the trends in hydrological variables while eliminating the climatic influence. The relationship between cultivated land-use and hydrological variables was analyzed based on four periods of land-use variation data collected since 1965. A runoff model was established composed of two factors, i.e., cultivated land use and precipitation. The impact of land use changes, especially in the large ar- eas of upstream woodland and grassland turned into cultivated lands since 1967, has resulted in a mean annual runoff decrease of 28.12%, a base flow decline of 35.32%, a drop in the maximum peak discharge of 35.77%, and mean discharge decreases in spring and autumn of 36.05% and 24.87% respectively, of which the contribution of cultivated land expansion to the influence of annual runoff amounts to 77%-80%, with the contribution to the influence of spring discharge being 73%-81%, and that to the influence of base flow reaching 62%-65%. Thus, a rational regulation policy of land use patterns is vitally important to the sustainable use of water resources and the proper development of the entire catchment.     

Abrupt change of runoff and its major driving factors in Haihe River Catchment, China

Runoff in Haihe River Catchment of China is steadily declining due to climate change and human activity. Determining abrupt changes in runoff could enhance identification of the main driving factors for the sudden changes. In this study, the sequential Mann–Kendall test analysis is used to determine abrupt changes in runoff in eight sub-catchments of Haihe River Catchment, while trend analysis via the traditional Mann–Kendall test for the period 1960–1999 is used to identify the basic trend of precipitation and runoff. The results suggest an insignificant change in precipitation and a significant decline in runoff in five of the eight sub-catchments. For most of the sub-catchments, abrupt changes in runoff occurred in 1978–1985. Through correlation comparisons for precipitation and runoff for the periods prior to and after abrupt runoff changes, human activity, rather than climatic change, is identified as the main driving factor of runoff decline. It is also noted that abrupt decline in runoff was actually at the beginning of China’s 1978–1985 land reform. Given that the land reform motivated farmers to productively manage their reallocated lands, agricultural water use therefore increased. Hence percent agricultural land is analyzed in relation to land use/cover pattern for the late 1970s and early 1980s. The analysis shows that when cultivated farmland exceeds 25% of a sub-catchment area, an abrupt decline in runoff occurs. It is therefore concluded that high percent agricultural land and related agricultural water use are the most probable driving factors of runoff decline in the catchment.     

Natural flood management,land use and climate change trade-offs: the case of Tarland catchment,Scotland

A distributed hydrological model (WaSiM-ETH) was applied to a mesoscale catchment to investigate natural flood management as a nonstructural approach to tackle flood risks from climate change. Peak flows were modelled using climate projections (UKCP09) combined with afforestation-based land-use change options. A significant increase in peak flows was modelled from climate change. Afforestation could reduce some of the increased flow, with greatest benefit from coniferous afforestation, especially replacing lowland farmland. Nevertheless, large-scale woodland expansion was required to maintain peak flows similar to present and beneficial effects were significantly reduced for larger “winter-type” extreme floods. Afforestation was also modelled to increase low-flow risks. Land-use scenarios showed catchment-scale trade-offs across multiple objectives meant “optimal” flood risk solutions were unlikely, especially for afforestation replacing lowland farmland. Hence, combined structural/nonstructural measures may be required in such situations, with integrated catchment management to synergize multiple objectives.     

Channel change and the significance of floodplain stratigraphy: 1990 flood event,lower river Tay,Scotland

During February 1990 a flood event on the River Tay with an estimated recurrence interval of 70 years in its lower reaches caused extensive flooding and geomorphological change. The most extensive area of flooding and dramatic geomorphological change, the erosion of two new channels across the floodplain, was in the vicinity of the village of Caputh, Perthshire. The location of the eroded channels relates to the position of former river courses, identifiable by depressions in the floodplain surface and floodplain stratigraphy. The lower floodplain surface elevation and occurrence of gravel and sand deposits along the line of the former river courses caused the area to be more vulnerable to erosion and controlled the morphology of the eroded channels.     

Combined effect of climate change and human activities on the hydrological processes of an urban river: case study of the Xiaoqing River,China

ABSTRACT

The aim of this study is to reveal statistical characteristics and exceedance probability of discharge under the combined effect of climate change and human activities. The study is conducted in the Xiaoqing River in Jinan, China, based on data of discharge, land-use types and precipitation from the period 1970–2016. A multivariate joint probability distribution of the data is established to test the univariable, bivariable and trivariable change points. These are then used to calculate and analyse the risk probability of discharge exceeding the specific values under different conditions of precipitation and land-use type. The results show that the change point calculated by trivariate joint distribution can reduce the disturbance of the change point obtained with the univariable or bivariable approach and reflect the changes of various factors in the hydrological processes more objectively. When the land-use type is taken into consideration, the trivariate distribution can reflect the variation of hydrological processes more reasonably.     

Assessment and evaluation of potential climate change impact on monsoon flows using machine learning technique over Wainganga River basin,India

In this study, classification- and regression-based statistical downscaling is used to project the monthly monsoon streamflow over the Wainganga basin, India, using 40 global climate model (GCM) outputs and four representative concentration pathways (RCP) scenarios. Support vector machine (SVM) and relevance vector machine (RVM) are considered to perform downscaling. The RVM outperforms SVM and is used to simulate future projections of monsoon flows for different periods. In addition, variability in water availability with uncertainty and change point (CP) detection are accomplished by flow–duration curve and Bayesian analysis, respectively. It is observed from the results that the upper extremes of monsoon flows are highly sensitive to increases in temperature and show a continuous decreasing trend. Medium and low flows are increasing in future projections for all the scenarios, and high uncertainty is noticed in the case of low flows. An early CP is detected in the case of high emissions scenarios.     

Evolution of the Yellow River delta,China: Impacts of channel avulsion and progradation

The evolution of the Yellow River delta is characterized by heavy sediment load,rapid seaward migration,frequent avulsions,and intense anthropogenic disturbances.Evolution of the delta channel following avulsions is very complex and has not yet been thoroughly understood.In the research presented by this paper,we conducted comprehensive analyses of the changes in the water stages,slopes,longitudinal profiles,and the erosion and deposition in the Yellow River delta channels during a time period of over five decades.Results showed that,following each avulsion,channels migrated seaward at decaying rates and the slopes at the downstream of the avulsion point decreased exponentially with time and completed its major adjustment within about four to five years.A generalized geometric model was proposed to describe the changes in the longitudinal profiles of the delta channels.A calculation method to determine the characteristic water stages at the delta was proposed based on the geometric model and the delayed response model for the morphological responses of fluvial rivers to perturbations.Water stages corresponding to a discharge of 3000 m3/s at Lijin and Xihekou during 1954 through 2012 were calculated by using the proposed method.The proposed method may be used to predict the evolution of the delta channels in response to artificial avulsions at the Yellow River delta in the future.     

Bootstrap Pettitt test for detecting change points in hydroclimatological data: case study of Itaipu Hydroelectric Plant,Brazil

ABSTRACT

The Pettitt test is widely used in climate change and hydrological analyses. However, studies show difficulties of this test in detecting change points, especially in small samples. This study presents a bootstrap application of the Pettitt test, and compares it numerically with the classical Pettitt test by an extensive Monte Carlo simulation. The proposed test outperforms the classical test in all simulated scenarios. An application of the tests is conducted on the historical series of naturalized flows of the Itaipu Hydroelectric Plant in Brazil, for which several studies have shown a change point in the 1970s. When the series is split into shorter sub-series, to simulate actual situations of small samples, the proposed test is more powerful than the classical Pettitt test in detecting the change point. The proposed test can be an important tool for detecting abrupt changes in water availability, in support of hydroclimatological resources decision making.     

Vertical zonality of the water cycle and the impact of land-use change on runoff in the Qingshui River Basin of Wutai Mountain,China

ABSTRACT

Hydrological processes in hilly watersheds are significantly affected by variations in elevation; however, the hydrological functions of different vertical vegetation belts, have rarely been reported. The distributed hydrological model WEP-L (Water and Energy transfer Process in Large river basins) was applied to analyse vertical variations in the hydrological processes of Qingshui River basin (QRB), Wutai Mountain (altitude: 3058 m a.s.l.), China. The results show that the highest ratio of evapotranspiration to precipitation occurs at 1800 m a.s.l. Below 1800 m, evapotranspiration is mainly controlled by precipitation, and in regions above1800 m it is controlled by energy. The runoff coefficients for different vertical vegetation belts may be ranked as follows: farmland > grassland > subalpine meadow > evergreen coniferous shrub forest > deciduous broad-leaved forest. Grassland is the largest runoff production area, contributing approximately 39.10% to the annual water yield of the QRB. The runoff from forested land decreased to a greater extent than the grassland runoff. Increasing forest cover may increase evapotranspiration and reduce runoff. These results are important, not only for further understanding of the hydrological mechanisms in this basin, but also for implementing the sustainable management of water resources and ecosystems in other mountainous regions.     

Climate change inferred from analysis of borehole temperatures: First results from Alberta Basin,Canada

High quality temperature measurements have been made to depths of 30 to 220 m at 42 sites in 62 observational hydrogeological wells in Alberta. The temperature profiles commonly show near-surface inversions with a minimum temperature at depths of 30 to 50 m. Thermal modelling suggests a surface temperature history with warming reaching 2°C over the past 30 to 60 years. Recent climate warming evident from the analysis of the air temperature data in the region seems to provide at least a partial explanation of the increased ground temperatures. A sudden increase of the surface ground temperature caused by land clearing may be the other explanation, although modelling of such a sudden increase can only explain the observed temperature-depth data if the onset of such warming is 20–30 years old, which is in disagreement with the history of land development in the studied area. The effect of near-surface inversions of the temperature profiles also has been observed in the forested areas. The above support the climate based effect. The superposition of the climatic effect and man-made activity effect upon the ground warming is a very complicated process calling for considerably more research.     

Attribution of runoff change in the alpine basin: a case study of the Heihe Upstream Basin,China

Quantifying the relative contributions of different factors to runoff change is helpful for basin management, especially in the context of climate change and anthropogenic activities. The effect of snow change on runoff is seldom evaluated. We attribute the runoff change in the Heihe Upstream Basin (HUB), an alpine basin in China, using two approaches: a snowmelt-based water balance model and the Budyko framework. Results from these approaches show good consistency. Precipitation accounts for 58% of the increasing runoff. The contribution of land-cover change seems unremarkable for the HUB as a whole, where land-cover change has a major effect on runoff in each sub-basin, but its positive effect on increasing runoff in sub-basins 1 and 3 is offset by the negative effect in sub-basin 2. Snow change plays an essential role in each sub-basin, with a contribution rate of around 30%. The impact of potential evapotranspiration is almost negligible.

EDITOR D. Koutsoyiannis

ASSOCIATE EDITOR S. Huang     

Thermal‐infrared remote sensing of surface water–groundwater exchanges in a restored anastomosing channel (Upper Rhine River,France)

Ecohydrological processes are a key element to consider in functional river restorations. In the framework of a LIFE+ European restoration program, we have investigated the potential for airborne thermal‐infrared remote sensing to map surface water–groundwater exchanges and to identify their driving factors. We focused our attention on anastomosing channels on an artificial island of the Upper Rhine River (Rohrschollen), where a new channel was excavated from the floodplain to reconnect an older channel in its upstream part. These hydraulic engineering works led to an increased inflow from the Rhine Canal. Here, we propose an original data treatment chain to (a) georeference the thermal‐infrared images in geographic information system based on visible images, (b) detect and correct data errors, and (c) identify and locate thermal anomalies attributed to groundwater inputs and hyporheic upwellings. Our results, which have been compared to morpho‐sedimentary data, show that groundwater upwelling in the new channel is controlled by riffle–pool sequences and bars. This channel is characterized by large bedload transport and morphodynamic activity, forming riffles and bars. In the old channel, where riffle–pool sequences no longer exist, due to impacts of engineering works and insufficient morphodynamic effects of the restoration, thermal anomalies appeared to be less pronounced. Groundwater inputs seem to be controlled by former gravel bars outcropping on the banks, as well as by local thinning of the low‐permeability clogging layer on the channel bed.     

Responses of streamflow to climate change in the northern slope of Tianshan Mountains in Xinjiang: A case study of the Toutun River basin

A case study on the responses of streamflow to climate change in the Toutun River basin was carried out based on data analysis of streamflow, precipitation, and temperatures during the past 50 years.Temporal series of the streamflow change in the Toutun River basin was analyzed and tested using the Mann-Kendall nonparametric test. Results revealed that the annual runoff of the Toutun River had been in a monotonic decreasing trend for the past 50 years. Compared with the 1950s and 1960s, the annual runoff in the 1990s decreased by 4.0×105 m3 and 7.2×105 m3. The precipitation did not show monotonic trend during the past 50 years, but the annual temperature increased by 1.12℃ since the 1950s. Further data analysis indicated that the monthly runoff of the Toutun River decreased significantly from August to October, with precipitation displaying the similar pattern of seasonal change. Analysis suggests that the reduction of streamflow in the Toutun River basin is possibly caused by the seasonal change of precipitation, especially the precipitation reduction in summer, and temperature increases.     

Spatio-temporal variability of streamflow in the Yellow River: possible causes and implications

Abstract

The water shortage in the Yellow River, China, has been aggravated by rapid population growth and global climate changes. To identify the characteristics of streamflow change in the Yellow River, approximately 50 years of natural and observed streamflow data from 23 hydrological stations were examined. The Mann-Kendall and Pettitt tests were used to detect trends and abrupt change points. The results show that both the natural and the observed streamflow in the Yellow River basin present downward trends from 1956 to 2008, and the decreasing rate of observed streamflow is generally faster than that of the natural streamflow. Larger drainage areas have higher declining rates, and the declining trends are intensified downstream within the mainstream. The possibility of abrupt changes in observed streamflow is higher than in natural streamflow, and streamflow series in the mainstream are more likely to change abruptly than those in the tributaries. In the mainstream, all the significant abrupt changes appear in the middle and latter half of the 1980s, but the abrupt changes occur somewhat earlier for observed streamflow than for natural streamflow. The significant abrupt change for the observed streamflow in the tributaries is almost isochronous with the natural streamflow and occurs from the 1970s to 1990s. It is implied that the slight reduction in precipitation is not the only direct reason for the streamflow variation. Other than the effects of climate change, land-use and land-cover changes are the main reasons for the natural streamflow change. Therefore, the increasing net water diversion by humans is responsible for the observed streamflow change. It is estimated that the influence of human activity on the declining streamflow is enhanced over time.

Editor Z.W. Kundzewicz

Citation Miao, C.Y., Shi, W., Chen, X.H., and Yang, L., 2012 Miao, C.Y., Yang, L. and Chen, X.H. 2012. The vegetation cover dynamics (1982–2006) in different erosion regions of the Yellow River basin, China. Land Degradation and Development, 23(1): 62–71. [Crossref], [Web of Science ®] , [Google Scholar]. Spatio-temporal variability of streamflow in the Yellow River: possible causes and implications. Hydrological Sciences Journal, 57 (7), 1355–1367.     

Analysis of uncertainties in the hydrological response of a model‐based climate change impact assessment in a subcatchment of the Spree River,Germany

Climate change impact assessments form the basis for the development of suitable climate change adaptation strategies. For this purpose, ensembles consisting of stepwise coupled models are generally used [emission scenario → global circulation model → downscaling approach (DA) → bias correction → impact model (hydrological model)], in which every item is affected by considerable uncertainty. The aim of the current study is (1) to analyse the uncertainty related to the choice of the DA as well as the hydrological model and its parameterization and (2) to evaluate the vulnerability of the studied catchment, a subcatchment of the highly anthropogenically impacted Spree River catchment, to hydrological change. Four different DAs are used to drive four different model configurations of two conceptually different hydrological models (Water Balance Simulation Model developed at ETH Zürich and HBV‐light). In total, 452 simulations are carried out. The results show that all simulations compute an increase in air temperature and potential evapotranspiration. For precipitation, runoff and actual evapotranspiration, opposing trends are computed depending on the DA used to drive the hydrological models. Overall, the largest source of uncertainty can be attributed to the choice of the DA, especially regarding whether it is statistical or dynamical. The choice of the hydrological model and its parameterization is of less importance when long‐term mean annual changes are compared. The large bandwidth at the end of the modelling chain may exacerbate the formulation of suitable climate change adaption strategies on the regional scale. Copyright © 2013 John Wiley & Sons, Ltd.     

Decadal changes in distribution and frequency of wood in a free meandering river,the Ain River,France

This study examined the temporal dynamics and longitudinal distribution of wood over a multi‐decadal timescale at the river reach scale (36 km) and a meander bend scale (300–600 m) in the Ain River, a large gravel‐bed river flowing through a forested corridor, and adjusting to regulation and floodplain land‐use change. At the 36 km scale, more wood was recruited by bank erosion in 1991–2000 than since the 1950s. The longitudinal distribution of accumulations was similar between 1989 and 1999, but in both years individual pieces occurred homogeneously throughout the reach, while jam distribution was localized, associated with large concave banks. A relationship between the mean number of pieces and the volume recruited by bank erosion (r² = 0·97) indicated a spatial relationship between areas of wood production and storage. Wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends. Sinuosity was related to wood mass recruited by bank erosion during the previous decade (r² = 0·73) and both of these parameters were correlated to the mean mass of wood/plot (r² = 0·98 and 0·69 respectively), appearing to control wood storage and delivery at the bend scale. This suggests a local origin of wood stored in channel, not input from upstream trapped by preferential sites. The increase in wood since 1950 is a response to floodplain afforestation, to a change from braided to meandering channel pattern in response to regulation, and to recent large floods. We observed temporal stability of supply and depositional sectors over a decade (on a reach scale). Meander bends were major storage sites, trapping wood with concave banks, also delivering wood. These results, and the link between sinuosity and wood frequency, establish geomorphology as a dominant wood storage and recruitment control in large gravel‐bed rivers. Copyright © 2007 John Wiley & Sons, Ltd.