River Length Research Articles

Scaling up of tsetse control to eliminate Gambian sleeping sickness in northern Uganda.

Tsetse flies (Glossina) transmit Trypanosoma brucei gambiense which causes Gambian human African trypanosomiasis (gHAT) in Central and West Africa. Several countries use Tiny Targets, comprising insecticide-treated panels of material which attract and kill tsetse, as part of their national programmes to eliminate gHAT. We studied how the scale and arrangement of target deployment affected the efficacy of control. Between 2012 and 2016, Tiny Targets were deployed biannually along the larger rivers of Arua, Maracha, Koboko and Yumbe districts in North West Uganda with the aim of reducing the abundance of tsetse to interrupt transmission. The extent of these deployments increased from ~250 km2 in 2012 to ~1600 km2 in 2015. The impact of Tiny Targets on tsetse populations was assessed by analysing catches of tsetse from a network of monitoring traps; sub-samples of captured tsetse were dissected to estimate their age and infection status. In addition, the condition of 780 targets (~195/district) was assessed for up to six months after deployment. In each district, mean daily catches of tsetse (G. fuscipes fuscipes) from monitoring traps declined significantly by >80% following the deployment of targets. The reduction was apparent for several kilometres on adjacent lengths of the same river but not in other rivers a kilometre or so away. Expansion of the operational area did not always produce higher levels of suppression or detectable change in the age structure or infection rates of the population, perhaps due to the failure to treat the smaller streams and/or invasion from adjacent untreated areas. The median effective life of a Tiny Target was 61 (41.8-80.2, 95% CI) days. Scaling-up of tsetse control reduced the population of tsetse by >80% across the intervention area. Even better control might be achievable by tackling invasion of flies from infested areas within and outside the current intervention area. This might involve deploying more targets, especially along smaller rivers, and extending the effective life of Tiny Targets.

Kinematic reverse flood routing in natural rivers using stage data

In many developing countries, due to economic constraints, a single station on a river reach is often equipped to record flow variables. On the other hand, hydrographs at the upstream sections may also be needed for especially assessing flooded areas. The upstream flow hydrograph prediction is called the reverse flood routing. There are some reverse flood routing pocedures requiring sophisticated methods together with substantial data requirements. This study proposes a new reverse flood routing procedure, based upon the simple kinematic wave (KW) equation, requiring only easily measurable downstream stage data. The KW equation is first averaged along a channel length at a fixed time, t, assuming that channel width is spatially constant, and then the spatially averaged equation is averaged in time, Δt. The temporally averaged terms are approximated as the arithmetical mean of the corresponding terms evaluated at time t and t + Δt. The Chezy roughness equation is employed for flow velocity, and the upstream flow stage hydrograph is assumed be described by a two parameter gamma distribution (Pearson Type III). The spatially averaged mean flow depth and lateral flow are related to the downstream flow stage. The resulting routing equation is thus obtained as a function of only downstream flow stage, meaning that the method mainly requires measurements of downstream flow stage data besides the mean values of channel length, channel width, roughness coefficient and bed slope. The optimal values of the parameters of reverse flood routing are obtained using the genetic algorithm. The calibration of the model is accomplished by using the measured downstream hydrographs. The validation is performed by comparing the model-generated upstream hydrographs against the measured upstream hydrographs. The proposed model is applied to generate upstream hydrographs at four different river reaches of Tiber River, located in central Italy. The length of river reaches varied from 20 to 65 km. Several upstream hydrographs at different stations on this river are generated using the developed method and compared with the observed hydrographs. The method predicts the time to peak with less than 5% error and peak rates with less than 10% error in the short river reaches of 20 km and 31 km. It also predicts the time to peak and peak rate in other two brances of 45 km and 65 km with less than 15% error. The method satisfactorily generates upstream hydrographs, with an overall mean absolute error (MAE) of 42 m3/s.

Spatial Analysis of Liquid Pollutant Potential in Industrial Type UKL-UPL Documents In Jombang Regency

Background: The establishment of new industries is often associated with potential waste to be produced and environmental problems that may arise due to the activities carried out by the industry in the future. One of many environmental problems due to industrial waste is the pollution of water, air, and soil in the area around where the industry is located. The number of industrial types UKL-UPL submissions in Jombang Regency from 2006-2020 is unstable but tend to increase from 2015-2020. Jombang Regency is a downstream area of the Brantas River which its Water Quality Index has decreased from 49.17 in 2015 to 47.68 in 2016.Objectives: The purpose of this study was to analyze spatially the location of the industry that had the potential for liquid pollutants and river distribution in Jombang Regency.Methods: This study uses observational research design with a quantitative descriptive approach with a spatial analysis model. The data used is secondary data, namely the submission data of Jombang Regency UKL UKL document in 2006-2020, coordinate data of the location of the industry, and spatial river data.Results: Industrial establishment plans on Jombang Regency are mostly centered around it’s regency seat. The length of rivers in Jombang tend to be longer in the northen and sourthern sub-districts. There is no significant difference on the location of industrial establishment plan to the nearest river for industries with and without liquid pollutant potentials (0.912 < 0.05).Conclusion: Even thought sub-districts with high industry counts has shorter river length, regular river water quality monitoring is required to be done so that it doesn’t exceed environmental quality standards and cause health problems.

Pollutant transport via sediments in medium-sized meandering rivers: the example of barium in Kupa River (Croatia)

The aim of our study is to expand the world-wide knowledge about pollutant transport in sediments of medium-sized meandering rivers and to explain barium distribution in Kupa River (Croatia), which showed as an ideal “natural laboratory”. Sampling was performed twice at the same places with the time span of 15 years to see the changes in Ba concentrations after that period. Ba was analyzed using ICP-MS method on clay + silt sediment fraction (< 63 µm). Modelling was performed in R environment. After barite mine ceased operation in 1990, Ba is still entering Kupica and Kupa rivers, as karstic underground still contains large amounts of barite waste. Ba concentrations in Kupa River sediments are still increasing consequently along the whole river length, except in Kupica River and first downstream sample in Kupa River. It seems that in this part of the river course erosion exceeded deposition processes. Also, there is an indication of changing the way of underground Ba transport. Erosion and deposition processes lead to formation of peak of Ba concentrations in the lower course of the Kupa River. The most important conclusion is that the peak was formed under one or two flood episodes, when sediment eroded from the upstream locations and was brought and deposited in the lower course of the river. Our modelling predicts that Ba source will not cease during the next 20 years. Additional sampling of river- and ground-water showed that the correlation between Ba in sediment and river water is statistically significant (0.79, p < 0.05). This might be result of Ba dissolution from the sediment and dilution with waters entering from Kupa River tributaries.

Morphometric characteristics of the Alas-Singkil drainage basins

The Alas-Singkil drainage basin is the broadest watershed and an essential ecosystem for maintaining hydrology and ecosystems in the northern Sumatera. This study aims to describe the morphometric and hydrological characteristics of the Singkil watershed. The data sourced from Google Earth, DEM data and the results of team expeditions at the sub-watershed locations. The data analysis is related to the characteristics of the Singkil watershed, which include watershed area, watershed shape, river network, river flow pattern, river flow density, and watershed hydrology. Analysis of hydrological characteristics by calculating the peak of the flood was also carried out. The results showed that the Singkil watershed is a broad watershed with an area of 12027.18 km2. The Alas-Singkil drainage basin consists of 7 sub-watersheds, with the length of the main river reaching 368 km. The order of Singkil watershed reaches 8 orders and consists of 7235 orders 1, 1964 orders 2, 390 orders 3, 92 orders 4, 26 orders 5, 6 orders 6, 4 orders 7. The shape of Alas-Singkil drainage basin is elongated with RC value of 0.16. The level of river branching in the Alas-Singkil watershed is 4.76. The maximum discharge in the Alas-Singkil watershed reaches 59,178 m3/sec.

Mapping riverbed sediment size from Sentinel‐2 satellite data

AbstractA comprehensive understanding of river dynamics requires the grain size distribution of bed sediments and its variation across different temporal and spatial scales. Several techniques are already available for grain size assessment based on field and remotely sensed data. However, the existing methods are only applicable on small spatial scales and on short time scales. Thus, the operational measurement of grain size distribution of riverbed sediments at the catchment scale remains an open problem. A solution could be the use of satellite images as the main imaging platform. However, this would entail retrieving information at sub‐pixel scales.In this study, we propose a new approach to retrieve sub‐pixel scale grain size class information from Copernicus Sentinel‐2 imagery building upon a new image‐based grain size mapping procedure. Three Italian gravel‐bed rivers featuring different morphologies were selected for unmanned aerial vehicle (UAV) acquisitions, field surveys and laboratory analysis meant to serve as ground truth grain size data, ranging from medium sand to coarse gravel. Grain size maps on the river bars were generated in each study site by exploiting image texture measurements, upscaled and co‐registered with Sentinel‐2 data resolution.Relationships between the grain sizes measured and the reflectance values in Sentinel‐2 imagery were analysed using a machine learning framework. Results show statistically significant predictive models (MAE of ±8.34 mm and R2 = 0.92). The trained model was applied on 300 km of the Po River in Italy and allowed us to identify the gravel–sand transition occurring along this river length.Therefore, the approach presented here—based on freely available satellite data calibrated by low‐cost drone‐derived imagery—represents a promising step towards an automated surface mean grain size mapping over long river length, easily repeated through time for monitoring purposes.

First insight into the macroplastic storage in a mountain river: The role of in-river vegetation cover, wood jams and channel morphology

Macroplastic storage in mountain rivers remains unexplored and it is unknown how river morphology and different surface types of river areas modulate this process. Therefore, we sampled macroplastic debris stored on the surface of emergent river areas with different vegetation cover and on wood jams in a channelized, single-thread reach and an unmanaged, multi-thread reach of the Dunajec River in the Polish Carpathians. Total amounts of macroplastic debris retained in these reaches were then estimated on the basis of mean mass of macroplastic deposited on unit area of each surface type and the area of this surface type in a given reach. Exposed river sediments and areas covered with herbaceous vegetation stored significantly lower amounts of macroplastic debris (0.6 and 0.9 g per 1 m2 on average) than wooded islands and wood jams (respectively 6 g and 113 g per 1 m2). The amounts of macroplastic debris stored on wood jams exceeded 19, 129 and 180 times those found on wooded islands, areas covered with herbaceous vegetation and exposed river sediments. Wooded islands and wood jams covering 16.7% and 1.5% of the multi-thread reach stored 43.8% and 41.1%, respectively, of the total amount of macroplastic stored in that reach, whereas these surface types were practically absent in the channelized reach. Consequently, the unmanaged, multi-thread reach, 2.4 times wider than the neighbouring channelized reach, stored 36 times greater amount of macroplastic per 1 km of river length. Our study demonstrated that the storage of macroplastic debris in a mountain river is controlled by channel management style and resultant river morphology, which modulate river hydrodynamics and a longitudinal pattern of the zones of transport and retention of macroplastic conveyed by river flow.

Influence of natural and anthropogenic controls on runoff in the Keriya River, central Tarim Basin, China.

The potential impact of natural factors on the runoff of intermittent rivers and ephemeral streams (IRES) has been largely ignored in the Tarim Basin, China. A representative example is the Keriya River. To quantify the long-term dynamic variations in lower reach surface runoff of IRES, river length, defined as the distance between a selected fix point along the perennial river segment to its dynamic, ephemeral end, was used as an indicator. Using a total of 272 remote sensing images, we digitized and measured the distance (river length) between the center of Yutian County and the river’s end point on each image, and then calculated monthly inter-annual and intra-annual variations in length of the lower Keriya River from 2000 to 2019. Hydrometeorological data were combined with descriptors of anthropogenic disturbances to assess the relative influence of natural factors and anthropogenic disturbances on lower reach river runoff. The results showed that intra-annual variations in river length fluctuated seasonally, with the minimum value occurring in June; two main peaks occurred in March and August. The minimum June value in river length was closely linked to an increase in agricultural water demand and a decrease in upper reach runoff. The August peak in river length was related to the peak values in upper reach runoff and agricultural water demand; upper reach runoff made a significant contribution because the former was about 20% more than the latter in summer. The March peak corresponded to elevated lower reach groundwater levels and to the melting of ice along river channels. Inter-annual variations in river length were due to inter-annual variations in upper reach runoff and middle reach agricultural water use which increased slightly during the study period. Inter-annual variations in frequency and amplitude of the fluctuations in river length were mainly controlled by changes in upper reach runoff. The minimum in river length in 2009 was consistent with the low in upper reach runoff of the Keriya River and other rivers in the Tarim Basin. The most significant factors controlling variations in river length are natural in origin.

Morphometric characterization of the Alto do Ipojuca hydrographic basin

The study of hydrographic basins has supported a series of important decisions for water resources management. Thus, this study aimed to carry out a morphometric characterization of the Alto of Ipojuca Basin addressing the management and integrated planning of water resources. The present study included the Pernambuco municipalities of Alagoinha, Arcoverde, Belo Jardim, Cachoeirinha, Capoeiras, Pesqueira, Poção, Sanharó, São Bento do Una, Sertânia, Tacaimbó and Venturosa, a region corresponding to the Upper Ipojuca region. For morphometric characterization, the Digital Elevation Model (DEM) from the National Institute for Space Research (INPE) was used. The delimitation of the hydrographic basin was carried out using the hydrological model SWAT 1.9, through the QSWAT interface, coupled with the free QGIS software. The geometric parameters obtained use the drainage area, perimeter, compactness coefficient, form factor, elongation ratio and circularity index. The length of the main river, the concentration time, the fluvial hierarchy, the frequency of channels, the drainage density, the hydrographic density, the sinuosity of the main course, the maximum altimetric amplitude of the basin, the mean slope were determined, as well as the roughness index and the relief ratio were also estimated. The basin has an elongated shape, thus favoring flow along the basin and low possibility of flash and sharp floods. In general, the basin has a good trend towards conservation. The study of such parameters emerges as an alternative and a strong support for water resources planning and management , considering the presence of reservoirs within the studied perimeter and water allocation, as rainfall events become increasingly irregular and variable in space and time, due to climate change.

Anthropogenic Intensity-Determined Assembly and Network Stability of Bacterioplankton Communities in the Le'an River.

Bacterioplankton are essential components of riverine ecosystems. However, the mechanisms (deterministic or stochastic processes) and co-occurrence networks by which these communities respond to anthropogenic disturbances are not well understood. Here, we integrated niche-neutrality dynamic balancing and co-occurrence network analysis to investigate the dispersal dynamics of bacterioplankton communities along human activity intensity gradients. Results showed that the lower reaches (where intensity of human activity is high) had an increased composition of bacterioplankton communities which induced strong increases in bacterioplankton diversity. Human activity intensity changes influenced bacterioplankton community assembly via regulation of the deterministic-stochastic balance, with deterministic processes more important as human activity increases. Bacterioplankton molecular ecological network stability and robustness were higher on average in the upper reaches (where there is lower intensity of human activity), but a human activity intensity increase of about 10%/10% can reduce co-occurrence network stability of bacterioplankton communities by an average of 0.62%/0.42% in the dry and wet season, respectively. In addition, water chemistry (especially NO3–-N and Cl–) contributed more to explaining community assembly (especially the composition) than geographic distance and land use in the dry season, while the bacterioplankton community (especially the bacterioplankton network) was more influenced by distance (especially the length of rivers and dendritic streams) and land use (especially forest regions) in the wet season. Our research provides a new perspective of community assembly in rivers and important insights into future research on environmental monitoring and classified management of aquatic ecosystems under the influence of human activity.

River adjustments, geomorphic sensitivity and management implications in the Waipā catchment, Aotearoa New Zealand

Assessment of River Styles, accompanied by time series analysis of historic imagery and geomorphic change detection techniques are used to explain the capacity for river adjustment (geomorphic sensitivity) in relation to the distribution of stream power along 3000 km of channels (3rd Strahler order and greater) to better inform management initiatives in the Waipā catchment, the largest tributary of the Waikato River on the North Island of Aotearoa, New Zealand. Unlike most dynamically adjusting physical landscapes of Aotearoa, most reaches within the Waipā catchment are resistant to geomorphic change. Only 3% of the studied river length has experienced significant planform adjustment since the 1950s and is considered highly sensitive to adjustment. Contemporary alluvial dynamism is largely restricted to gravel bed reaches in high energy rivers within the piedmont zone. The capacity for lateral adjustment in headwater stream courses is restricted by the imprint of past volcanic activity. Further downstream capacity is also limited because of terrace constraints as a result of post-glacial base-level fall, and the entrenchment of the Waikato Fan. Anthropogenic modifications in the catchment include drained wetlands, straightened channels, reinforced banks and emplaced artificial levees (stopbanks) in the few reaches that were prone to adjustment. Highlighting geomorphologically-sensitive reaches at the catchment-scale helps to better prioritise rehabilitation efforts and to support the design and implementation of proactive management plans.

The legacy of over a century of introductions: Spread debt of rainbow trout (Oncorhynchus mykiss) in Mpumalanga Province, South Africa

AbstractFor over a century, rainbow trout (Oncorhynchus mykiss) has been widely introduced into lakes and rivers in South Africa to create and enhance sport‐fishing opportunities. Despite its long history of introduction, naturalized populations of rainbow trout are still localized to a few areas with suitable habitats and climate. This study assessed the spread debt (i.e., the increase in area invaded by invasive species over time) of rainbow trout in Mpumalanga Province, South Africa to highlight areas with known introductions, the extent of the invasion, and to identify areas that are suitable for establishment but are still invasion‐free. The total river length that was predicted as suitable for rainbow trout under current climate was about ca. 3,500 km in an extension of about ca. 15,000 km. Current occupancy (river length predicted as suitable with known rainbow trout occurrence records) was ca. 1,220 km (35%) and the invasion debt was therefore estimated as 65%. While these data infer a large invasion debt, they are confounded by a lack of knowledge on sampling effort and verified true absence and should therefore be recognized as an estimate. In addition, the extent of the suitable area varied under different climate change scenarios where it was projected to decrease under RCP 4.5 scenarios and increase under the RCP 8.5 scenarios. This study demonstrates some of the difficulties of quantifying the potential future extent and impacts of biological invasions and how the invasion debt concept can be applied to provide an important link between invasion biology, management, and policy.

A New Method for Long-Term River Discharge Estimation of Small- and Medium-Scale Rivers by Using Multisource Remote Sensing and RSHS: Application and Validation

River discharge is an important hydrological parameter of river water resources. Especially in small- and medium-scale rivers, data deficiency is the biggest problem for studies of river discharge. In recent years, remote sensing has become a rapid and convenient method to estimate river discharge. However, remote sensing images still have some difficulty generating continuous long-term river discharge. To address this problem, we developed a new method coupling the remote sensing hydrology station method (RSHS) with statistical regression downscaling, using data from optical satellites (Landsat-8, Sentinel-2), radar satellites (Sentinel-1), and un-manned aerial vehicles (UAVs). We applied this method to monitor monthly river discharge for small- and medium-scale rivers from 2016 to 2020 on Yunnan-Guizhou Plateau and evaluated the accuracy of the results. The results show that (1) by applying the newly constructed method, the water body continuity index obtained by Landsat-8 increased by 7% and the average river length percentage in the channel reached 90.7%, a 40% increase; (2) there were only 10 river flow data points, on average, in the 5-year period obtained before this method was applied; after this method was applied, more than 50 river flow data points could be obtained, on average, extending the quantity of data fivefold; in addition, improper extreme values could also be avoided; (3) with better continuity of water body distribution, the images provided steadier river widths. The relative error of daily flow estimation from Landsat-8 images was reduced by 60% and the mean percentage error was reduced by one-fourth. The relative error of the multisource remote sensing composited flow was reduced by 37% with a reduction in the mean percentage error of over a half; (4) in addition, we found that when the threshold difference between water bodies and land in remote sensing images is more than 0.2, the impact of water body recognition error on flow accuracy can be ignored. This method helps to overcome the absence of remote sensing methods for the long-term estimation of flow series in small- and medium-scale rivers, improves the accuracy of remote sensing methods for calculating flow, and provides ideas for regional water resource management and utilization.

Analysis of Flood Peak Discharge Based on Watershed Shape Factors

Regression analysis can develop unit hydrograph modeling by approaching the peak discharge (Qp) and time to peak (Tp) parameters. The main aim of this study is to design a model of peak discharge based on watershed shape factors. The watersheds used in this study are Bontojai Watershed, Jonggoa Watershed, Kampili Watershed, Maccini Sombala Watershed, and Jenelata Watershed, which have slopes criteria below 10% and have complete recorded data of Automatic Water Level Recorder (AWLR) and Automatic Rainfall Recorder (ARR). The validation results of corrected peak discharge data produce Root Mean Squared Error (RMSE). Then, the peak discharge model was conducted by regression analysis and validated with observed unit hydrographs. The results of this study indicate that the coefficient of determination R2 is 0.963. It means that the independent variable (x), namely the area of the watershed, the length of the main river, and the shape factor of the watershed, influences the peak discharge (Qp) of 96.3%

OPTIMIZATION STUDY OF GATE OPERATION RULE IN CIAWI DAM AS FLOOD CONTROL FUNCTION

The purpose of this research is to find out the effectiveness of operating gate on the design of flood routing and provide an alternative outlet operation gate for maximum flood reduction. The location of the research area is the Ciawi Dam watershed with an area of ​​88.50 km2, a river length of ±16.70 km and an average river slope of 5.60%. This research data is based on climatological data, low discharge data, flood hydrograph, and dam and reservoir engineering data. In addition, there are supporting data to perform calculations and analyzes, such as flood discharge data, elevation curve – reservoir volume and layout of the dam and its complementary buildings, existing operating patterns, and regional socio-economic data studies. The method used is to calculate flood routing of the capital flow curve at the outlet operation gate. The simulation is carried out using a design flood hydrograph so that optimal flood reduction can be determined by the outlet operation gate. Based on the results of the maximum reduction in the design of the reservoir operation dam design without utilizing the conduit gate as a flood control function, the researchers optimized the door operation pattern to increase the flood reduction capacity (optimization) of the Ciawi Dam. The result of the calculation and analysis is that the flood return period (Q25 th) is able to reduce flooding by 54.64%; flood return period (Q50 yr.) is able to reduce flooding by 45.21%; flood return period (Q100 yr.) is able to reduce flooding by 38.06%; flood return period (Q500 yr.) is able to reduce flooding by 38.50%; and the flood return period (Q1000 yr.) was able to reduce flooding by 33.22%. So, it can be concluded that by utilizing the bottom outlet gate as a flood discharge regulation, the benefits obtained are 42.27% (at Q 25 yrs.) from the pattern of dam operation without gate regulation.

Health Assessment for Mountainous Rivers Based on Dominant Functions in the Huaijiu River, Beijing, China.

Dominant functions usually vary greatly in different reaches of mountainous rivers and are influenced by different adjacent land uses. Assessing river health based on dominant functions is of great practical value to river management. To reveal the health status of different reaches in Beijing's northern mountainous rivers, 60 investigated plots (river length 38.1 km) were surveyed in 2016 in the Huaijiu River, which is a typical mountainous river in northern Beijing, and a hierarchy-comprehensive analysis method was employed. Based on the degree of human influences, the Huaijiu River could be classified into six types, including natural reaches, near-natural reaches, artificial bank plant reaches, artificial bank ornamental plant reaches, artificial bank sparse plant dry-stone reaches and artificial bank masonry reaches. The river health assessment index system was established based on flood control, landscape, hydrology and water quality, and ecological functions. The analytic hierarchy process (AHP) was used to determine the weights of the function layer and indicator layer. The assessment results showed that healthy, subhealthy, slightly damaged, damaged and severely damaged plots accounted for 20.0%, 26.7%, 26.7%, 15.0% and 11.6% of the total plots, respectively. In summary, all plots in natural reaches, artificial bank plant reaches and artificial bank ornamental plant reaches were either healthy, subhealthy or slightly damaged. Plots in artificial bank masonry reaches were either subhealthy, slightly damaged, damaged or severely damaged, accounting for 9.1%, 27.3%, 27.3% and 36.4% of the total plots, respectively. The study proposed a method to assess mountainous river health based on dominant functions, which is a multiobjective approach and is not based solely on natural river functions. The assessment method is appropriate for the socioeconomic development and management of river basins.

Effects of road and river networks on sediment connectivity in mountainous watersheds

Road and river networks in mountainous watersheds play an important role in transporting eroded sediments. However, the underlying transport mechanisms remain poorly understood, particularly in terms of how alterations to flow paths caused by road and river networks influence sediment connectivity. Therefore, using data from the Dongshuanghe (DSH) watershed in the Dabie Mountain in Central China, this study investigated the spatial relationships between road and river networks, analyzed the effects of road and river networks on the spatial distribution of sediment connectivity, and determined the primary factors influencing sediment connectivity. The primary factors were identified using the index of connectivity (IC), buffer analysis, a random forest (RF) model, and a geographical detector model (GDM). The results indicated that road and river networks were spatially closely associated: closer to rivers, the density of high-grade roads increased, while farther from road-river crossings, the length and density of rivers and high-grade roads decreased. Both road and river networks affected the IC. In particular, for permanent drainage lines or local sinks, the average value of ICR (i.e., IC affected by road networks, −0.97) was higher than that of IC (−2.17). Thus, values of ICR decreased substantially with increasing distance to the closest roads (R2 = 0.73). However, beyond a threshold of 150 m, the effect of roads on ICR gradually diminished. In addition, the structural characteristics of road networks, particularly slope (Road_S), had greater explanatory power for spatial variation in the ICR. In conclusion, compared to the river networks, the effect of road networks on ICR was more important, which was not only reflected in the spatial distribution of ICR, but also in the factors influencing ICR.

Effect of Urbanization on the River Network Structure in Zhengzhou City, China.

Hydrological problems, such as flood disasters, can be caused by the influence of urbanization on river network structures in plain areas. Taking the main urban region of Zhengzhou city as the research area, based on six remote sensing images from 1992 to 2015, the modified normalized difference water index method and a land-use transfer matrix were used to reconstruct river network data to study the temporal and spatial changes in the river system. In addition, the analytic hierarchy process and the entropy weight method were used to construct pattern indexes of the river system to quantitatively evaluate the inner relationship between the urbanization process and the river network structure in the plain area. The results showed that the percentages of arable land, forest and grassland, water, and unused land in Zhengzhou that was transferred to construction land from 1992 to 2015 were 59.10%, 51.05%, 29.83%, and 58.76%, respectively. In the past 34 years, the morphological indices, structural indices, and connectivity indices of the river system experienced a trend of high to low, and then increased, with the structural indices being significantly correlated with construction land use (p < 0.05). The regression equation R2 between urbanization level and river length, water area, river network density, water surface rate, connection rate, and connectivity ranged from 0.677 to 0.966, which could well reflect the response relationship between urbanization and the river network. In addition, the outflow was greater than the inflow, which has destroyed the natural structure of the channel.

Relationships between erosion rates and physiographic factors of drainage basins through a regression analysis: The case of Tahiti Nui Island

Tahiti Nui is a quiescent tropical volcanic island (French Polynesia) characterized by an intense erosion (up to 0.25 km3·kyr−1 over the last 1 Ma) that resulted in 27 main drainage basins radially distributed around a central depression. Those basins are characterized by different erosion rates (from 0.07 to 24.6 10−2 km3·kyr−1), ages (from 469 to 892 ka), micro-climate set-ups and other landform factors. In this study, we assess, in terms of explicative power, possible links between the erosion rates and relevant physiographic factors, through a regression analysis obeying the parsimony principle. The best regression models include, in decreasing order of importance, the following factors: the size (Planar Area or Maximal River Length) and/or the height (Maximal Altitude); the planar shape (Shape Factor or Relative Width); the inclination (Main Longitudinal Slope, Mean Slope, Maximum Altitude or Depth) and the mean precipitation (Average Annual Rainfall). The Erosion Duration and the positions along the North-South and East-West directions, which were used to highlight a possible effect of the winds, did not show significant effect on the erosion rates. In all the best fitting models, the greatest weight was associated with the size or the height factors, revealing that the highest erosion rates are the ones measured on the largest and/or highest basins. The best model is based on five physiographic factors per basin, in order of importance: Planar Area, Relative Width, Maximum Altitude, Main Longitudinal Slope and Average Annual Rainfall. The Planar Area factor seems to be the most relevant parameter since it explains by itself the largest part of the erosion rates. Finally, the role of average annual rainfall is not consistent between the regression models. This suggests that a more suitable physiographic factor to constrain the effect of precipitations on erosion rates must be considered, probably linked to the temporal climate variability as well as the frequency of cyclone-driven rainfall. Besides, the weight of the Average Annual Rainfall factor was generally positive and small in most regression models, synonymous of a minor role.

A new index to quantify longitudinal river fragmentation: Conservation and management implications

The proliferation of river infrastructure projects has altered aquatic longitudinal connectivity, posing a growing threat to riverine biodiversity and ecosystem processes worldwide. Effective methods to quantify loss of river connectivity across spatiotemporal scales and in data-limited landscapes are important to understand and inform basin-wide conservation and development planning. Here we introduce a Catchment Area-based Fragmentation Index (CAFI) and its derivative, the Catchment Area- and Rainfall-based Fragmentation Index (CARFI) as new metrics to quantify river fragmentation. These indices use catchment area as a proxy for riverine habitat availability, avoiding the drawbacks of existing metrics that rely on river length and associated derivatives. CAFI/CARFI can be computed across spatiotemporal scales, incorporate barrier passability values, assesses the cumulative impact of multiple barriers, and be applied even in data-limited environments.We first applied CAFI and CARFI to a simulated network to illustrate their properties with respect to the number and location of barriers and compared these results to the widely applied Dendritic Connectivity Index (DCI). While all indices varied with barrier addition, CAFI and CARFI were more sensitive to both barrier number and location. Next, we illustrated the utility of CAFI and CARFI through case studies in two contrasting settings: the Klamath River in California, where dam building has ceased (and dam removals are being considered) and the Netravathi River in India, where dam building is ongoing, with 65 dams proposed for future development. Results indicate that CAFI and CARFI can effectively quantify trends in fragmentation across spatial scales and temporal scenarios of dam development (i.e. descriptive applications) and can aid the prioritization of sites for dam removal, restoration, or conservation (i.e. prescriptive applications). Overall, these indices can quantify the impacts of individual dams and assess a range of development scenarios to inform basin-wide conservation and development planning.