Contributing Catchment Area Research Articles

The Role of Stream Restoration in Mitigating Sediment and Phosphorous Loads in Urbanizing Watersheds

Stream corridor erosion can majorly contribute to the overall sediment and phosphorus load in urbanizing watersheds. However, the relative contribution of stream bed and bank erosion, compared with upland watershed sources and the potential for stream restoration to mitigate total contaminant loads, is poorly understood. In this study, a new method was developed, using the percent impervious cover (PIC) indicator of urbanization to evaluate the relative contribution of the stream corridor versus upland watershed contributions to observed total sediment and phosphorus loads in the receiving watercourse. This method was used to develop a cost-optimized mitigation plan, including implementing low-impact development (LID) stormwater infrastructure for urban areas and agricultural best management practices (BMPs) for rural areas in the watershed and stream restoration for the degraded stream reaches. A new cost–benefit analysis methodology is developed and used to assess the relative benefits of the mitigation measures for the case study of the Tannery Creek sub-watershed of the East Holland River in Ontario, Canada. The novel contributions of this study include the development of three relationships to estimate sediment and associated phosphorus loading based on contributing catchment area and land use, as well as a method to optimize the costs and benefits of planned mitigation measures. The results support stream restoration as an essential and cost-effective part of a comprehensive water quality watershed management plan to help maintain healthy streams in urbanized watersheds.

A new analytical stormwater model for bioretention systems considering both infiltration and saturation excess runoff generation processes

Bioretention systems are increasingly used as a typical stormwater management measure due to their flexibility of scale and general aesthetic appeal. The main purpose of bioretention systems is to control runoff and their runoff reduction efficiency is affected by parameters such as contributing catchment area, fillings and sizes. Conventional analytical probabilistic studies on bioretention systems only considered saturation excess runoff for simplicity and may cause inaccuracy of estimating runoff. In this study, an analytical stochastic model (ASM) for bioretention systems considering both infiltration-excess and saturation-excess runoff generation processes was derived. The proposed ASM model was validated in a large number of case studies in Guangzhou, Jinan, and Lanzhou, China. Various climate, soil, dimension and land use conditions were investigated and compared. Close agreement was observed between the results obtained from the ASM model and continuous simulation results. The ASM model can be used to conveniently evaluate the runoff reduction efficiency of bioretention systems under different configurations of design parameters. It thus provides a computationally efficient analytical tool for the rapid design, analysis and evaluation of the nature-based solution to sustainable urban stormwater management.

Disproportionate and chronic sediment delivery from a fluvially controlled, deep‐seated landslide in Aotearoa New Zealand

AbstractPast research has highlighted the importance of sediment delivery from multiple‐occurrence regional landslide events triggered by storms or earthquakes. Herein, we examine delivery from a more persistent source of sediment, that of a large, slow‐moving landslide in the soft‐rock hill country of Aotearoa New Zealand. We map and monitor the 80‐ha Rangitikei Landslide from 2015 to 2019 using time‐lapse photography, ground surveys, photogrammetry, and piezometers. We show that the landslide can be divided into several zones with distinctive movement patterns, but all zones respond to river erosion. The fastest zone moves more than 10 m per year in a flow‐like fashion, while other zones move 0.01 m per year via slow sliding. Movement occurs all year round, but is two to three times faster in winter and spring. While rainfall and associated groundwater change are commonly attributed to landslide movement patterns, our data show that river flow correlates closely with the weekly to seasonal variability in movement of the landslide toe. This suggests that fluvial erosion can play an important role in the movement dynamics of highly coupled landslides. We estimate an annual sediment yield to the Rangitikei River of at least 40 000 tonnes, in this first quantification of sediment delivery from an active soft‐rock landslide in Aotearoa. This volume implies 7% of the total catchment suspended sediment yield is derived from 0.03% of the contributing catchment area, demonstrating the disproportionate effect of this (and likely other) deep‐seated landslide(s) as a source of sediment in the Rangitikei catchment. Sediment delivery is more continuous than the episodic supply of multiple‐occurrence regional landslide triggering events, and by delivering mostly fine‐grained sediment, it has a potentially large impact on water quality.

Semi-automating the calculation of catchment scale geomorphic controls on river diversity using publically available datasets

The global availability of Digital Elevation Models (DEMs) has enabled rapid, catchment scale geomorphic analysis of river systems. In this paper, we present a semi-automated GIS approach to quickly and accurately extract catchment scale geomorphic controls: slope, gross stream power and valley bottom width, and import bed material texture data along a drainage network. To enable rapid applicability of this approach, we provide the workflow for calculating elevation, slope, contributing catchment area and gross stream power embedded within ArcGIS toolkit, ArcGIS ModelBuilder and Python script as supplementary data. We also present an approach for disaggregating the drainage network and deciding the most appropriate reach length over which to calculate slope based on catchment topography. We demonstrate the importance of investigating DEM quality prior to use, strategic selection of the flow accumulation algorithm, and validation of the drainage network output using aerial imagery.

Flood trends in Europe: are changes in small and big floods different?

Abstract. Recent studies have revealed evidence of trends in the median or mean flood discharge in Europe over the last 5 decades, with clear and coherent regional patterns. The aim of this study is to assess whether trends in flood discharges also occurred for larger return periods, accounting for the effect of catchment scale. We analyse 2370 flood discharge records, selected from a newly available pan-European flood database, with record length of at least 40 years over the period 1960–2010 and with contributing catchment area ranging from 5 to 100 000 km2. To estimate regional flood trends, we use a non-stationary regional flood frequency approach consisting of a regional Gumbel distribution, whose median and growth factor can vary in time with different strengths for different catchment sizes. A Bayesian Markov chain Monte Carlo (MCMC) approach is used for parameter estimation. We quantify regional trends (and the related sample uncertainties), for floods of selected return periods and for selected catchment areas, across Europe and for three regions where coherent flood trends have been identified in previous studies. Results show that in northwestern Europe the trends in flood magnitude are generally positive. In small catchments (up to 100 km2), the 100-year flood increases more than the median flood, while the opposite is observed in medium and large catchments, where even some negative trends appear, especially in northwestern France. In southern Europe flood trends are generally negative. The 100-year flood decreases less than the median flood, and, in the small catchments, the median flood decreases less compared to the large catchments. In eastern Europe the regional trends are negative and do not depend on the return period, but catchment area plays a substantial role: the larger the catchment, the more negative the trend.

Design flood estimation and utility of high‐resolution calibration data in small, heavily urbanised catchments

Design flood estimates are often required for small, heavily urbanised catchments, which respond quickly to storm events. However, hydrological models are most frequently calibrated using daily or hourly data on larger, more rural catchments, which respond on much longer timescales. Here, we calibrate a lumped, conceptual rainfall‐runoff model (ReFH2) in three small (2–6 km2), heavily urbanised catchments in Swindon, UK, assessing the benefits of using high‐resolution temporal and spatial data. Modelling shows that heavy urbanisation does not by itself invalidate the applicability of a lumped, conceptual model. However, we find great dissimilarities between runoff behaviour in different heavily urbanised catchments, with some types behaving similarly to rural catchments. In other cases, response and contributing catchment area can depend more on underground topology than catchment topography. Calibrated runoff response is insensitive to the temporal resolution of the calibration events in all study catchments. Future research should aim to differentiate between different types of heavily urbanised catchment, potentially through landscape metrics to measure the connectivity and isolation of different land surface types.

AN EQUITABLE APPROACH FOR COMPENSATING MUNICIPALITIES OF THE RIO GRANDE WATERSHED FOR ELECTRICITY GENERATED BY THE FURNAS HYDROPOWER PLANT, BRAZIL

Abstract. In Brazil, ninety percent of total electric power comes from renewable sources, where hydropower represents 2/3 of the national energy matrix. In 2012, the new Federal Forest Code eliminated environmental protection along drainage divides and reduced the mandatory width of riparian zones, allowing for land cover change in these environmentally sensitive areas. The conversion of forestlands to agriculture will subject hydroelectric reservoirs to a growing load of sediments, shortening their useful life. In this study of the Furnas hydropower plant and its contributing basin, in the upper reaches of the Rio Grande, a re-evaluation of factors that determine the distribution of finances accrued from hydroelectric generation is recommended. Under the current policy, royalties are paid by the Furnas facility to states and municipalities in direct relation to the area of land flooded by its reservoir, whereas contributing rainfall precipitating in municipalities upstream of the lake is not considered. Currently, the 31 municipalities with lands flooded by the reservoir receive an average of R$ 213,107 (US$ 67,226) annually, while the remaining 172 municipalities in the basin receive no water royalties. In the proposed approach to redistribute these funds, each of the 203 municipalities will receive compensation determined by their contributing catchment area, averaging R$32,543 (US$ 10,266) per year. By considering distribution of rainfall in order to equitably allocate hydroelectric royalties, a system for the payment of environmental services is conceived. Such a system intends to incent stakeholders to protect or replant native forests along drainage divides and riparian zones, in recognition of the value this vegetation has in the reduction of long term costs for hydroelectric facilities.

A landscape-scale approach to examining the fate of atmospherically derived industrial metals in the surficial environment

Industrial metals are now ubiquitous within the atmosphere and their deposition represents a potential source of contamination to surficial environments. Few studies, however, have examined the environmental fate of atmospheric industrial metals within different surface environments. In this study, patterns of accumulation of atmospherically transported industrial metals were investigated within the surface environments of the Snowy Mountains, Australia. Metals, including Pb, Sb, Cr and Mo, were enriched in aerosols collected in the Snowy Mountains by 3.5–50 times pre-industrial concentrations. In sedimentary environments (soils, lakes and reservoirs) metals showed varying degrees of enrichment. Differences were attributed to the relative degree of atmospheric input, metal sensitivity to enrichment, catchment area and metal behaviour following deposition. In settings where atmospheric deposition dominated (ombrotrophic peat mires in the upper parts of catchments), metal enrichment patterns most closely resembled those in collected aerosols. However, even in these environments significant dilution (by 5–7 times) occurred. The most sensitive industrial metals (those with the lowest natural concentration; Cd, Ag, Sb and Mo) were enriched throughout the studied environments. However, in alpine tarn-lakes no other metals were enriched, due to the dilution of pollutant-metals by catchment derived sediment. In reservoirs, which were located lower within catchments, industrial metals exhibited more complex patterns. Particle reactive metals (e.g. Pb) displayed little enrichment, implying that they were retained up catchment, whereas more soluble metals (e.g., Cu and Zn) showed evidence of concentration. These same metals (Cu and Zn) were depleted in soils, implying that they are preferentially transported through catchments. Enrichment of other metals (e.g. Cd) varied between reservoirs as a function of contributing catchment area. Overall this study showed that the fate of atmospherically derived metals is complex, and depends upon metal behaviour and geomorphic processes operating at landscape scales.

The Impact of Changing Storage Area on Flood Magnitude and Occurrence

This study focuses on the impact of combined catchment and storage upon flood occurrences and flood peaks. A significant factor that plays an important role of the combined catchment and storage is the ratio of contributing catchment area to storage area (AC/AS) where the impact significantly shows increasing frequency of storage overflow and flood peaks with the increasing of AC/AS. Some case studies examined in this work, i.e. Way Pegadungan (Lampung, Sumatra) and NagaraRiver (South Kalimantan) catchments show similar behavior. Swamps located on the sides of downstream of Way Pegadungan as well as Nagara River act as storages during flood events. The dyke which was planned to be built increases the ratio of AC/AS significantly as storage area reduced considerably. This has an impact on flood peaks which can increase considerably. The improved understanding of these process controls will be useful in assisting the management of such catchments, particularly to assist in flood prevention and mitigation.

A review of sediment and nutrient concentration data from Australia for use in catchment water quality models

Land use (and land management) change is seen as the primary factor responsible for changes in sediment and nutrient delivery to water bodies. Understanding how sediment and nutrient (or constituent) concentrations vary with land use is critical to understanding the current and future impact of land use change on aquatic ecosystems. Access to appropriate land-use based water quality data is also important for calculating reliable load estimates using water quality models. This study collated published and unpublished runoff, constituent concentration and load data for Australian catchments. Water quality data for total suspended sediments (TSS), total nitrogen (TN) and total phosphorus (TP) were collated from runoff events with a focus on catchment areas that have a single or majority of the contributing area under one land use. Where possible, information on the dissolved forms of nutrients were also collated. For each data point, information was included on the site location, land use type and condition, contributing catchment area, runoff, laboratory analyses, the number of samples collected over the hydrograph and the mean constituent concentration calculation method.A total of ∼750 entries were recorded from 514 different geographical sites covering 13 different land uses. We found that the nutrient concentrations collected using “grab” sampling (without a well defined hydrograph) were lower than for sites with gauged auto-samplers although this data set was small and no statistical analysis could be undertaken. There was no statistically significant difference (p<0.05) between data collected at plot and catchment scales for the same land use. This is most likely due to differences in land condition over-shadowing the effects of spatial scale. There was, however, a significant difference in the concentration value for constituent samples collected from sites where >90% of the catchment was represented by a single land use, compared to sites with <90% of the upstream area represented by a single land use. This highlights the need for more single land use water quality data, preferably over a range of spatial scales. Overall, the land uses with the highest median TSS concentrations were mining (∼50,000mg/l), horticulture (∼3000mg/l), dryland cropping (∼2000mg/l), cotton (∼600mg/l) and grazing on native pastures (∼300mg/l). The highest median TN concentrations are from horticulture (∼32,000μg/l), cotton (∼6500μg/l), bananas (∼2700μg/l), grazing on modified pastures (∼2200μg/l) and sugar (∼1700μg/l). For TP it is forestry (∼5800μg/l), horticulture (∼1500μg/l), bananas (∼1400μg/l), dryland cropping (∼900mg/l) and grazing on modified pastures (∼400μg/l). For the dissolved nutrient fractions, the sugarcane land use had the highest concentrations of dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP). Urban land use had the highest concentrations of dissolved inorganic phosphorus (DIP). This study provides modellers and catchment managers with an increased understanding of the processes involved in estimating constituent concentrations, the data available for use in modelling projects, and the conditions under which they should be applied. Areas requiring more data are also discussed.

Flow pattern and hydraulic performance of the REDAC Gross Pollutant Trap

This paper discusses the flow pattern and hydraulic performance of a Gross Pollutant Trap (GPT), designed and patented by River Engineering and Drainage Research Centre (REDAC) at Universiti Sains Malaysia. Stormwater problems have become more severe due to the increase in urbanization. The increase in the amount of impervious surface in urban areas produces more stormwater runoff, that is carried to the receiving bodies of water. The higher runoff volume also carries more pollutants (gross pollutants, sediments, and nutrients) from the contributing catchment area. Coarse sediments transported by stormwater runoff have negative effects on the receiving body of water and the aquatic environment by covering up aquatic habitats and clogging waterways. One of the challenges in designing a GPT for urban stormwater drainage is providing effective trapping without hindering the hydraulic function of the channel, thus, avoiding overspill or flooding. The current study presents a GPT design to meet these specific requirements of trapping efficiency and hydraulic function. The current GPT overcame the common problem of overspilling of gross pollutants in GPT by the introduction of additional overspill compartments that can handle excessive runoff and improve pollutant trapping in higher flow conditions. In laboratory testing, the prototype GPT was capable of achieving good trapping efficiency (over 80% for gross pollutants and over 60% for coarse sediments) without causing any overspill.

Evaluation of catchment contributing areas and storm runoff in flat terrain subject to urbanisation

Abstract. Contributing Catchment Area Analysis (CCAA) is a spatial analysis technique developed and used for estimation of the hydrological connectivity of relatively flat catchments. It allows accounting for the effect of relief depressions on the catchment rainfall-runoff relationship which is not commonly considered in hydrological modelling. Analysis of distributed runoff was based on USDA runoff curves numbers (USDA, 1986), which utilised the spatial information on land cover and soil types, while CCAA was further developed to define catchment area contributing to river discharge under individual rainfall events. The method was applied to the Southern River catchment, Western Australia, showing that contributing catchment area varied from less than 20% to more than 60% of total catchment area under different rainfall and soil moisture conditions. Such variability was attributed to a compensating effect of relief depressions. CCAA was further applied to analyse the impact of urbanisation on the catchment rainfall-runoff relationship. It was demonstrated that in addition to an increase in runoff coefficient, urbanisation leads to expansion in the catchment area contributing to the river flow. This effect was more evident for the most frequent rainfall events, when an increase in contributing area was responsible for a 30–100% rise in predicted catchment runoff.

Investigating Channel Response to a Dambreak Flood Event in an Alpine River—Downstream Trends in Stream Power and Channel Bed Particle Characteristics

Fieldwork within the framework of SEDAG (SEDiment cascades in Alpine Geosystems) has focused on hydrology, fluvial sediment transport dynamics, and hydrogeomorphological characteristics of the alpine river Partnach (Reintal Valley, Bavarian Alps, Germany). In August 2005 a dambreak flood occurred in the Reintal Valley. The contributing catchment area supplying material for bed load transport at the outlet of the catchment has been enlarged by more than 33% (4.3 km2 + 1.6 km2) due to lake infilling, and thus, reconnecting formerly disconnected parts of the catchment. Post-dambreak downstream variation of total and specific stream power, bed shear stress, and particle characteristics (size and shape) were determined and compared with pre-dambreak findings. As to our knowledge, results of pre- and post-dambreak fluvial-geomorphic investigations have not been published so far for an individual river. Results show high values for total and specific stream power in the post-dambreak regime. In addition, general trends for downstream decreasing in particle size, stream power, and bed shear stress show a degree of regularity after disturbance. Nevertheless, further adjustments of the Partnach channel system in response to the dambreak event are expected in the near future.

Investigating Channel Response to a Dambreak Flood Event in an Alpine River—Downstream Trends in Stream Power and Channel Bed Particle Characteristics

Fieldwork within the framework of SEDAG (SEDiment cascades in Alpine Geosystems) has focused on hydrology, fluvial sediment transport dynamics, and hydrogeomorphological characteristics of the alpine river Partnach (Reintal Valley, Bavarian Alps, Germany). In August 2005 a dambreak flood occurred in the Reintal Valley. The contributing catchment area supplying material for bed load transport at the outlet of the catchment has been enlarged by more than 33% (4.3 km2 + 1.6 km2) due to lake infilling, and thus, reconnecting formerly disconnected parts of the catchment. Post-dambreak downstream variation of total and specific stream power, bed shear stress, and particle characteristics (size and shape) were determined and compared with pre-dambreak findings. As to our knowledge, results of pre- and post-dambreak fluvial-geomorphic investigations have not been published so far for an individual river. Results show high values for total and specific stream power in the post-dambreak regime. In addition, general trends for downstream decreasing in particle size, stream power, and bed shear stress show a degree of regularity after disturbance. Nevertheless, further adjustments of the Partnach channel system in response to the dambreak event are expected in the near future.

Constraining landscape development of the Sri Lankan escarpment with cosmogenic nuclides in river sediment

Escarpments are prominent morphological features along high-elevation passive margins. Recent studies integrating geomorphology, thermochronology, and cosmogenic nuclide-based denudation rate estimates suggest a rapid phase of denudation immediately after the earliest stages of seafloor spreading, and subsequent slow denudation rates since. To constrain the geomorphic evolution of passive margins, we have examined the development of the Sri Lankan escarpment. Cosmogenic nuclide data on river sediment along a north–south transect across the southern escarpment reveal that the landscape is eroding ten times more rapidly in the escarpment zone (26 to 71 mm kyr − 1 ) than in the high-elevation plateau above it and in the lowland plain beneath it (2.6 to 6.2 mm kyr − 1 ). Unlike these low denudation rate areas, the escarpment denudation is strongly and linearly hill slope-dependent. This shows that denudation and retreat are tightly interlinked within the escarpment, which suggests that the escarpment is evolving by rift-parallel retreat, rather than by escarpment downwearing. Supporting evidence is provided by the morphology of rivers draining the escarpment zone. These have steep bedrock channels which show sharp and prominent knickpoints along their longitudinal profiles. It appears that fluvial processes are driving escarpment retreat, as rivers migrate headwards were they incise into the high-elevation plateau. However, the average catchment-wide denudation rates of the escarpment zone are low compared to the denudation rates that are estimated for constant escarpment retreat since rifting. In common with other escarpments worldwide, causes for this slow down can be tectonic change related to flexural bending of the lithosphere, climate change that would vary the degree of precipitation focused into the escarpment, or the decrease in the contributing catchment area, which would reduce the stream power available for fluvial erosion.

Geomorphometric characteristics of New Zealand landslide dams

This study presents results from a quantitative analysis of a new inventory of n=232 landslide dam occurrences in New Zealand. Previously published data were expanded by documentation of recent events and evidence from a regional air-photo reconnaissance focused on the upland regions of southwestern South Island. Additional geomorphometric data on landslide dams, associated lakes, and contributing catchment characteristics, were extracted from a 25-m Digital Elevation Model (DEM), augmented by limited ground truthing, and compiled in a GIS-based inventory. The New Zealand case examples fall into the global trend, although they contain both two extremely large features in terms of landslide dam volume V D and lake volume V L. Analysis suggests that landslide dam height H D, landslide dam volume V D, lake volume V L, contributing catchment area A C, and local relief H R, are key variables for assessing landslide dam stability independently from other catchment parameters such as lithology, climate, or dam sedimentology. They may be provisionally used as representative characteristics of landslide dams, irrespective of environmental boundary conditions, such as climate, geology, or site-specific valley geomorphometry. Three newly proposed dimensionless indices, i.e., the Backstow Index I s, Basin Index I a, and Relief Index I r, based on landslide dam height H D allow limited, yet promising, preliminary assessments of landslide dam stability. Compared with worldwide examples, they also demonstrate a much narrower conditional range for the formation of stable landslide dams in New Zealand. Catchment parameters such as maximum elevation E max, upstream relief H R, contributing catchment area A C, and relief ratio R R are significantly different at sites of former and existing landslide-dammed lakes, and may be used as independent variables in future terrain-based classification schemes. Generally, data are incomplete with underreporting of small and ephemeral landslide dams, and over-representation of earthquake case studies. Nonparametric correlation highlights the statistical interdependence between geomorphometric variables as an artefact of initial data calculation, while varying accuracy poses a significant drawback for complex multivariate statistical techniques such as principal component, cluster, or discriminant analyses.

The Loch Dee Project: runoff and surface water quality in an area subject to acid precipitation and afforestation in SW Scotland

ABSTRACTA description is given of the hydrological regime and associated surface water quality recorded at a multi-disciplinary long-term investigation into the effects of acid precipitation and afforestation. The study catchment at Loch Dee is situated on the margins of the Loch Doon granite complex in SW Scotland. Annual rainfall is in excess of 2200 mm. The three main tributary burns exhibit a rapid response to rainfall with a high percentage of direct runoff. The loch with an average volume of 3650 M1 and a contributing catchment area of 15·6 km2 has an average turn-over of approximately forty days but this has varied from 15 to 100 days. Local physical variations are shown to influence both hydrological response and surface water quality. Generally stream water during spate conditions reflects rainfall chemistry. Occasionally, however, moderately acid rainfall containing large concentrations of sea salts has produced highly acidic runoff through a process of ion-exchange within the surface horizons of the soils. The quality of base flows shows a spatial variation which reflects various lithologies to the extent that pH values ranging from 4·9 to 6·9 have been observed.