Vegetation Encroachment Research Articles

Vegetation patterns along agricultural land abandonment in the Balkans

AbstractQuestionWhat are the woody vegetation encroachment patterns after agricultural land abandonment? Focusing on two parameters, woody plant species richness and vertical vegetation heterogeneity (number of different vegetation strata and their relative cover) we investigated: (a) the effect of forest encroachment following land abandonment; (b) the comparative importance of forest encroachment vis‐a‐vis topographic and climatic parameters, and finally; (c) the ecological importance of eight land‐cover types encountered in abandoned agricultural landscapes.LocationThe Balkan Peninsula (Albania, Bulgaria, Croatia, Greece).MethodsWe set up a standard methodology for 1 × 1 km site selection (70 sites) and data collection within 497 plots, along a well‐defined forest encroachment gradient that reflects land abandonment in terms of woody vegetation cover.ResultsThe pattern that emerged was neither clear nor common for the Balkan region, regarding the effect of forest encroachment on the woody plant species richness in young forests, formed from 20 to 50 years after land abandonment. However, at national level, species diversity was significantly affected by elevation (Bulgaria and Croatia) and temperature (Croatia), with lower and cooler areas being richer. Elevation was of great importance in determining vertical vegetation heterogeneity. Woodlots, broad‐leaved forests, hedges and shrublands held the highest woody species richness in comparison to the more open land‐cover types, and vertical vegetation heterogeneity was higher in open forests and woodlots.ConclusionsWe expect the expansion of broad‐leaved forests following land abandonment to enhance woody species richness. However, other land‐cover types that were found to be important for woody plants should be maintained. As woody plants play a key role in supporting overall biodiversity, by providing suitable habitat for many species, we consider the preservation of a mosaic of patches of different land‐cover types essential for the conservation of both plant and animal species diversity. Young forests should be preserved at intermediate stages of succession, through intermediate disturbance activities, including medium intensity grazing and the enhancement of wild ungulates.

Long‐term sand dune spatio‐temporal dynamics and endemic plant habitat extent in the Athabasca sand dunes of northern Saskatchewan

AbstractThe Athabasca sand dunes in northern Saskatchewan and north‐east Alberta are a unique landscape of moving sand that hosts nine narrowly distributed endemic vascular plant taxa. We modeled the extent of habitat for each species, corresponding dune morphologies in species habitat, spatial and temporal variation in dune environments, and rates of woody vegetation encroachment at dune boundaries to support an assessment of long‐term threats for the Athabasca endemic dune flora. Landsat images were used to maximize the time spans and areal coverage of the study. The Athabasca sand dunes are currently active and characterized morphologically by crescentic ridge and morphodynamically by transverse form dunes. Longitudinal sand movement parallel to the dune axis resulted in the creation of new dune areas along the east and south‐east boundaries of the dune fields at a rate of 0.14 km2 year−1. Forest succession along the western boundaries of the dune fields resulted at an annual dune loss of 1.98 km2 year−1. The net extent of dune stabilization between 1985 and 2014 was 53.76 km2 or nearly 20 percent of the total open sand dune extent. All habitat modeling methods showed robust performance (>0.5 AUC), with the best performance in most cases from generalized linear models. Estimated total available/occupied habitat was comparatively low for the least abundant species Achillea millefolium (38.92 km2) and Armeria maritima (48.82 km2), and of those areas 53.5% and 16.29%, respectively, are influenced by dune stabilization. Continuing stabilization of the Athabasca sand dunes region may present conservation concerns for these narrowly distributed endemic taxa.

Savanna turning into forest: concerted vegetation change at the ecotone between the Amazon and “Cerrado” biomes

In the “Cerrado”–Amazon ecotone in central Brazil, recent studies suggest some encroachment of forest into savanna, but how, where, and why this might be occurring is unclear. To better understand this phenomenon, we assessed changes in the structure and dynamics of tree species in three vegetation types at the “Cerrado”–Amazon ecotone that are potentially susceptible to encroachment: open “cerrado” (OC), typical “cerrado” (TC) and dense woodland (DW). We estimated changes in density, basal area and aboveground biomass of trees with diameter ≥ 10 cm over four inventories carried out between 2008 and 2015 and classified the species according to their preferred habitat (savanna, generalist, or forest). There was an increase in all structural parameters assessed in all vegetation types, with recruitment and gains in basal area and biomass greater than mortality and losses. Thus, there were net gains between the first and final inventories in density (OC: 3.4–22.9%; TC: 1.8–12.6%; DW: 0.2–8.3%), in basal area (OC: 8.3–18.2%; TC: 2–12.7%; DW: 2.3–8.9%), and in biomass (OC: 10.6–16.4%; TC: 1–12%; DW: 5.2–18.7%). Furthermore, all vegetation types also experienced net gains in forest and generalist species relative to savanna species. A decline in recruitment of savanna species was a likely consequence of vegetation encroachment and environmental changes. Our results indicate, for the first time based on quantitative and standardized multi-site temporal data, that concerted structural changes caused by vegetation encroachment are occurring at the ecotone between the two largest biomes in Brazil.

Evolution of river planforms downstream of dams: Effect of dam construction or earlier human‐induced changes?

AbstractWhen studying the evolution of landscape, it is difficult to discriminate the influence of anthropogenic from natural causes, or recognise changes caused by different sources of human action. This is especially challenging when the influence of certain sources is overprinted. For instance, although dam closure is the most common method of altering river courses, dam construction is often preceded by hydro‐technical works such as channel straightening, embankment construction or sediment mining. Both dam construction and the hydro‐technical works that precede dam closure can result in changes in the balance between sediment supply and transport capacity, and often, changes in river planform.The main objective of this study was to verify whether the works preceding dam closure are an important driver of river planform changes on the lower Drava River (Hungary). The case study is based on geological and geophysical surveys, as well as the analysis of historical maps covering an anabranching, 23 km long valley section. We show that channel straightening conducted prior to dam closure resulted in a transition from a meandering to sinuous planform with channel bars. Dam construction itself then caused enhanced incision, exposure of bar surfaces, vegetation encroachment and the formation of an anabranching planform. Based on this study, we developed models of alluvial island and channel planform evolution downstream of dams. Dam construction enhances channel incision, narrowing, and the reduction of flow caused by earlier hydro‐technical works. Many rivers downstream of dams experience episodes of anabranching or wandering, with a multi‐thread pattern replacing sinuous, braided and meandering courses. When incision continues, river patterns evolve from anabranching to sinuous via the attachment of alluvial islands to floodplains. However, the timing and sequence of these changes depend on hydrological and sediment supply regimes, geomorphic settings and anthropogenic actions accompanying dam construction. Copyright © 2018 John Wiley & Sons, Ltd.

Eastern massasauga demography and extinction risk under prescribed‐fire scenarios

ABSTRACTThe use of poorly estimated or surrogate population parameter estimates to assess population viability may result in misleading predictions. Consequently, a critical first step to understanding population health and the effects of land management practices on threatened species is estimation of site‐specific demographic parameters. A major threat to the eastern massasauga (Sistrurus catenatus) is habitat loss due to encroachment of woody vegetation and invasive species. Current land management practices require periodic burning or mowing to maintain habitat suitability. Although these methods improve habitat quality, they may also increase the risk of depredation due to reduced ground cover if burns are too extensive or cause mortality if conducted when snakes are active. We fitted contemporary capture–recapture and matrix models to an 8‐year dataset to estimate population parameters for an eastern massasauga population near the range center of the species, where the largest number of eastern massasauga populations may still persist. From 2009 to 2016, we captured 826 eastern massasaugas 1,776 times. In general, annual survival increased with increasing age (age 0 = 0.38, age 1 = 0.65, age 2 = 0.67, age ≥3 females = 0.71, age ≥3 males = 0.66). Abundance estimates ranged from 84 to 140 adults and annual reproductive frequency was 0.44 (95% CI = 0.29–0.59). We simulated increased mortality due to prescribed burns during spring, fall, and late fall for 50 and 100 years. The baseline model, which incorporated current prescribed‐fire practices, indicated a stable population with only a 0.2–0.6% probability of extinction over 100 years, suggesting that management practices at this site are sustainable if they remain unchanged. Simulations of conservative increases in mortality due to fire changed the probability of extinction little over 50 years (≤0.7%) but increased probability of extinction up to 24.5% over 100 years in the most pessimistic prescribed‐burn scenario. These prescribed‐burn simulations may be comparable to burn regimes used at other eastern massasauga sites. The population parameters estimated here provide information needed for assessing range‐wide population viability and investigating geographic variation in eastern massasauga demography. © 2018 The Wildlife Society.

Biomorphodynamics of alternate bars in a channelized, regulated river: An integrated historical and modelling analysis

AbstractThe development of alternate bars in channelized rivers can be explained theoretically as an instability of the riverbed when the active channel width to depth ratio exceeds a threshold. However, the development of a vegetation cover on the alternate bars of some channelized rivers and its interactions with bar morphology have not been investigated in detail.Our study focused on the co‐evolution of alternate bars and vegetation along a 33 km reach of the Isère River, France. We analysed historical information to investigate the development of alternate bars and their colonization by vegetation within a straightened, embanked river subject to flow regulation, sediment mining, and vegetation management. Over an 80 year period, bar density decreased, bar length increased, and bar mobility slowed. Vegetation encroachment across bar surfaces accompanied these temporal changes and, once established, vegetation cover persisted, shifting the overall system from an unvegetated to a vegetated dynamic equilibrium state.The unvegetated morphodynamics of the impressively regular sequence of alternate bars that developed in the Isère following channelization is consistent with previous theoretical morphodynamic work. However, the apparent triggering dynamics of vegetation colonization needs to be investigated, based on complex biophysical instability processes. If instability related to vegetation colonization is confirmed, further work needs to focus on the relevance of initial conditions for this instability, and on related feedback effects such as how the morphodynamics of bare‐sediment alternate bars may have affected vegetation development and, in turn, how vegetation has created a new dynamic equilibrium state. Copyright © 2018 John Wiley & Sons, Ltd.

Quantifying and predicting the benefits of environmental flows: Combining large‐scale monitoring data and expert knowledge within hierarchical Bayesian models

Abstract Despite large investments of public funds into environmental flows programs, we have little ability to make quantitative predictions of the ecological benefits of restored flow regimes. Rather, ecological predictions in environmental flow assessments typically have been qualitative and based largely upon expert opinion. Widely applicable, quantitative models would help to justify existing flow programs and to inform future planning. Here, we used a hierarchical Bayesian analysis of monitoring data coupled with expert‐derived prior distributions, to develop such a model. We quantified the relationship between the duration and frequency of inundation, and encroachment of terrestrial vegetation into regulated river channels. The analysis was informed by data from 27 sites on seven rivers. We found that longer inundation durations reduce terrestrial vegetation encroachment. For example, a 50‐day continuous inundation during winter reduced predicted vegetation cover to a median of 11% (95% CI: 7%–35%) of cover predicted under non‐inundated conditions. This effect varied among sites and rivers, and was moderated by the frequency of inundation events. The hierarchical structure improved precision of model predictions relative to simpler analysis structures. Informative prior distributions also improved precision relative to minimally informative priors. The hierarchical Bayesian analysis allows us to make quantitative predictions of ecological response under the full range of flow conditions, allowing us to assess the benefits of planned or delivered environmental flows. It can be used to make estimates of ecological effects at sites that have not been sampled, and also to scale up site‐level results to catchment and regional scales. Quantitative predictions of ecological effects provide a more objective risk‐based approach, allowing improved planning of environmental flows and building public confidence in these major investments of public funds.

Ecohydrologic Connections in Semiarid Watershed Systems of Central Oregon USA

An improved understanding of ecohydrologic connections is critical for improving land management decisions in water-scarce regions of the western United States. For this study, conducted in a semiarid (358 mm) rangeland location in central Oregon, we evaluated precipitation-interception-soil moisture dynamics at the plot scale and characterized surface water and groundwater relations across the landscape including areas with and without western juniper (Juniperus occidentalis). Results from this study show that juniper woodlands intercepted up to 46% of total precipitation, altering soil moisture distribution under the canopy and in the interspace. Results indicate that precipitation reaching the ground can rapidly percolate through the soil profile and into the shallow aquifer, and that strong hydrologic connections between surface and groundwater components exist during winter precipitation and snowmelt runoff seasons. Greater streamflow and springflow rates were observed in the treated watershed when compared to the untreated. Streamflow rates up to 1020 L min−1 and springflow rates peaking 190 L min−1 were observed in the watershed where juniper was removed 13 years ago. In the untreated watershed, streamflow rates peaked at 687 L min−1 and springflow rates peaked at 110 L min−1. Results contribute to improved natural resource management through a better understanding of the biophysical connections occurring in rangeland ecosystems and the role that woody vegetation encroachment may have on altering the hydrology of the site.

Influence of flood regime on riparian vegetation dynamics in rivers with alternate bars

Throughout the 20th century, many rivers worldwide have undergone important riparian vegetation encroachment, which can be problematic in terms of flood risks and biodiversity. Nowadays, controlled floods is often considered as a management option in anthropized rivers, with the aim of limiting vegetation encroachment within river channels, as well as maintaining a diverse habitat by reactivating natural channel dynamics. In this context, this study aims at investigating the influence of different flood regimes on river bar vegetation development and dynamics, focussing on alternate bar systems which are typically found in embanked streams. This question has been addressed through two-dimensional bio-morphodynamic modeling of a simplified gravel bed river reach. Four hydrological scenarios with different flood peak discharges have been run for 50 years. For all scenarios, a steady increase in vegetation cover strongly impacts the evolution of bar morphology, until a relatively stable equilibrium is reached after one to three decades. Numerical results suggest that vegetation development on bars is associated to an increase in bar wavelength and a decrease in bar width. Higher peak flood discharges lead to narrower and longer bars, and a longer adjustment duration. When vegetation cover is fully developed, interannual flood variability seems crucial to maintain bedform and vegetation turnover.

Limiting the development of riparian vegetation in the Isère River: A physical modelling study

Physical modelling experiments are conducted to investigate if a modification of the Isère River (French Alps) hydrology by changing dams management is able to foster riverbed morphodynamic and, thus limiting riparian plant development. The experimental setup is a 1:35 scale, undistorted movable bed designed to ensure the Froude number similarity and initial conditions for sediment particle motion. The physical model is 35 m long, 2.6 m wide, with a sand mixture composed of three grain size classes. Two runs with different flow and bed load conditions are simulated. Preliminary results show an intense riverbed activity when the system reaches a dynamic equilibrium state. Under these conditions, bar mobility is strong enough to limit vegetation encroachment only when water discharges are higher than the discharge of a 5-years flood during more than 10 days. These results indicate that the hydrological characteristics of the Isère River and the actual configuration of the hydropower structures could be not able to release annually the flow conditions needed to control riparian plant development.

Recent geomorphological evolution of a natural river channel in a Mediterranean Chilean basin

In this paper we analyse the recent geomorphological evolution of the River Ñuble, an unmodified wandering river in the Mediterranean region of Chile, highlighting the relation between the observed hydroclimatic trends in the region and the morphology of the river. The work documents the recent changes (2003–2016) in channel morphology (i.e., narrowing, simplification, vegetation encroachment) and, in particular, how the river has progressively reduced its geomorphic activity during the last decade. Changes have been detected using aerial imagery and quantified by means of a series of channel form indices that allow tracking the geomorphological evolution of an 8-km river segment. The catchment has experienced a clear decrease in the frequency and magnitude of flood events, although this fact is not fully supported by a generalized reduction in the analysed rainfall series. We relate the observed river relaxation and the associated channel changes with the reported period of low hydroclimatic activity, which follows a humid period that occurred in the Pacific region during the 1970s and 1980s, connected to the PDO (Pacific Decadal Oscillations) that particularly affected the northern and the central parts of Chile. Altogether, this resulted in generalized river stability and a simplification of the drainage pattern of the channel. In absence of river training practices and other major changes in the catchment, the reduction of formative discharges appears thus to be the main control of the recent evolution of this gravel-bed river.

Importance of considering riparian vegetation requirements for the long-term efficiency of environmental flows in aquatic microhabitats

Abstract. Environmental flows remain biased toward the traditional biological group of fish species. Consequently, these flows ignore the inter-annual flow variability that rules species with longer lifecycles and therefore disregard the long-term perspective of the riverine ecosystem. We analyzed the importance of considering riparian requirements for the long-term efficiency of environmental flows. For that analysis, we modeled the riparian vegetation development for a decade facing different environmental flows in two case studies. Next, we assessed the corresponding fish habitat availability of three common fish species in each of the resulting riparian landscape scenarios. Modeling results demonstrated that the environmental flows disregarding riparian vegetation requirements promoted riparian degradation, particularly vegetation encroachment. Such circumstance altered the hydraulic characteristics of the river channel where flow depths and velocities underwent local changes of up to 10 cm and 40 cm s−1, respectively. Accordingly, after a decade of this flow regime, the available habitat area for the considered fish species experienced modifications of up to 110 % when compared to the natural habitat. In turn, environmental flows regarding riparian vegetation requirements were able to maintain riparian vegetation near natural standards, thereby preserving the hydraulic characteristics of the river channel and sustaining the fish habitat close to the natural condition. As a result, fish habitat availability never changed more than 17 % from the natural habitat.

Extraction of power lines using mobile LiDAR data of roadway environment

Assessing the field conditions of power line corridor is important for electrical power providers. Monitoring and management of power line corridor are essential for electric resource management and power corridor safety. Mobile LiDAR is becoming popular in mapping of power line corridors along the roadway. Power lines extraction using mobile LiDAR point cloud of different roadway settings are presented in this paper. The proposed method works in four steps. Initially the horizontal segment containing power lines in the three-dimensional point cloud are filtered out. Then the two-dimensional point density based refining is used to remove the trees and buildings. Hough transform is used to extract power lines and further the missing portions are reconstructed. Three test sites each from urban, peri-urban and rural roadway environment and having different level of complexities along power line corridor are chosen to test the proposed method comprehensively. Occlusions especially the vegetation encroachment in complex roadway environment and their effects in power line extraction is highlighted in this paper. The partially occluded power lines are successfully extracted. The average correctness and completeness of 98.84% and 90.84%, respectively are achieved in the urban, peri-urban and rural test sites.

Holding the line: three decades of prescribed fires halt but do not reverse woody encroachment in grasslands

Encroachment of woody vegetation represents a significant global threat to biodiversity in grasslands, but practices used to reverse encroachment are rarely evaluated comprehensively. Several factors may drive encroachment, such as land use history, alteration of disturbance regimes, and local environment, but their relative importance is poorly understood. Another complicating factor is that encroachment may proceed via positive feedbacks that result in thresholds, beyond which its reversal is difficult. We ask what impact reintroducing frequent fire has on encroachment relative to the influences of landscape context and historical vegetation. We investigate whether woody cover frequency distributions suggest that feedbacks reinforce encroachment after a threshold of woody cover is surpassed. We analyze aerial photos in glade grasslands in Missouri, USA, to assess encroachment patterns over a 75-year period. Fire was excluded from this landscape for the first 45 years, and then reintroduced at varying frequencies in the last 30 years. Woody vegetation cover increased sevenfold from 1939 to 2014 overall. After the reintroduction of prescribed fire, woody cover stayed approximately constant in burned glades, but continued increasing in unburned glades. Woody cover followed bimodal frequency distributions in burned areas. Fire-tolerant vegetation tended to encroach near historically wooded areas, while fire-sensitive vegetation responded more to fire history. Altered disturbance regimes, in addition to numerous recognized drivers, can cause ecosystem state changes associated with losses to biodiversity. Conducting management early in the encroachment process and restoring grasslands at broad landscape scales may help counteract local feedbacks that promote encroachment.

Cost-benefit analysis of native warm season grasses for transmission line right-of way revegetation

The rapid reestablishment of vegetation in newly constructed electric transmission line rights-of-way (ROWs) is important for the control of soil erosion and compliance with associated regulations. Following establishment, routine maintenance must be performed to suppress the encroachment of woody vegetation in ROWs to provide for continuous and safe operation of electric transmission lines. Although non-native seed mixes conventionally are used for this purpose in North America, modeling ROW revegetation on locally adapted native communities could reduce longer-term management needs and provide ecological, environmental, and social benefits associated with native systems. We conducted a cost-benefit analysis to determine if ROW revegetation with a seed mix comprised primarily of native herbaceous species could be cost-effective relative to revegetation with a conventional seed mix comprised primarily of exotic herbaceous species. Our analysis synthesized data collected from a feasibility study of ROWs planted with a native seed mix and information obtained from the Tennessee Valley Authority regarding ROW revegetation and maintenance costs. Overall, the cost of revegetation with native species was ∼5% more expensive per unit area than the cost of revegetation exotic species. The degree of reduced long-term maintenance costs to make revegetation with native species a worthwhile longer-term investment would be 10–17% using a break-even analysis. Despite the initial greater expense of revegetation with native species, we suggest that associated potential maintenance cost savings and ecological, environmental, and social benefits could favor their use.

Conservation genetics of an endemic and threatened amphibian (Capensibufo rosei): a leap towards establishing a genetic monitoring framework

Given the ever-increasing anthropogenic changes to natural ecosystems, it is imperative that temporal changes in genetic diversity be monitored to help safeguard the future viability of species. Capensibufo rosei is a small, range-restricted bufonid from South Africa, believed to have experienced an enigmatic decline likely due to the suppression of natural fires and the loss of grazing animals from some areas. Without these disturbances, their habitat becomes overgrown, which might affect the characteristics of their breeding pools. Since the 1980s, four breeding sites have been lost, presumably due to loss of breeding habitat through encroachment of vegetation. Currently, there are only two known populations [Cape of Good Hope (CGH) and Silvermine nature reserves] both within Table Mountain National Park. Consequently, this species may be vulnerable to stochastic events and genetic erosion through the loss of metapopulation connectivity. To assess the genetic status of this species, genetic diversity within both populations was quantified for two time periods using 11 microsatellite markers. Despite evidence of severe population bottlenecks, both populations possess levels of diversity similar to other anurans, and Silvermine has greater diversity than CGH. A close examination of the data revealed both populations to be genetically dynamic through time, with the loss and gain of rare alleles. Both populations also experienced a slight increase in overall diversity between sampling periods. While the latter was not statistically significant, the monitoring period was perhaps too short to understand changes in diversity over time. These results will form the baseline for future monitoring to better understand this threatened and declining species and to track genetic erosion or recovery.

What drives riparian vegetation encroachment in braided river channels at patch to reach scales? Insights from annual airborne surveys (Drôme River, SE France, 2005–2011)

AbstractUnderstanding riparian vegetation encroachment and its drivers is crucial for predicting alluvial river channel morphodynamics in different hydro‐climatic contexts. We investigated fine‐scale vegetation encroachment patterns and underlying physical controls along the Drôme River, France, following a 50‐year flood in 2003. Our study addressed the following questions: (a) What is the relative timing and the respective importance of vegetation patch recruitment versus patch expansion? (b) How well do regional/climatic factors explain the spatio‐temporal patterns of recruitment and expansion versus local and reach‐scale variation in geomorphic position and habitat? Along a 3‐km reach, we analysed a chronosequence of high‐resolution aerial images acquired yearly between 2005 and 2011. From each image series, we digitized patches of newly recruited vegetation and their lateral extent in following years to determine their expansion. This was complemented by elevation and plant structure data from airborne LiDAR data and field observations. The initial post‐flood vegetated area doubled within 6 years, with a pronounced recruitment peak in 2006–2007. Patch expansion showed a positive linear relationship to growing season temperature. Vegetation encroachment was greatest in a slightly aggrading sub‐reach compared to an incising sub‐reach. Initially, it occurred principally along low flow channel margins and on bar surfaces, later in intermittent channels. Our results confirmed that extensive recruitment can succeed floods with recurrence intervals smaller than 1‐in‐5 to 10 years, when the flood history resets the geomorphic framework. Recruitment extent depends in part on local hydrological connectivity, whereas higher temperatures can boost plant growth where there is a perennial water supply.

30-year response to damming of a Mediterranean river in California, USA

Dry Creek is a major tributary of the Russian River in Northern California (USA) that has experienced hydrologic and morphologic alterations after the closure of Warm Springs Dam in 1983. Our objective is to present a detailed diagnosis of the modification of the creek’s flow and sediment regimes, and interpret the alterations regarding the ecomorphologic evolution previously observed in the creek. Statistical analysis of the river’s flow and sediment series indicates that dam operation has had significant impacts on the magnitude and frequency of occurrence of the highest floods, and the magnitude, variability, and duration of low and very low flows. Similarly, sediment concentration and discharge have also experienced major alterations. Loss of habitat complexity for native flora and fauna (especially endangered salmonids), channel incision, and vegetation encroachment are some of the negative trends found for the creek over the last 30 years, since river regulation began. We discuss the present dynamics of the river and propose, on that basis, the improvement of its hydromorphic functioning as part of future large-scale restoration initiatives.

An evidence-based approach for integrating ecological, hydrological and consumptive models to optimize flow management: a proof of concept

ABSTRACTImplementing policies to return water to the environment is challenging. We developed an approach to integrate ecological responses with river management models to provide a link between flow and ecology. This paper aims to summarize the findings of a multifaceted project bringing together multiple lines of evidence to achieve a proof-of-concept approach for optimizing water use to support water policy and management decisions. We developed an eco-hydrology model that represents rivers, water storages, operational constraints, flow management, an ecological response and consumptive irrigation demands, which is linked to climate. To demonstrate the proof of concept, we describe a case study where modelling optimization seeks solutions to minimize terrestrial vegetation encroachment (an ecological response) and maximize irrigation net value through flow management. The solutions provide a range of alternative ‘optimal’ management options to consider. Ultimately, hydrological modelling that integrates both consumptive use and ecological response simultaneously is important to enhance stakeholder understanding of the complexities and trade-offs involved in implementing different decisions. Although proof of concept at this stage, the approaches offer potential for integration of river management models and quantitative ecological response models (derived by considering available evidence from many sources) to support water policy and management decisions.

영주댐 운영 전 내성천에서 하도 형태의 단기 변화

내성천은 산지를 사행하는 모래하천으로 오랫동안 그 하천지형학적 특성을 유지해왔다. 그러나 최근 식생의 활착으로 종래의 경관을 상실해 가고 있다. 본 연구에서는 내성천 장기조사 연구의 일환으로 내성천의 56.8 km 구간을 대상으로 지난 2012 - 2016년 기간에 발생한 지형변화를 분석하였다. 항공 라이다 및 하천측량이 시행되었고 수문자료와 현장 조사자료가 함께 활용되었다. 주요 4개 지점중에서 만곡부 지점에서는 만곡사주가 확장되었고, 직선구간에서는 하중 사주가 발달하였다. 한 두 번의 유사 퇴적으로 인해 발생한 하중 사주의 고도 변화는 0.6 - 1.4 m에 달하였으나 하상저하는 분명하지 않았다. 이러한 변화는 2014 - 2015년의 갈수기에 식생이 크게 활착하였다가 2016년에 홍수로 인해 퇴적이 일어난데 기인하는 것으로 보인다. 이러한 과정은 이전에 내성천 중하류 구간에 형성되어 있는 하중도의 주된 형성과정으로 판단된다. The Naeseong Stream is a meandering sand-bed stream flowing through mountains and has so long maintained its geomorphological uniqueness characterized by extensive braided bare bars. Recently, its long-lasting landscape has been changed due to encroachment of vegetation. In this study being a part of long-term monitoring research morphological changes of the 56.8 km long study reach of the Naeseong Stream, which occurred during the period of 2012 - 2016 were analyzed. Airborne LiDAR and terrestrial cross-section surveys were carried out. Hydrological and on-site investigation data were also collected. Among the main four sites, two bend reaches showed point bars enlarged, while along the other two straight reaches mid-channel bars were either newly formed or increased in area and height. At the highest deposition point of each bar, vertical changes which were caused by one or two times of sediment deposition amounted to 0.6 - 1.4 m. On the contrary channel bed degradation was not obvious. Overall morphological changes in the study reach were attributed to deposition of sediment which occurred during the flood in July 2016 on the bar surfaces vegetated during the precedent dry seasons. These kind of geomorphological processes are thought to be the same as those related to the existing mid-channel islands along the mid- and downstream reach of the Naeseong Stream.