Publikasjoner
NIBIOs ansatte publiserer flere hundre vitenskapelige artikler og forskningsrapporter hvert år. Her finner du referanser og lenker til publikasjoner og andre forsknings- og formidlingsaktiviteter. Samlingen oppdateres løpende med både nytt og historisk materiale. For mer informasjon om NIBIOs publikasjoner, besøk NIBIOs bibliotek.
2022
Forfattere
Yvonne RognanSammendrag
English summary On behalf of Tinfos AS, NIBIO and Faun Nature Management carry out environmental monitoring of the river Hovlandsåna during the construction of a new powerplant at Flateland in Vegusdal (Birkenes municipality). The environmental monitoring includes continuous monitoring of water quality, quarterly and weekly sampling, as well as biological surveys at a total of three stations in Hovlandsåna. This quarterly report includes results from preliminary studies (water samples, benthic animals and algae carried out on 21.10.2021), results for weekly water samples in the period 30.11.2021 - 30.03.2022 (4th quarter 2021 and 1st quarter 2022) and measurement data from continuous monitoring at two stations in Hovlandselva from 13.10.2021 - 30.11.2021 (4th quarter 2021). The construction work related to the establishment of the Flateland power plant has so far had low impact on the water quality in Hovlandsåna. With the exception of some elevated turbidity values 25.10. - 07.11.2021, no exceedances of the limit values given by the County Governor of Aust- and Vest-Agder (State Administrator in Agder) have been registered. The elevated turbidity values were registered during the establishment of a connection site to provide electrical power to Nygårdsdalen from the power grid running along the river and Fv42. The overall condition in the Hovland River is «good» and the benthic surveys from HOV_REF, HOV_NED1 and HOV_NED2, showed two species of acidification-sensitive mayflies (ephemeroptera) and several other species were found within families with a high ASPT value. This indicates that the impact of acidification in the river is small and that the liming of the watercourse has given good results. A more even water flow as a result of the changed regulation regime in Vikestølvatnet has also contributed to a significant reduction in leaching of sediments from the beach zone. The anadromous stretch of the river reaches up to Trollfoss and is said to have good populations of sea trout. Good populations of stationary trout (upstream of Trollfoss / Flateland) are also recorded. The anadromous section of the river is likely to be somewhat affected by the construction work for the Flateland power plant and increased focus on this part of the river is required Sammendrag På oppdrag fra Tinfos AS gjennomfører NIBIO og Faun naturforvaltning miljøovervåking av Hovlandsåna under bygging av Flateland kraftverk. Miljøovervåkingen omfatter kontinuerlig overvåking av vannkvalitet, kvartalsvis og ukentlig prøvetaking, samt biologiske undersøkelser ved til sammen tre stasjoner i Hovlandsåna. Denne kvartalsrapporten omfatter resultater fra forundersøkelser (vannprøver, bunndyr og begroing utført 21.10.2021), resultater for ukentlige vannprøver i perioden 30.11.2021 – 30.03.2022 (4. kvartal 2021 og 1. kvartal 2022) og måledata fra kontinuerlig overvåking ved to stasjoner i Hovlandselva fra 13.10.2021 – 30.11.2021 (4. kvartal 2021). Anleggsarbeidene i forbindelse med bygging av Flateland kraftverk har til nå gitt svært liten påvirkning på Hovlandsåna. Med unntak av noen forhøyede turbiditetsverdier i forbindelse med etablering av byggestrøm til Nygårdsdalen 25.10. – 07.11.2021 har det ikke blitt registrert noen overskridelser av grenseverdiene gitt av Fylkesmannen i Aust- og Vest-Agder (Statsforvalteren i Agder).
Forfattere
Yvonne RognanSammendrag
I løpet av 2. og 3. kvartal (Q2 og Q3)2022 har NIBIO og Faun Naturforvaltning gjennomført overvåking av vannkvalitet og biologiske undersøkelser i Hovlandsåna. I løpet av Q2 og Q3 har anleggsarbeidene inkludert etablering av inntaksdam ved Myklebostad, sprengning av overføringstunnel fra Myklebostad til Kjetevatn og tilførselstunnel fra Kjetevatn til Flateland. Sprengningsarbeidene har, som forventet, bidratt til økte konsentrasjoner av nitrogen og perioder med forhøyet pH og turbiditet, særlig ved Flateland og videre nedstrøms. I tillegg har gravearbeidene tilknyttet etablering av inntaksdammen ved Myklebostad bidratt til noe økt turbiditet i elva oppstrøms Trollfoss. Et mindre deponi like nedstrøms Flateland har bidratt til opphopning av sand rundt måleutstyret ved stasjonen HOV NED2. Avrenning fra sidebekker og erosjon fra elvebreddene har vært større i perioder med nedbør. Avrenning av nitrogen i forbindelse med sprengningsarbeidene har ført til at tilstanden for nitrogen har blitt redusert til «moderat» tilstand. Resultatene fra el-fiskeundersøkelsene i september viser at tettheten av ørret ved Flateland tilsvarer en «svært god» tilstand, noe som tilsier at de økte konsentrasjonene av turbiditet og nitrogen ikke har hatt noen tydelig påvirkning på ørret i denne delen av elva.
Forfattere
Trygve S. Aamlid Birgitte Henriksen John Ingar Øverland Jon Sæland Trond Gunnarstorp Erik Aaberg Harald Solberg Geir Kjølberg Knudsen Olav Langmyr Anne Friederike Borchert Victoria Stornes Moen Ove HetlandSammendrag
Det er ikke registrert sammendrag
Forfattere
Vindhya Basnayaka Jayanga T. Samarasinghe Miyuru Gunathilake Nitin Muttil Dileepa C. Hettiarachchi Amila Abeynayaka Upaka RathnayakeSammendrag
River meandering and anabranching have become major problems in many large rivers that carry significant amounts of sediment worldwide. The morphodynamics of these rivers are complex due to the temporal variation of flows. However, the availability of remote sensing data and geographic information systems (GISs) provides the opportunity to analyze the morphological changes in river systems both quantitatively and qualitatively. The present study investigated the temporal changes in the river morphology of the Deduru Oya (river) in Sri Lanka, which is a meandering river. The study covered a period of 32 years (1989 to 2021), using Landsat satellite data and the QGIS platform. Cloud-free Landsat 5 and Landsat 8 satellite images were extracted and processed to extract the river mask. The centerline of the river was generated using the extracted river mask, with the support of semi-automated digitizing software (WebPlotDigitizer). Freely available QGIS was used to investigate the temporal variation of river migration. The results of the study demonstrated that, over the past three decades, both the bend curvatures and the river migration rates of the meandering bends have generally increased with time. In addition, it was found that a higher number of meandering bends could be observed in the lower (most downstream) and the middle parts of the selected river segment. The current analysis indicates that the Deduru Oya has undergone considerable changes in its curvature and migration rates.
Forfattere
Miyuru GunathilakeSammendrag
Det er ikke registrert sammendrag
Sammendrag
Satellite Rainfall Products (SRPs) are now in widespread use around the world as a better alternative for scarce observed rain gauge data. Upon proper analysis of the SRPs and observed rainfall data, SRP data can be used in many hydrological applications. This evaluation is very much necessary since, it had been found that their performances vary with different areas of interest. This research looks at the three prominent river basins; Malwathu, Deduru, and Kalu of Sri Lanka and evaluates six selected SRPs, namely, IMERG, TRMM 3B42, TRMM 3B42-RT, PERSIANN, PERSIANN-CCS, PERSIANN-CDR against 15+ years of observed rainfall data with the use of several indices. Four Continuous Evaluation Indices (CEI) such as Root Mean Square Error (RMSE), Percentage Bias (PBIAS), Pearson’s Correlation Coefficient (r), and Nash Sutcliffe Efficiency (NSE) were used to evaluate the accuracy of SRPs and four Categorical Indices (CI) namely, Probability of Detection (POD), Critical Success Index (CSI), False Alarm Ratio (FAR) and Proportion Correct (PC) was used to evaluate the detection and prediction accuracy of the SRPs. Then, the Mann–Kendall Test (MK test) was used to identify trends in the datasets and Theil’s and Sens Slope Estimator to quantify the trends observed. The study of categorical indicators yielded varying findings, with TRMM-3B42 performing well in the dry zone and IMERG doing well in the wet zone and intermediate zone of Sri Lanka. Regarding the CIs in the three basins, overall, IMERG was the most reliable. In general, all three basins had similar POD and PC findings. The SRPs, however, underperformed in the dry zone in terms of CSI and FAR. Similar findings were found in the CEI analysis, as IMERG gave top performance across the board for all four CEIs in the three basins. The three basins’ overall weakest performer was PERSIANN-CCS. The trend analysis revealed that there were very few significant trends in the observed data. Even when significant trends were apparent, the SRP projections seldom captured them. TRMM-3B42 RT had the best trend prediction performance. However, Sen’s slope analysis revealed that while the sense of the trend was properly anticipated, the amplitude of the prediction significantly differed from that of the observed data.
Forfattere
Jayanga T. Samarasinghe Vindhya Basnayaka Miyuru Gunathilake Hazi M. Azamathulla Upaka RathnayakeSammendrag
The application of numerical models to understand the behavioural pattern of a flood is widely found in the literature. However, the selection of an appropriate hydraulic model is highly essential to conduct reliable predictions. Predicting flood discharges and inundation extents are the two most important outcomes of flood simulations to stakeholders. Precise topographical data and channel geometries along a suitable hydraulic model are required to accurately predict floods. One-dimensional (1D) hydraulic models are now replaced by two-dimensional (2D) or combined 1D/2D models for higher performances. The Hydraulic Engineering Centre’s River Analysis System (HEC-RAS) has been widely used in all three forms for predicting flood characteristics. However, comparison studies among the 1D, 2D to 1D/2D models are limited in the literature to identify the better/best approach. Therefore, this research was carried out to identify the better approach using an example case study of the Kelani River basin in Sri Lanka. Two flood events (in 2016 and 2018) were separately simulated and tested for their accuracy using observed inundations and satellite-based inundations. It was found that the combined 1D/2D HEC-RAS hydraulic model outperforms other models for the prediction of flows and inundation for both flood events. Therefore, the combined model can be concluded as the better hydraulic model to predict flood characteristics of the Kelani River basin in Sri Lanka. With more flood studies, the conclusions can be more generalized.
Forfattere
Imiya M. Chathuranika Miyuru Gunathilake Pavithra K. Baddewela Erandi Sachinthanie Mukand S. Babel Sangam Shrestha Manoj K. Jha Upaka S. RathnayakeSammendrag
In the present study, the streamflow simulation capacities between the Soil and Water Assessment Tool (SWAT) and the Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS) were compared for the Huai Bang Sai (HBS) watershed in northeastern Thailand. During calibration (2007–2010) and validation (2011–2014), the SWAT model demonstrated a Coefficient of Determination (R2) and a Nash Sutcliffe Efficiency (NSE) of 0.83 and 0.82, and 0.78 and 0.77, respectively. During the same periods, the HEC-HMS model demonstrated values of 0.80 and 0.79, and 0.84 and 0.82. The exceedance probabilities at 10%, 40%, and 90% were 144.5, 14.5, and 0.9 mm in the flow duration curves (FDCs) obtained for observed flow. From the HEC-HMS and SWAT models, these indices yielded 109.0, 15.0, and 0.02 mm, and 123.5, 16.95, and 0.02 mm. These results inferred those high flows were captured well by the SWAT model, while medium flows were captured well by the HEC-HMS model. It is noteworthy that the low flows were accurately simulated by both models. Furthermore, dry and wet seasonal flows were simulated reasonably well by the SWAT model with slight under-predictions of 2.12% and 13.52% compared to the observed values. The HEC-HMS model under-predicted the dry and wet seasonal flows by 10.76% and 18.54% compared to observed flows. The results of the present study will provide valuable recommendations for the stakeholders of the HBS watershed to improve water usage policies. In addition, the present study will be helpful to select the most appropriate hydrologic model for humid tropical watersheds in Thailand and elsewhere in the world.
Sammendrag
Climate change is a serious and complex crisis that impacts humankind in different ways. It affects the availability of water resources, especially in the tropical regions of South Asia to a greater extent. However, the impact of climate change on water resources in Sri Lanka has been the least explored. Noteworthy, this is the first study in Sri Lanka that attempts to evaluate the impact of climate change in streamflow in a watershed located in the southern coastal belt of the island. The objective of this paper is to evaluate the climate change impact on streamflow of the Upper Nilwala River Basin (UNRB), Sri Lanka. In this study, the bias-corrected rainfall data from three Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCPs): RCP4.5 and RCP8.5 were fed into the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model to obtain future streamflow. Bias correction of future rainfall data in the Nilwala River Basin (NRB) was conducted using the Linear Scaling Method (LSM). Future precipitation was projected under three timelines: 2020s (2021–2047), 2050s (2048–2073), and 2080s (2074–2099) and was compared against the baseline period from 1980 to 2020. The ensemble mean annual precipitation in the NRB is expected to rise by 3.63%, 16.49%, and 12.82% under the RCP 4.5 emission scenario during the 2020s, 2050s, and 2080s, and 4.26%, 8.94%, and 18.04% under RCP 8.5 emission scenario during 2020s, 2050s and 2080s, respectively. The future annual streamflow of the UNRB is projected to increase by 59.30% and 65.79% under the ensemble RCP4.5 and RCP8.5 climate scenarios, respectively, when compared to the baseline scenario. In addition, the seasonal flows are also expected to increase for both RCPs for all seasons with an exception during the southwest monsoon season in the 2015–2042 period under the RCP4.5 emission scenario. In general, the results of the present study demonstrate that climate and streamflow of the NRB are expected to experience changes when compared to current climatic conditions. The results of the present study will be of major importance for river basin planners and government agencies to develop sustainable water management strategies and adaptation options to offset the negative impacts of future changes in climate.
Sammendrag
Det er ikke registrert sammendrag