Карта на действащите ВЕЦ в България

петък, 24 януари 2014 г.

Научно изследване доказва, че малките ВЕЦ могат да имат по-разрушителен ефект върху реките дори и от големите язовири

От Адам Redling на 27 юни 2013

Ново пет - годишно проучване е довело изследователи от Oregon State University да заключението, че малките водноелектрически проекти могат да окажат отрицателно въздействие върху околната среда повече от големите язовири , поради кумулативната щетите, които те причиняват , според доклад от университета.

Заключението се базира на изследване на речната системата на река Nu в Китай, на която има много малки водноелектрически проекти поради своята многобройни притоци притоци .

Проучването показва, че по-малките водноелектрически проекти имат тенденция да нарушават потока, рибарството , дивата природа и общностите. Това като цяло се дължи на нарушаване на естествения воден поток.

Докладът оценява, че общият ефект върху местообитанията може да бъде 100 пъти по-тежък от изграждането на малки водноелектрически проекти , за разлика от по-големите си колеги.

 Самият доклад, можете да прочетете ТУК

Abundant small hydropower dams more disruptive that large ones
By on June 27, 2013
A new five-year study has led researchers from Oregon State University to conclude that small hydropower projects can negatively impact the environment more than large dams due to the cumulative damage that they cause, according to a report from the university.
The conclusion was based on research of the Nu River system in China, which supports many small hydroelectric projects because of its expansive number of tributaries.
The study shows that smaller hydroelectric projects have a tendency to disrupt streams, fisheries, wildlife and communities as a whole due to the disruption of natural water flow.
It was estimated that the total effect on habitats can be 100 times more severe from the construction of smaller hydroelectric projects as opposed to their larger counterparts.

Support for low-carbon energy and opposition to new large dams encourages global development of small hydropower facilities. This support is manifested in national and international energy and development policies designed to incentivize growth in the small hydropower sector while curtailing large dam construction. However, the preference of small to large dams assumes, without justification, that small hydropower dams entail fewer and less severe environmental and social externalities than large hydropower dams. With the objective to evaluate the validity of this assumption, we investigate cumulative biophysical effects of small (<50 MW) and large hydropower dams in China's Nu River basin, and compare effects normalized per megawatt of power produced. Results reveal that biophysical impacts of small hydropower may exceed those of large hydropower, particularly with regard to habitat and hydrologic change. These results indicate that more comprehensive standards for impact assessment and governance of small hydropower projects may be necessary to encourage low-impact energy development.

The original review of macropores and water flow in soils by Beven and Germann is now 30 years old and has become one of the most highly cited papers in hydrology. This paper attempts to review the progress in observations and theoretical reasoning about preferential soil water flows over the intervening period. It is suggested that the topic has still not received the attention that its importance deserves, in part because of the ready availability of software packages rooted firmly in the Richards domain, albeit that there is convincing evidence that this may be predicated on the wrong experimental method for natural conditions. There is still not an adequate physical theory linking all types of flow, and there are still not adequate observational techniques to support the scale dependent parameterizations that will be required at practical field and hillslope scales of application. Some thoughts on future needs to develop a more comprehensive representation of soil water flows are offered.

Chao Li, Vijay P. Singh and Ashok K. Mishra
Article first published online: 6 JUN 2013 | DOI: 10.1002/wrcr.20146

[1] River flow synthesizing and downscaling are required for the analysis of risks associated with water resources management plans and for regional impact studies of climate change. This paper presents a probabilistic model that synthesizes and downscales monthly river flow by estimating the joint distribution of flows of two adjacent months conditional on covariates. The covariates may consist of lagged and aggregated flow variables (synthesizing), exogenous climatic variables (downscaling), or combinations of these two types. The joint distribution is constructed by connecting two marginal distributions in terms of copulas. The relationship between covariates and distribution parameters is approximated by an artificial neural network, which is calibrated using the principle of maximum likelihood. Outputs of the neural network yield parameters of the joint distribution. From the estimated joint distribution, a conditional distribution of river flow of current month given the estimation of the previous month can be derived. Depending on the different types of covariate information, this conditional distribution may serve as the “engine” for synthesizing or downscaling river flow sequences. The idea of the proposed model is illustrated using three case studies. The first case deals with synthetic data and shows that the model is capable of fitting a nonstationary joint distribution. Second, the model is utilized to synthesize monthly river flow at four sample stations on the main stream of the Colorado River. Results reveal that the model reproduces essential evaluation statistics fairly well. Third, a simple illustrative example for river flow downscaling is presented. Analysis indicates that the model can be a viable option to downscale monthly river flow as well.

Development and testing of a snow interceptometer to quantify canopy water storage and interception processes in the rain/snow transition zone of the North Cascades, Washington, USA (pages 3243–3256)Kael A. Martin, John T. Van Stan II, Susan E. Dickerson-Lange, James A. Lutz, Jeffrey W. Berman, Rolf Gersonde and Jessica D. Lundquist
Article first published online: 6 JUN 2013 | DOI: 10.1002/wrcr.20271
[1] Tree canopy snow interception is a significant hydrological process, capable of removing up to 60% of snow from the ground snowpack. Our understanding of canopy interception has been limited by our ability to measure whole canopy water storage in an undisturbed forest setting. This study presents a relatively inexpensive technique for directly measuring snow canopy water storage using an interceptometer, adapted from Friesen et al. (2008). The interceptometer is composed of four linear motion position sensors distributed evenly around the tree trunk. We incorporate a trunk laser‐mapping installation method for precise sensor placement to reduce signal error due to sensor misalignment. Through calibration techniques, the amount of canopy snow required to produce the measured displacements can be calculated. We demonstrate instrument performance on a western hemlock (Tsuga heterophylla) for a snow interception event in November 2011. We find a snow capture efficiency of 83 ± 15% of accumulated ground snowfall with a maximum storage capacity of 50 ± 8 mm snow water equivalent (SWE). The observed interception event is compared to simulated interception, represented by the variable infiltration capacity (VIC) hydrologic model. The model generally underreported interception magnitude by 33% using a leaf area index (LAI) of 5 and 16% using an LAI of 10. The interceptometer captured intrastorm accumulation and melt rates up to 3 and 0.75 mm SWE h−1, respectively, which the model failed to represent. While further implementation and validation is necessary, our preliminary results indicate that forest interception magnitude may be underestimated in maritime areas.

Dynamic root distributions in ecohydrological modeling: A case study at Walnut Gulch Experimental Watershed (pages 3292–3305)Gajan Sivandran and Rafael L. Bras
Article first published online: 10 JUN 2013 | DOI: 10.1002/wrcr.20245

[1] Arid regions are characterized by high variability in the arrival of rainfall, and species found in these areas have adapted mechanisms to ensure the capture of this scarce resource. In particular, the rooting strategies employed by vegetation can be critical to their survival. However, land surface models currently prescribe rooting profiles as a function of only the plant functional type of interest with no consideration for the soil texture or rainfall regime of the region being modeled. Additionally, these models do not incorporate the ability of vegetation to dynamically alter their rooting strategies in response to transient changes in environmental forcings or competition from other plant species and therefore tend to underestimate the resilience of these ecosystems. To address the simplicity of the current representation of roots in land surface models, a new dynamic rooting scheme was incorporated into the framework of the distributed ecohydrological model tRIBS+VEGGIE. The new scheme optimizes the allocation of carbon to the root zone to reduce the perceived stress of the vegetation, so that root profiles evolve based upon local climate and soil conditions. The ability of the new scheme to capture the complex dynamics of natural systems was evaluated by comparisons to hourly timescale energy flux, soil moisture, and vegetation growth observations from the Walnut Gulch Experimental Watershed, Arizona. Robust agreement was found between the model and observations, providing confidence that the improved model is able to capture the multidirectional interactions between climate, soil, and vegetation at this site.

Small dams on Chinese river harm environment more than expected
May 29, 2013
(Phys.org) —A fresh look at the environmental impacts of dams on an ecologically diverse and partially protected river in China found that small dams can pose a greater threat to ecosystems and natural landscapes than large dams. Read more at: http://phys.org/news/2013-05-small-chinese-river-environment.html#jCp

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