Łukasz Bąk

Spatial distribution of sediments in Suchedniów reservoir / Rozkład osadów w zbiorniku Suchedniów

Abstract The paper presents measurements of the amount, spatial distribution, grain size structure, density and the content of organic matter in sediments of Suchedniów reservoir. After 33 years of exploitation, the primary volume of the reservoir decreased by 78 thousand m3. Catchment area covered in 45% by forests is 83 km2. Mean annual water flow is estimated at 0.63 m3·s-1. Primary volume of the reservoir was 303 thousand m3 and its surface area - 21.4 ha. The greatest width of the reservoir is 490 m, distance from the river inlet to the dam is 655 m and the length along assumed water course is 740 m. Mean and maximum depths are 1.42 and 4 m, respectively. The analyses of vertical and horizontal distribution of sediments revealed that in the deepest parts of the water body, where depth exceed 2.6 m, only 16% of sediment volume were deposited. In the inlet part of a relative volume of 0.2, 32% of sediment volume were deposited and in the outlet part - 16%. The reservoir accumulates material of a grain size <1.0 mm whose density varies between 2586 and 2758 kg·m-3. Percent of organic parts in sediments ranged from 0.24 to 18.97%. The existing methods of description of sediment distribution in retention reservoirs do not allow for accurate predicting of this distribution. They do not account for many factors affecting the distribution of sediments in reservoirs and for the time of exploitation. None of the dimensionless curves of the Annandale’s nomograph [ANNANDALE 1984] describes the distribution of sediments in Suchedniów Reservoir. The curve closest to the actual distribution curve corresponds to the value dP/dx = 1.2 while for Suchedniów Reservoir dP/dx is 0.0014 (P - wetted perimeter of the reservoir’s cross section, x - distance from the dam). Sediments in vertical profiles have laminar structure and bottom material in layers largely differs in grain size and colour which is an evidence of different conditions of sedimentation in different hydrological periods and exploita STRESZCZENIE W pracy przedstawiono przebieg pomiarów ilości osadów, ich przestrzenny rozkład i skład granulometryczny, ciężar właściwy i zawartość części organicznych w osadach w zbiorniku wodnym Suchedniów. Po 33 latach jego eksploatacji zmniejszenie pojemności pierwotnej zbiornika wyniosło ok. 78 tys. m3. Pole zlewni wynosi 83 km2, a lasy zajmują 45% powierzchni. Średni roczny przepływ wody ocenia się na 0,63 m3·s-1. Pierwotna pojemność zbiornika wynosiła 303 tys. m3, a powierzchnia lustra wody - 21,4 ha. Największa szerokość zalewu wynosi 435 m, długość w linii prostej od zapory do wlotu rzeki do zbiornika 655 m, zaś wzdłuż domniemanego nurtu - 740 m. Średnia głębokość akwenu to 1,42 m, a maksymalna - 4 m. Na podstawie analizy pionowego i poziomego rozmieszczenia osadów stwierdzono, że w najgłębszych partiach akwenu, gdzie głębokość przekraczała 2,6 m, odłożyło się tylko 16% objętości osadów. W części wlotowej akwenu, o objętości względnej 0,2, zdeponowane zostało 32%, a w części wylotowej - 16% objętości namułów. W zbiorniku jest akumulowany materiał o średnicy ziaren <1,0 mm, którego gęstość właściwa zawierała się w przedziale od 2586 do 2758 kg·m-3. Udział części organicznych w namułach wahał się od 0,24 do 18,97%. Istniejące metody opisu rozkładu osadów w zbiornikach retencyjnych nie dają możliwości trafnego prognozowania tego rozkładu. Nie uwzględniają wielu czynników kształtujących rozkład osadów w czaszy zbiornika i czasu eksploatacji. Żadna z krzywych bezwymiarowych nomogramu Annandala [ANNANDALE 1984] nie opisuje rozkładu osadów w zbiorniku Suchedniów. Krzywa nomogramu najbliższa w stosunku do rzeczywistej krzywej rozkładu odpowiada wartości dP/dx = 1,2 (P - obwód zwilżony przekroju poprzecznego zbiornika, x - odległość od zapory), a dla zbiornika Suchedniów dP/dx = 0,0014. Osady mają w profilu pionowym budowę warstwową, a materiał denny w warstwach charakteryzuje się znacznym zróżnicowaniem uziarnienia i barwy, co świadczy o odmiennych warunkach jego sedymentacji w różnych okresach hydrologicznych i warunkach eksploatacji. Ogólnie widoczne jest zmniejszanie się średnicy ziaren osadu zgodnie z kierunkiem przepływu.

Probabilistic model for the annual number of storm overflow discharges in a stormwater drainage system

Abstract The paper presents an attempt to develop a probabilistic model for predicting an annual number of storm overflow discharges. Forecasting the occurrence of an overflow discharge event involved the application of the logistic regression, which does not require the development of complex hydrodynamic catchment models. The performed calculations showed that the logistic regression model can be successfully used to evaluate the performance of the emergency overflow weir. The resultant logit model eliminates the necessity to develop hydrodynamic models, to conduct continuous measurements of the flow intensity in the stormwater drainage system and to collect detailed information on the characteristics of the subcatchments within the analyzed catchment. The hydrodynamic model was used to simulate the annual number of discharges. The analysis of the results demonstrated that they are in the range of stochastic values, which indicates an application-related character of the method.

Statistical models to predict discharge overflow

In the paper, a comparison of prediction results concerning the annual number of discharges of stormwater from the drainage system due to stormwater overflows is depicted. The prediction has been computed by means of storm water management model (SWMM) and probabilistic models. Regarding the probabilistic modelling some simple statistical models such as logit, probit, Gompertz and linear discriminant analysis model have been applied, and as for the hydrodynamic modelling a generator of synthetic rainfall based on the Monte Carlo method has been used. The analyses conducted has shown that logit, probit and Gompertz models give outputs that are comparable with the results of hydrodynamic modelling and are concordant with observations. Whereas the annual number of stormwater discharge predicted by the linear discriminant analysis model is significantly lower than the number obtained by hydrodynamic modelling. The calculations made have confirmed the possibility of using statistical models as an alternative for developing labour-consuming and complex hydrodynamic models. The statistical models can be used successfully to predict the stormwater overflows operation provided that the measurements of rainfall in the catchment and of filling the overflow are available.

Preliminary Assessment of Silting and The Quality of Bottom Sediments in A Small Water Reservoir

Abstract The aim of this study was to assess the degree of silting and pollution of bottom sediments in a small water reservoir Lubianka situated in Starachowice, Świętokrzyskie Province, with selected heavy metals (Pb, Cr, Cd, Cu, Ni, Zn, Fe, Mn, Hg). Catchment basin of the reservoir is forested in 92%. Other parts are covered by estates of detached houses, barren lands and green areas. Bathymetric measurements and analyses of trace elements in bottom sediments were made in 2012. After 28 years of exploitation, reservoirs basin accumulated 43 thousand cubic metres of sediments i.e. 4.7% of its initial volume. Mean annual silting rate was 0.17%. Due to the content of copper and chromium, bottom sediments were classified to the II category (sediments of average pollution) according to geochemical standards. Concentrations of Pb, Cd and Hg in all analysed samples were below geochemical background. In a sample collected at the inlet to the reservoir, the TEL index for chromium was exceeded by 25.6%. In other samples the threshold values of the TEL and PEL indices were not exceeded.