Lowered stability of soil aggregates governed by insufficient organic matter levels has become a major concern in Sri Lanka. Although the use of organic manure with water repellent properties lowers the wetting rates and improves the stability of soil aggregates, its effects on soil hydrophysical properties are still not characterized. Therefore, the objective of this study was to examine the relation of water repellency induced by organic manure amendments to the water entry value and water retention of a Sri Lankan Ultisol. The soil was mixed with ground powders of cattle manure (CM), goat manure (GM), Gliricidia maculata (GL) and hydrophobic Casuarina equisetifolia (CE) leaves to obtain samples ranging from non-repellent to extremely water repellent, in two series. Series I was prepared by mixing GL and CE with soil (5, 10, 25, 50%). Series II consisted of 5% CM, GM, and GL, with (set A) and without (set B) intermixed 2% CE. Water repellency, water entry value, and water retention of samples were determined in the laboratory. Soilwater contact angle increased with increasing organic matter content in all the samples showing positive linear correlations. Although the samples amended with CE showed high soil-water contact angles in series I, set A (without 2% CE) and set B (with 2% CE) in series II did not show a noticeable difference, where >80% of the samples had soilwater contact angles <90°. Water entry value (R2 = 0.83-0.92) and the water retention at 150 cm suction (R2 = 0.69-0.8) of all the samples increased with increasing soil-water contact angles showing moderate to strong positive linear correlations. However, set A (without 2% CE) and set B (with 2% CE) in series II did not differ noticeably. Water entry value of about 60% the samples was <2.5 cm. Mixing of a small amount (2%) of hydrophobic organic matter with commonly used organic manures slightly increased the water repellency of sample soils, however not up to detrimental levels. It did not generate adverse effects on water entry and increased the water retention. It was clear that intermixing of small quantities of hydrophobic organic manure with organic manures commonly used in Sri Lankan agriculture, would not generate unfavorable impacts on soils.
The spatial and temporal patterns of surface water (SW) - groundwater (GW) exchange are significantly affected by riverbed silting, clogging or erosion processes, by altering the thickness and hydraulic conductivity of riverbed sediments. The duration of SW-GW exchange is controlled by the drainage and infiltration resistance of river bottom sediments (e.g. Andrássy et al., 2012). Generally, these two parameters primarily depend on the hydraulic conductivity and on the thickness of clogged layer. In this study the flow processes between GW and SW were modeled by model TRIWACO for different infiltration resistance and drainage resistance of riverbed sediments. The model area is situated on the Rye Island, which is a lowland area with very low slope. In this area a channel network was built up, where the flow conditions are controlled by water-gates. Because of the low slope and the system of water gates built on the channels, the riverbeds are influenced by intensive clogging processes. First, the applicability of model TRIWACO in the study area was tested by modelling the response of GW on SW level fluctuation. It was simulated, how the regulation of water level and flow direction in the channels influence the GW level, especially in extreme hydrological conditions (drought/flood), and if the GW flow direction and GW level change as it was expected. Next, the influence of channel network silting up on GW-SW interaction was modeled. The thickness of riverbed sediments was measured and their hydraulic conductivity from disturbed sediment samples was evaluated. The assessed hydraulic conductivity was used to calculate the infiltration resistance and the drainage resistance of riverbed sediments in the study area. Then, the GW level and flow direction was simulated for different infiltration resistance and drainage resistance of sediments.
This paper deals with optimisation and acceleration of the clarification process. It was established that both these objectives are closely inter-related and can be accomplished by the formation of aggregates with a high agitation intensity until the flocculation optimum is reached. This is a new method of formation of aggregates which is called the Inline High Density Suspension (IHDS) formation process. Further, under the IHDS process the aggregates are formed with a single root-mean-square velocity gradient G valu e fl >> 50 s-1. It was also established that the process of formation of aggregates (expressed by residual e of the observed determinant) passes through a minimum. This minimum is considered to be th occulation optimum. Furthermore, the agitation intensity (G ) was found to be the inherent means influencing compactness and thereby density of the aggregates formed. This proves the vital role of agitation intensity on the morphological and physical properties of aggregates formed. The resultant aggregates formed by the IHDS process are very compact, dense and homogeneous in their size, shape, volume and inner structure. Last but not least, the IHDS process applied to the HR-CSAV type sludge blanket clarifier facilitated its high attainable upflow velocity above of 25 m h-1. and Článek se zabývá optimalizací a zrychlením čiřícího procesu. Bylo zjištěno, že oba tyto cíle spolu úzce souvisí a může jich být dosaženo tvorbou agregátů probíhající s vysokou intenzitou míchání pomocí procesu Inline High Density Suspension (IHDS). Za podmínek metody IHDS probíhá tvorba agregátů při vysokých rychlostních gradientech G proc , že in >> 50 s-1, a to až do ukončení jejich tvorby ve flokulačním optimu. Bylo prokázáno, že tvorba agregátů hází minimem, které je možné považovat za flokulační (agregační) optimum. Dále bylo zjištěno tenzita míchání (G ) je přirozeným prostředkem ovlivňujícím kompaktnost a tím rovněž hustotu vytvořených agregátů. Výsledné agregáty vytvořené IHDS procesem jsou velmi kompaktní, husté s homogenní velikostní distribucí, mají pravidelný tvar a uspořádanou vnitřní strukturu. Aplikace IHDS procesu v HR-ČSAV čiřičích umožňuje jejich provoz při vzestupné rychlosti přesahující 25 m h-1 a celkové době zdržení necelých 12 minut.
The follow up research into the IHDS process was carried out with a Couette device. The outcome of this study provides a comprehensive understanding of the effect that both the agitation intensity and the agitation time have on the kinetics and the mechanism of the aggregation process. The results obtained confirm the very favourable influence of high agitation intensity for the formation of more compact and dense aggregates than those formed by the accustomed flocculation conditions with low agitation intensity. This research also proved that the agitation intensity and time are the inherent means profoundly influencing the properties of the resultant aggregates such as their size, shape, density and homogeneity. Further, it was confirmed that the aggregation process passes through a minimum. Furthermore, it was verified that the aggregation process takes place in four consecutive phases, namely a) the phase of formation, b) the phase of compaction, c) the phase of a steady (equilibrium) state and d) most probably the phase of inner restructuring. The pattern of the aggregates development in these phases remains the same irrespective of the magnitude of the velocity gradient applied but the time at which these phases are completed is velocity gradient dependent. Last but not least this study proved that the dimensionless product Ca = G T = const. has no general validity. and Výzkum tvorby agregátů metodou IHDS pokračoval s Couettovým typem flokulačního zařízení. Výsledek této studie umožňuje porozumět vlivu intenzity a času míchání na kinetiku a mechanismus agregačního procesu. Získané výsledky potvrzují velmi příznivý vliv vysoké intenzity míchání na tvorbu kompaktnějších a hustších agregátů než jsou ty vytvořené běžnými flokulačními podmínkami s nízkou intenzitou míchaní. Tento výzkum také potvrdil, že intenzita míchání ve spojení s časem je přirozeným prostředkem výrazně ovlivňujícím vlastnosti výsledných agregátu jako je jejich rozměr, tvar, hustota a homogennost. Dále bylo potvrzeno, že agregační proces probíhá ve čtyřech následných fázích. Jedná se o: a) fázi tvorby, b) fázi zhutňování, c) fázi rovnovážného stavu a d) s největší pravděpodobností fázi vnitřní restrukturalizace. Struktura agregátů vytvořených v jednotlivých fázích je obdobná bez ohledu na velikost použitého rychlostního gradientu, ale čas potřebný k ukončení těchto fází je závislý na velikosti použitého rychlostního gradientu. V neposlední řadě tato studie potvrdila, že bezrozměrné kritérium Ca = G T = = konst. nemá všeobecnou platnost.
On the basis of the results of calibration of current meters at water of varying temperatures, a hypothesis that water temperature influences measured water velocities was formulated. The analysis of our long-term data showed that the water temperature does have an influence on measured water velocity. This influence can be taken into account for practical purposes as a contribution to the uncertainty of measurements. The influence depends on the type of current meter propeller. This paper presents results obtained for the Ott C-2 current meter with propellers of the types 1, 2, 3, 5 and 6. Our analysis showed that the uncertainty is equal or less than 5% for measurements carried out in water with temperatures above 8°C. The differences between measured water velocities for water temperatures 5°C and 20°C reached maximum 6% (depending on the propeller) in a slowly flowing water (rotational frequency n = 1 s-1 ). For rotational velocity n ≥ 2 s-1 the differences between velocities measured at water temperatures 5 and 20°C were mostly under 3%. The less influenced propeller is of type 3 for which the uncertainty of measurement does not reach 5% even for water temperature 1ºC if the rotational frequency is bigger than 0.7 s-1 .