Field research on the performance of various drainage materials in Lithuania
Abstract Field evaluation of the performance of a drainage system or of various drainage materials is a long-lasting research, very often with disappointing results. These disappointing results stem either from a too wide a spread of the field data, or one or more necessary parameters which were not measured, or an insufficient knowledge of the flow occurrence in the vicinity of the drain resulting in a wrong interpretation and evaluation of the research findings. Yet, a correct evaluation of the performance of a drainage system is of primary importance to ascertain the real value of a drainage system or to compare various drainage materials. As a result of the wide spread of field data within a measuring season, a large amount of data from several seasons is required to obtain reliable results. From discharge and total head loss measurements a second-degree polynomial results which only permits a determination of whether the design criteria are met. The similarity with Hooghoudt’s equation allows the determination of soil hydraulic conductivity and the equivalent depth of the impervious layer. With this data the drain spacing can be checked. Too wide a spacing can be the cause of malfunctioning of a drainage system, but the drainage materials can also affect its performance. To evaluate or compare drainage materials it is necessary to measure the so-called approach-flow head loss in the vicinity of the drain. The relationship between discharge and approach-flow head loss should theoretically be linear and the regression coefficient gives the approach-flow resistance. However, the relationship depends to a large extent on the approach-flow occurrence in the vicinity of the drain. For non-linear relationships, the approach-flow resistance can be estimated from the slope of the tangent line, which tends to a constant value at greater discharges for flow patterns covering the whole drain circumference. The approach-flow resistance depends on the hydraulic conductivity of the soil and does not permit a direct comparison of various drainage materials. Therefore, the approach-flow constant or the dimensionless approach-flow resistance is calculated. This parameter is related to the material itself and to the installation conditions reflected in the hydraulic conductivity of the trench backfill. Consequently the comparison of the various drainage materials includes the trench backfill. The approach-flow head loss fraction is that part of the total head loss which is dissipated by the approach-flow. The relationship between approach-flow head loss and total head loss should theoretically be and is, indeed, linear so that the slope of the regression line gives the approach-flow head loss fraction. This parameter combines the influence of drainage material and flow pattern so that real flow situations in the vicinity of the drain, which are not necessarily the same for all materials, can be compared.
Modeling Agricultural Drainage Hydraulic Nets
A review on mathematical models available in the literature to design and evaluate agricultural drainage hydraulic nets is presented, including open ditch and buried pipe alternatives, for steady state and no steady state soil water flows, homogeneous and stratified soil profiles and smooth and corrugated drainage pipes. 
Effective drainage pipe radius effects on drainage performance is considered, based on its perforation density and distribution, as it affects pipe weight bearing strength and pipe deformation intensity. Also, quantitative considerations on perforation density upon water flow resistance into the drain pipe are analyzed.
Natural Radioactivity of Intrusive-Metamorphic and Sedimentary Rocks of the Balkan Mountain Range (Serbia, Stara Planina)
Stara Planina (also known as the Balkan mountain range) is known for numerous occurrences and deposits of uranium and associated radionuclides. It is also famous for its geodiversity. The geologic framework is highly complex. The mountain is situated between the latitudes of 43° and 44° N and the longitudes from 22°16′ to 23°00′ E. Uranium exploration and radioactivity testing on Stara Planina began back in 1948. Uranium has also been mined in the zone of Kalna, within the Janja granite intrusive. The naturally radioactive geologic units of Stara Planina are presented in detail in this paper. The main sources of radioactivity on Stara Planina can be classified as: 1. Granitic endogenous—syngenetic–epigenetic deposits and occurrences; 2. Metamorphogenic—syngenetic; and 3. Sedimentary, including occurrences of uranium deposition and fluctuation caused by water in different types of sedimentary rocks formed in a continental setting, which could be classified under epigenetic types. The area of Stara Planina with increased radioactivity (higher than 200 cps), measured by airborne gamma spectrometry, is about 380 square kilometers. The highest values of measured radioactivity and uranium grade were obtained from a sample taken from the Mezdreja uranium mine tailing dump, where 226Ra measures 2600 ± 100 Bq/kg and the uranium grade is from 76.54 to 77.65 ppm U. The highest uranium (and lead) concentration, among all samples, is measured in graphitic schist with high concentrations of organic (graphitic) material from the Inovska Series—99.47 ppm U and 107.69 ppm Pb. Thorium related radioactivity is the highest in granite samples from the Janja granite in the vicinity of the Mezdreja granite mine and the Gabrovnica granite mine tailing dump, and it is the same—250 ± 10 Bq/kg for 232Th, while the thorium grade varies from 30.82 to 60.27 ppm Th. In gray siltstones with a small amount of organic material, the highest radioactivity is related to potassium—2080 ± 90 Bq/kg for 40K.