Variability of herbicide losses from 13 fields to surface water within a small catchment after a controlled herbicide application

Diffuse losses from agricultural fields are a major input source for herbicides in surface waters. In this and in a companion paper, we present the results of a comprehensive field study aimed at assessing the overall loss dynamics of three model herbicides (i.e., atrazine, dimethenamid, and metolachlor) from a small agricultural catchment (2.1 km2) and evaluating the relative contributions of various fields having different soil and topographical characteristics. An identical mixture of the three model herbicides as well as an additional pesticide for identification of a given field were applied within 12 h on 13 cornfields (total area approximately 12 ha), thus ensuring that the herbicides were exposed to identical meteorological conditions. After the simultaneous application, the concentrations of the compounds were monitored in the soils and at the outlets of three subcatchments containing between 4 and 5 cornfields each. Particular emphasis was placed on the two rain events that led to the major losses of the herbicides. The rank orders of herbicide dissipation in the soils and of the compound-specific mobilization into runoff were the same in all three subcatchments and were independent of the field characteristics. In contrast, the field properties caused the relative losses from two subcatchments to differ by up to a factor of 56 during the most important event, whereas compound-specific differences of the three neutral herbicides caused the losses to vary only by a factor of 2 during the same event. The enormous spatial variability was mainly caused by factors influencing the fraction of rain that was lost to surface water by fast transport mechanisms. Thus, the key factors determining the spatially variable herbicide losses were the permeability of the soils, the topography, and the location of subsurface drainage systems. These results illustrate the large potential to reduce herbicide losses by avoiding application on risk areas.     

Traglastberechnung von schlanken Verpreßpfählen in weichen bindigen Böden

Ultimate load capacity of slender injection piles in soft soils. Small diameter driven injection piles are applied as a low cost foundation element for many years. They reach extremly high slenderness and tend to buckling behaviour. Some recent damage cases show that the bearing capacity is frequently overestimated. The design codes do not give evidences for the estimation of the ultimate load capacity in detail. The purpose of this paper is to show a practical method of analysis which includes the essential input parameters of apparent cohesion intercept and pile imperfection as well as the elastoplastic properties of pile material and soil.     

Zum Sicherheitspotential des geotextilbewehrten Gründungspolsters gegenüber Setzungen

Regarding the safety margin of cushion foundation armed with geotextiles in order to reduce settlements. For construction of foundationes in areas with possible local weak zones or cavities often cushion layers armed with geotextiles are applied and considerationes of possible settlements in their safety margin are claimed. In practical experience a simple soil mechanical model with derived calculation was helpful. In the following the soil mechanical model of an idealized conical and cylindrical loosening zone within the cushion layer will be presented and their safety margin will be discussed. Subsequently the possiblility of reducing further settlements by arming the cushion layer with tensile geotextiles is described and calculated by an an approximate method provided by Rafael [2]. A calculation done as example shows a close correlation to observed in‐situ settlements. It has to be taken into consideration that the loosened cushion soil and settlement trough elaborated above will suffer additional settlements where being exposed to static and particularely dynamic loads. For estimating such settlements common calculation methods can be used.