Surface runoff represents a major pathway for pesticide transport from agricultural areas to surface waters. The influence of man-made structures (e.g. roads, hedges, ditches) on surface runoff connectivity has been shown in various studies. In Switzerland, so-called hydraulic shortcuts (e.g. inlets and maintenance manholes of road or field storm drainage systems) have been shown to influence surface runoff connectivity and related pesticide transport. Their occurrence, and their influence on surface runoff and pesticide connectivity have however not been studied systematically. To address that deficit, we randomly selected 20 study areas (average size = 3.5 km2) throughout the Swiss plateau, representing arable cropping systems. We assessed shortcut occurrence in these study areas using three mapping methods: field mapping, drainage plans, and high-resolution aerial images. Surface runoff connectivity in the study areas was analysed using a 2x2 m digital elevation model and a multiple-flow algorithm. Parameter uncertainty affecting this analysis was addressed by a Monte Carlo simulation. With our approach, agricultural areas were divided into areas that are either directly connected to surface waters, indirectly (i.e. via hydraulic shortcuts), or not connected at all. Finally, the results of this connectivity analysis were scaled up to the national level using a regression model based on topographic descriptors and were then compared to an existing national connectivity model. Inlets of the road storm drainage system were identified as the main shortcuts. On average, we found 0.84 inlets and a total of 2.0 manholes per hectare of agricultural land. In the study catchments between 43 and 74 % of the agricultural area is connected to surface waters via hydraulic shortcuts. On the national level, this fraction is similar and lies between 47 and 60 %. Considering our empirical observations led to shifts in estimated fractions of connected areas compared to the previous connectivity model. The differences were most pronounced in flat areas of river valleys. These numbers suggest that transport through hydraulic shortcuts is an important pesticide flow path in a landscape where many engineered structures exist to drain excess water from fields and roads. However, this transport process is currently not considered in Swiss pesticide legislation and authorisation. Therefore, current regulations may fall short to address the full extent of the pesticide problem. However, independent measurements of water flow and pesticide transport to quantify the contribution of shortcuts and validating the model results are lacking. Overall, the findings highlight the relevance of better understanding the connectivity between fields and receiving waters and the underlying factors and physical structures in the landscape.

This package contains images and videos of active hydraulic shortcuts in agricultural areas of the municipalities of Zürich and Rümlang, Switzerland. More information on hydraulic shortcuts and their relevance for pesticide transport in agricultural areas are provided in the following doctoral thesis: https://doi.org/10.3929/ethz-b-000539927 The pictures and videos in this package are intended to be used for outreach or training of farmers, etc. and can be used freely (creative commons license). The pictures and videos were taken on 13 July 2021 between 17:23h and 17:55h (UTC+2h), a few hours after a large two-day rain event. The precipitation measured at a nearby rain gage (station Affoltern, MeteoSchweiz; 47.427694, 8.517953) equalled 41.5mm on the 12th of July, and 34.7mm on the 13th of July. The images and videos were taken at six different locations. The situations that are visible on these images and videos are described in the following. For each location, latitude and longitude is indicated in brackets (WGS84 coordinate system). - **Location 1** (47.42726, 8.52567): Surface runoff on a farm track. Since the farm track is elevated in the middle, water flows at the left and right edge of the farm track. Only at one specific location surface runoff changes from the left to the right side. - **Location 2** (47.43118, 8.52572): Surface runoff flows along one edge of a farm track. - **Location 3** (47.43580, 8.52877): Surface runoff accumulates on a potato field, flows on a asphalt road, and then into an inlet of the road storm drainage system. - **Location 4** (47.44077, 8.52534): Surface runoff flows from a corn field on an asphalt road, and then into an inlet of the road storm drainage system. - **Location 5** (47.43819, 8.50848): Surface runoff accumulates on a field with bare soil, causing erosion. At the field border with the lowest elevation, surface runoff flows onto a small asphalt road and then for around 180m along this road. Finally, the surface runoff flows into an inlet of the road storm drainage system of a larger asphalt road. - **Location 6** (47.43837, 8.50621): Surface runoff formed on grassland flows into an inlet of the storm road drainage system. This occurs either directly, or via the road.