Use of geological mapping tools to improve the hydraulic performance of SuDS

Abstract

Most cities in Denmark are situated on low permeable clay rich deposits. These sediments are of glacial origin and range among the most heterogeneous, with hydraulic conductivities spanning several orders of magnitude. This heterogeneity has obvious consequences for the sizing of sustainable urban drainage systems (SuDS). We have tested methods to reveal geological heterogeneity at field scale to identify the most suitable sites for the placement of infiltration elements and to minimize their required size. We assessed the geological heterogeneity of a clay till plain in Eastern Jutland, Denmark measuring the shallow subsurface resistivity with a geoelectrical multi-electrode system. To confirm the resistivity data we conducted a spear auger mapping. The exposed sediments ranged from clay tills over sandy clay tills to sandy tills and correspond well to the geoelectrical data. To verify the value of geological information for placement of infiltration elements we carried out a number of infiltration tests on geologically different areas across the field, and we observed infiltration rates two times higher in the sandy till area than in the clay till area, thus demonstrating that the hydraulic performance of SuDS can be increased considerably and oversizing avoided if field geological heterogeneity is revealed before placing SuDS.

Detailed Geophysical Mapping and Hydrogeological Characterisation of the Subsurface for Optimal Placement of Infiltration-Based Sustainable Urban Drainage Systems

“…The percolation rate of clay till varies from 2.7 × 10 −7 m/s to 2 × 10 −4 m/s. These results are in accordance with the results obtained by Bockhorn et al [38]. The variation in percolation rates for the clay till is most likely due to soil structure, the CaCO3 boundary and earthworm burrows.…”

“…Geosciences 2020, 10, x FOR PEER REVIEW 3 of 19 [37,38]. Therefore, it would be advantageous if more generic similarities between geoelectric resistance, lithology, geotechnical in situ vane tests and infiltration capacity could be achieved covering larger areas.…”

“…To the author's knowledge, few Danish studies have tried to establish a quantitative and/or qualitative relationship between resistivity and infiltration capacity, lithology and geotechnical tests based on large-scale data sampling. Until now, only site-specific geophysical mapping has been used to investigate the best placement of SUDSs as well as their infiltration performance in Denmark [37,38].…”