Analysis of environmental flow requirements for macroinvertebrates in a creek affected by urban drainage (Prague metropolitan area, Czech Republic)

The habitat suitability index and environmental flow requirements were assessed for ten species of macroinvertebrates in a 2 km length section of the urban Botič creek (average flow 0.4 m³ s⁻¹) in Prague. Botič creek has been affected by two combined sewer overflows (CSO). Spring, summer and fall seasonal environmental flow requirements were identified using the Physical HABitat SIMulation System (PHABSIM) approach for the whole macroinvertebrate community: Spring – optimal flow 0.32–0.38 m³ s⁻¹, minimal flow 0.20–0.21 m³ s⁻¹ and maximal acceptable flow 0.91–0.93 m³ s⁻¹; Summer - optimal flow 0.42–0.45 m³ s⁻¹, minimal flow 0.19–0.21 m³ s⁻¹ and maximal acceptable flow 0.95–1.00 m³ s⁻¹; Fall - optimal flow 0.38–0.48 m³ s⁻¹, minimal flow 0.22–0.23 m³ s⁻¹ and maximal acceptable flow 0.95–0.98 m³ s⁻¹. The seasonal variability of environmental flow for all three categories is approximately 10%. Environmental flow requirements of the studied species and their life stages vary with depth, velocity and bottom substratum. Due to inflow from the CSOs, the optimal and maximal acceptable flow are not maintained and the maximal flow is exceeded by more than twice its value. Although the Instream Flow Incremental Methodology (IFIM) was primarily designed for large impounded rivers, the study proved its applicability in small streams affected by urbanization and urban drainage.