Towards an increase of flash-flood geomorphic effects due to gravel mining and ground subsidence in Nogalte stream (SE Spain, Murcia)

Abstract

Abstract. Transition from endorheic alluvial fan environments to well-channelized fluvial systems in natural conditions may occur in response to base-level fluctuations. However, human-induced changes in semi-arid regions can also be responsible for similar unforeseen modifications. Our results confirm that in-channel gravel mining and aquifer overexploitation over the last 50 years in the case study area have changed the natural stability of the Nogalte stream and, as a result, its geomorphic parameters including channel depth and longitudinal profile have begun to adapt to the new situation. Using interferometric synthetic aperture radar (InSAR) data we obtain maximum values for ground subsidence in the Upper Guadalentín basin of ~ 10 cm yr−1 for the period 2003–2010. In this context of a lowered base level, the river is changing its natural flood model to a more energetic one. A comparison of the 1973 flood event, the most dramatic ever recorded in the area, with the 2012 event, where there was a similar discharge but a sediment load deficit, reveals greater changes and a new flooding pattern and extension. In-channel gravel mining may be responsible for significant local changes in channel incision and profile. This, together with the collateral effects of aquifer overexploitation, can favor increased river velocity and stream power, which intensify the consequences of the flooding. The results obtained here clearly demonstrate an existing transition from the former alluvial pattern to a confined fluvial trend, which may become more pronounced in the future due to the time-lag between the drop in aquifer level and ground subsidence, and introduce a new scenario to be taken into consideration in future natural hazard planning in this area.

Impacts of riverine sand mining on freshwater ecosystems: A review of the scientific evidence and guidance for future research

“…Reduction in the water table level may also impact off‐channel wetlands and tributaries and alter the seasonal flow regimes of rivers (Neal, ). Groundwater abstraction and associated ground subsidence combined with sand mining was identified as a driver of channel incision in the Nogalte stream, southeast Spain (Ortega‐Becerril et al, ). Increased salt water intrusion was also a response to channel incision, with increased intrusion reported in the Kaluganga estuary in Sri Lanka (Ratnayake, Silva, & Kumara, ), the Tweed River in Australia (Rinaldi, Wyżga, & Surian, ), and in the Mekong (Brunier et al, ).…”

“…The degree of channel incision ranged considerably, from 0.5 to 3.5 m (Dang, Umeda, & Yuhi, 2014), up to 10 m (Calle, Alho, & Benito, 2017;Skalski et al, 2016;Moretto et al, 2014;Gumiero, Rinaldi, Belletti, Lenzi, & Puppi, 2015) to over 30 m in the Bachang River in Taiwan (Huang, Liao, Pan, & Cheng, 2014). Substantial channel incision was generally associated with channel narrowing linked to bank erosion due to over steepening and destabilization of banks (Ortega-Becerril, Garzón, Béjar-Pizarro, & Martínez-Díaz, 2016;Campana et al, 2014). The extreme case of 30 m incision was accompanied by the channel narrowing to 1/6 of its original width.…”

Interpolation of GPS and Geological Data Using InSAR Deformation Maps: Method and Application to Land Subsidence in the Alto Guadalentín Aquifer (SE Spain)

“…Ground deformation in the study area was measured using ENVISAT SAR data from [32]. The ENVISAT SAR sensor (C-band) has an average incidence angle of 23 • ; the spatial resolution is 25 m; and its minimum revisit time is 35 days [33].…”