qertrc.blogg.se

Thus, this large early autumn rain event with low isotopic values (δ 18O, δD provided an excellent natural tracer. These early events, especially the 127 mm April event, had low stable water isotope values compared with later rains during June and July and average winter precipitation. During autumn 2007, a large (127 mm drought-breaking rain occurred in April followed by significant May rains most of this April and May precipitation occurred prior to the initiation of stream flow in late May. In this Mediterranean climate with strong summer moisture deficits, several significant rainfalls are required to generate soil through flow and stream flow. The significance and lag-time of deep through flow: an example from a small, ephemeral catchment with contrasting soil types in the Adelaide Hills, South Australiaĭirectory of Open Access Journals (Sweden)įull Text Available The importance of deep soil-regolith through flow in a small (3.4 km 2 ephemeral catchment in the Adelaide Hills of South Australia was investigated by detailed hydrochemical analysis of soil water and stream flow during autumn and early winter rains. This analysis indicates that when estimating total cumulative infiltration in coarse‐grained ephemeral stream channels, consideration of the transient infiltration at the onset of streamflow will improve predictions of the total volume of infiltration that may become groundwater recharge. Cumulative infiltration error for typical streamflow events of about 8 hours in duration in is about 90%. Cumulative infiltration error for the simulated streamflow events ranged from 9 to 25%. Cumulative infiltration during the transient period represented 10 to 26% of the total cumulative infiltration, with an average contribution of approximately 18%. The duration of simulated transient infiltration ranged from 1.8 to 20 hours, compared with steady state flow periods of 231 to 307 hours. Simulated and measured transient infiltration rates at the onset of streamflow were about two to three orders of magnitude greater than steady state infiltration rates. Water content, temperature, and piezometric measurements from 2.5‐m vertical profiles within the alluvial sediments were used to constrain a variably saturated water flow and heat transport model. Simulations of infiltration during three ephemeral streamflow events in a coarse‐grained alluvial channel overlying a less permeable basin‐fill layer were conducted to determine the relative contribution of transient infiltration at the onset of streamflow to cumulative infiltration for the event.

Relative contributions of transient and steady state infiltration during ephemeral streamflowīlasch, Kyle W. In absolute terms, the estimated indirect recharge varies from 80 to 30 mm/a with the main uncertainty in these values stemming from uncertainty in the catchment-scale hydraulic properties. In relative terms, indirect recharge decreases almost linearly away from the mountain front, both in discrete monitored events as well as in the long-term average. We find that, following episodic streamflow events down a predominantly dry channel system, groundwater head fluctuations are controlled by pressure redistribution operating at three time scales from vertical flow (days to weeks), transverse flow perpendicular to the stream (weeks to months), and longitudinal flow parallel to the stream (years to decades). The technique is demonstrated using a new, and globally unparalleled, set of groundwater observations from an ephemeral stream catchment located in NSW, Australia. By accounting for the recession characteristics of a groundwater hydrograph, we present a simple but powerful new water table fluctuation approach to quantify focused, indirect recharge over both long term and event time scales. Here we develop a generalized conceptual model for understanding water table and groundwater head fluctuations due to recharge from episodic events within ephemeral streams. However, there is a global paucity of data for understanding and quantifying this process and transferable techniques for quantifying groundwater recharge in such contexts are lacking. The dominant process for dryland groundwater recharge is thought to be as focused, indirect recharge from ephemeral stream losses. Understanding and managing groundwater resources in drylands is a challenging task, but one that is globally important. Understanding and quantifying focused, indirect groundwater recharge from ephemeral streams using water table fluctuationsĬuthbert, M.