Interbasin flow revisited: The contribution of local recharge to high-discharge springs, Death Valley, CA

Abstract

Springs in the Furnace Creek area (Texas, Travertine, and Nevares Springs) of Death Valley National Park exhibit high discharge rates and depleted δ 18O VSMOW (∼−13‰) and δD VSMOW (∼−102‰) values. Isotopic depletion of this magnitude and large spring fluxes (∼10,000 L/min) suggests that modern local recharge in the arid Furnace Creek drainage cannot be responsible for spring fluxes. An alternate explanation, interbasin flow, is difficult to envisage due to the stratigraphic and structural relationships of bedrock in intervening ranges, although it is the most common conceptual model for Furnace Creek spring flows. High-flux springs at Furnace Creek nonetheless respond modestly to modern climate in terms of discharge rate and isotopic composition. Hydrographs show a climate response and variations in time-series stable isotope data of widely spaced springs track one another. Small, but measurable quantities of tritium (<0.2 TU) were found at Nevares Spring, also suggesting a component of modern recharge. Thus, whatever the main source of water for these springs may be, there appears to be a subtle, but recent climatic influence. Estimates of flow at nearby mountain springs produce discharge rates per square kilometer of catchment that, by analogy, could support from 20 to 300% of the flow at large Death Valley springs under the current climate. Yet, 14C model ages suggest valley-bottom springs at Furnace Creek (5500–14,500 yr) contain a large component of older water, suggesting that much of the water was recharged during a pluvial period (Younger Dryas?) when net infiltration would have been much higher and isotopically depleted. 14C model ages are also of similar age, or younger, than many ‘up gradient’ waters, rather than being older as would be expected for interbasin flow. Chemical evolution models of solutes are consistent with both local recharge and interbasin transfer from Ash Meadows. However, when considered with isotopic constraints, interbasin flow becomes obviously untenable. Estimates of the thickness of alluvium and semi-consolidated Tertiary units in the Furnace Creek drainage seem to provide adequate storage, confinement, and upward leakage to accommodate current discharge. Thus, although Death Valley is the ultimate discharge location for regional groundwaters in terms of potential, careful study of these springs suggests that most of their flux is supported by local pluvial recharge, suggesting that a careful re-evaluation of the interbasin transfers be conducted on a case-by-case basis. Furthermore, regional flow models that are built on the concept of interbasin flow provide boundary flux conditions for site-scale models for the proposed nuclear waste repository at Yucca Mountain, Nevada. Thus, site-scale models may over-predict the potential transport of waste from the Yucca Mountain facility.