Hydraulic modeling of a distributary channel of Athabasca Valles, Mars, using a high‐resolution digital terrain model

Abstract

Estimating magnitudes of flow rates in outflow channels has a central role in developing understanding of the paleohydrology of Mars. The typical approach to flow estimation is to identify geomorphic features, which indicate bankfull levels, and then use a hydraulic model to convert these levels into flow rates. Data constraints have meant that important assumptions about model equations, boundary conditions and parameter values have been necessary. In this paper, we use a high‐resolution digital terrain model derived from NASA's Mars Reconnaissance Orbiter Context Camera stereopair imagery to develop a finer resolution step backwater hydraulic model than previously attempted. Furthermore, the data facilitate a more critical, more formal and broader assessment of this type of model than has previously been attempted. A distributary channel of Athabasca Valles is used as a case study. The median bankfull flow estimate was 39,000 m3 s−1, although estimates range up to 140,000 m3 s−1 depending on the assumptions employed. The principal uncertainties stem from assumptions about bankfull levels and downstream boundary conditions; and assumptions about the friction coefficient, criticality of flow, expansion and contraction losses, and geometric details of the channel are also important under certain conditions. Examination of additional DTMs further downstream would permit the analysis to be extended to hydraulic control sections that provide better‐known boundary conditions, hence improving flow estimates. It is concluded that new‐generation DTM data provide opportunity for deeper insight into the challenges and opportunities for modeling the paleohydrology of Mars, although further work is needed to achieve satisfactory levels of confidence.

Pressurized groundwater outflow experiments and numerical modeling for outflow channels on Mars

“…The model of Manga [] produces discharges of 0.5 to 2.5 ×10 6 m 3 /s for Athabasca Valles (Figure d), which corresponds with peak‐discharge estimates of 1–2 ×10 6 m 3 /s based on bankfull discharge [ Burr et al , ]. Improved methods for discharge estimates based on hydrodynamic models using high‐resolution elevation models provide discharges of the same order of magnitude [ McIntyre et al , ]. In his model, Manga [] simulates one large fissure that reaches to the base of a 3 km deep aquifer; in contrast within our model, the fissures are only present in the confining cryosphere on top the aquifer.…”

“…On the other hand, discharge estimates based on bankfull channel dimensions [e.g., Burr et al , ] tend to overestimate discharge required as the process of incision is not taken into account (i.e., incised river valleys are never filled to the brim). Discharge estimates based on the late‐stage channels [e.g., Leask et al , ] or hydraulic modeling based on the final morphology [e.g., McIntyre et al , ] may underestimate an early discharge peak that is responsible for a large part of the incision. For rapid incisive events with an early peak discharge, the final valley width (and not channel) may provide a better estimate of the peak discharge [ Marra et al , ].…”

Canyon formation constraints on the discharge of catastrophic outburst floods of Earth and Mars

“…Paleohydrologists mostly use two methods to infer discharge from canyon observations: (1) they calculate the required flow depth to initiate motion of the observed sediment sizes through a Shields stress criterion [e.g., O'Connor , ; Lamb et al ., , ] or (2) they assume that observed channels or canyons were filled to the brim (brimful assumption) [e.g., Baker and Milton , ; Carr , ; Robinson and Tanaka , ; Komatsu and Baker , ; McIntyre et al ., ]. Initial motion and brimful assumptions provide conservative lower and upper bounds on flow discharge, respectively, constraining its value with an uncertainty of many orders of magnitude.…”

Hydraulic modeling of the tributary and the outlet of a Martian paleolake located in the Memnonia quadrangle

“…Several estimates have been derived of paleodischarge rates in the tributaries and/or the outlets of Martian paleolakes, valley networks, or outflow channels [e.g., Carr , ; Komar , , ; Goldspiel and Squyres , ; Komatsu and Baker , ; Williams et al , ; Malin and Edgett , ; Burr , ; Wilson et al , ; Howard et al , ; Irwin et al , ; Jaumann et al , ; Kleinhans , ; Andrews‐Hanna and Phillips , ; Keszthelyi et al , ; Leask et al , ; Kraal et al , ; Wilson et al , ; Hoke et al , ; McIntyre et al , ]. Several techniques may be used to reconstruct the water discharge, depth, and velocity in ancient riverbeds and lakes.…”