OUCC Proceedings 11 (1983)

An Estimate of the Palaeodischarge of Cueva Culiembro, Asturias, Northern Spain 

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Steven Gale

Cueva Culiembro (43 15' 30" N, 1 11' 50" W with reference to the Madrid meridian) is a former resurgence cave which, as a result of the incision of the Rio Cares, now lies in the side of the Cares gorge about 30 m above the present resurgence of Fuente Culiembro. The outlet to the cave is largely phreatic in form. At some stage in its development the passage was almost totally infilled by clast-supported cobble-grade fluvial deposits, although this fill has been largely removed by subsequent stream action and now remains only as a carbonate-cemented terrace on either side of the passage. In the roof of the passage can be found solutional scallops. If these can be regarded as having developed during a period when little or no sediment existed in the passage, then the scallops may be used to give an indication of discharge during the period of phreatic development of the cave. This assumption is probably not unreasonable given that the present deposits appear to represent a single sediment input which probably either choked the passage and/or was rapidly re-excavated.

The conditions under which scallops develop has been investigated by numerous workers (see, for example, Allen, 1971; Goodchild and Ford, 1971; Blumberg and Curl, 1974), a number of whom have demonstrated that scallop form is hydraulically-controlled. Under conditions of uniform, steady-state flow, it appears that scallops develop at a stable scallop Reynolds number (Re*), where

(1)

in which = mean boundary-shear velocity, λ = mean scallop wavelength; ρf = fluid density; and μ = fluid dynamic viscosity. Published estimates of mean Re* range between 1000 and 3180 (Blumberg and Curl, 1974, 742; Thomas, 1979; Gale, 1984, Hsu et al., 1979), and all these values fall within the expected laminar-turbulent transition phase of ca. 1000-3000. Consequently, Blumberg and Curl's (1974, 742) estimate of Re* = 2220 will be used in subsequent calculations, since this lies approximately in the middle of the laminar-turbulent transition range, and since it is perhaps the most reliable estimate of the stable value of Re* .

 was established in Cueva Culiembro by measuring scallop wavelength along the maximum length in a streamwise direction, taking the mean of 26 values. Having obtained , from which may be calculated using equation (1), assuming the conduit fluid to be pure water at 10C, the mean flow velocity ( ) in the conduit may be computed by use of Prandtl's universal velocity-distribution equation (as modified by Curl (1974, 3) for use in parallel-walled conduits):

      (2)

in which d = distance between conduit walls; and BL = Prandtl's bed-roughness constant =9.4 for scalloped surfaces (Blumberg and Curl, 1974, 742-744).

Having obtained , and having estimated the conduit cross-section area (a) at the point of measurement to be 15.3 m2, conduit discharge (Q) may be calculated from:

     (3)

The results of these calculations are given below:

 = 0.325 m (s = 0.1074 m)
n = 26

a = 15.3 m2

= 8.9x10~3 m s-1
 = 9.4x10-2 m s-1
Q = 1.4 ms-1

The estimated discharge is of the expected order of magnitude and may be compared with the measured discharge of 0.7 m3 s-1 under low-flow conditions at the modern analogue of the cave, Fuente Culiembro.

References

Allen, J.R. L., 1971. Transverse erosional marks of mud and rock: their physical basis and geological significance. Sediment. Geol. 5, 165-388.

Blumberg, P. N. and Curl, R.L., 1974. Experimental and theoretical studies of dissolution roughness. J. Fluid Mech. 65, 735-751.

Curl, R.L., 1974. Deducing flow velocity in cave conduits from scallops. Bull. Natn. Speleol. Soc. 36, 1-5.

Gale, S.J., 1984. The hydraulics of conduit flow in carbonate aquifers. J. Hydrol. 70, 309-327.

Goodchild, M. F. and Ford, D.C., 1971. Analysis of scallop patterns by simulation under controlled conditions. J. Geol. 79, 52-62.

Hsu, K.S., Locker, F.A. and Kennedy, J. F., 1979. Forced-convection heat transfer from irregular melting wavy boundaries. Rep. Iowa Inst. Hydraul. Res.

Thomas, R.M., 1979. Size of scallops and ripples formed by flowing water. Nature. Lond. 277, 281-283.

Fig. 1. Frequency distribution of scallop wavelengths on the roof of the entrance passage of Cueva Culiembro, Asturias, Northern Spain.