... This field study has shown how an impulse radar ice profiling survey can be used to survey for fresh water in isolated pools under the ice cover of arctic river deltas. ..

Kovacs, A.

Morey, R.M.

English

University of Calgary Journal Hosting

ARCTIC VOL. 32, NO. 2 (JUNE 1979), P. 161-164. Remote Detection Of A Freshwater Pool Off The Sagavanirktok River Delta, Alaska A. KOVACS' and R. M. MOREY2 A recent  paper by Kovacs (1978) discussed  the findings of a  study in  which an impulse radar sounding system was used to detect  water  under ice-covered lakes on  the  North Slope of Alaska. The study revealed that  the  radar system could be used to determine, from the  ice  surface or from a helicopter,  lake ice thickness,  water  depth  under  the  ice,  and  where  the  ice was  in contact with the  lake  bottom. In early May 1978, a pool of fresh water was discovered during impulse radar sounding measurements of sea ice  thickness  near  Howe  Island on the coast of the Sagavanirktok River Delta, Alaska. Its  potential  as a source of potable  water was investigated and is reported  here. The impulse radar profiling system used consisted of an  electronics  console, a graphic recorder and an antenna pulled along the  ice  surface.  The  system and its operational characteristics have been described by Morey, (1974), Campbell and  Orange, (1974) and  Kovacs  and  Morey, (1978). The freshwater pool was discovered during an ice thickness profile run along a section of the 1977-78 winter ice  road. This road began at  the  East Dock in Prudhoe Bay (Fig. 1) and continued  eastwards along the  coast to  the vicinity of Flaxman  Island,  From Heald Point at  the tip of the peninsula on the east side of Prudhoe Bay the road ran in a southeast direction toward Howe Island. On this road section the ice was generally grounded on the shallow delta sediments, and long sections of road crossed gravel bars and beaches. At one location on the road the ice abruptly thickened and a subbottom was detected in the  radar  data. The  graphic record obtained in show in Figure 2. This record is a display of the travel  time of the  radar signal from the  ice  surface to  the  ice/soil,  icelwater and waterhoil interfaces. The watedsoil interface reflection would not be present if sea water of normal salinity existed under  the  ice  as  the electromagnetic energy radiated by the antenna cannot penetrate sea water because of its high conductivity.  Therefore,  the  water  under  the  ice was either fresh or its salinity was low enough to allow the radar signal to propagate through to  the bottom and back. New Hampshire, 03755 'U.S. Army Corps of Engineers Cold Regions Research and  Engineering Laboratory, Hanover, Morey Research Co., B-3  Black Oak Drive, Nashua, New Hampshire, 03060 162 A. KOVACS and R. M. MOREY FIG. 2. Graphic record of the impulse radar signal showing the ice road and freshwater pool cross  section. The time from the ice surface to the black line at the very bottom of the figure is about 40 ns. REMOTE DETECTION FRESHWATER POOL 163 For certain homogeneous materials, such as fresh water and fresh-water ice,  the  radar signal velocity V, of propagation can be calculated from: T.l I- C where c = freespace radar velocity e, = dielectric  constant = 81 for  fresh  water and = '3.2 for  freshwater ice. With the propagation velocity thus  determined,  the  depth  D to an interface can  be  determined from: D = V e y  t . .  (2) where t = travel time to and from the  subsurface  interface. From flight times scaled off the graphic record we determined that  the  ice thickness ranged between 1.70 and 1.75 m on the  east side of the pool and that the  distance from the  ice  surface to the basin bottom was about 2 m. These measurements were verified  by  coring through  the ice near  the  east  side of the pool. Using a  tape  measure, we found that  the  ice  thickness was 1.75 m and the  depth to the bottom of the pool was 1.98 m. An inspection of the  core retrieved during drilling indicated that  the ice had formed from fresh water. Salinity measurements of the melt-water obtained from sections of the ice core revealed salinities from 0.02 to 0.05 part per thousand ("loo). The salinity of the pool water was found to  be 0.15 "loo. This salinity is  well  within public health standards  for  potable  water and  is significantly less than the 1.2 "lo0 salinity of the  tap  water  at  the  Deadhorse camp  where  the  authors  stayed. The general location of the pool was determined by odometer distance measurements made on the ice road from the pool to several bluffs and islands along the  road. Using these  measurements and detailed maps of the  area we located  the pool on the photomosaic shown in Figure 1. This mosaic shows the  west  channel  area of the Sagavanirktok River Delta during spring runoff on 27 June 1970. The pool area, at the tip of the arrow, is shown to be somewhat  circular and its  colour  indicates  that it is filled  with silty water. Figure 1 also  shows the location of a man-made gravel island from which an exploratory oil  well  was drilled during the winter of 1977-78. The  dashed  line represents  the long  haul route used by Rolligons to transport  fresh  water from the  two  lakes, marked  with an X, at  the  south end of the  route to the island drill site.  The  cost of transporting  the  water was about  three hundred and fifty thousand  dollars. Had the drilling rig been supplied from the  freshwater  pool, less expensive truck transport could have been used over the existing ice roads. We measured the effective width of the pool to be -200 m. The aerial photo of the pool shows that it was nearly circular.  Therefore,  the pool  had a  surface area of about 3 1,000 m2. If we assume  that  there was an effective water  depth 1 6 4  A. KOVACS and R. M. MOREY of 1 m during the drilling operation,  then  about 3 1,000 m3 (8.2  million  gallons) of water would have been easily available.  Even half this volume would have been enough to support  the drilling operation. This field study has shown how an impulse radar ice profiling survey  can  be used to survey  for  fresh water in isolated pools under  the  ice  cover of arctic river deltas. It complements the earlier field results of Kovacs (1978) who used impulse radar to detect  free water under  lake  ice on the  North Slope of Alaska. REFERENCES CAMPBELL, K. J. and ORANGE, A. s. 1974. A  continuous  profile of sea  ice  and  freshwater  ice  thickness by impulse  radar.  Polar  Record, 17 (106), p. 30-42. KOVACS, A. and MOREY, R. M. 1978. Radar anisotropy of sea ice due to preferred azimuthal orientation of the  horizontal  c-axis of ice  crystals.  Journal of Geophysical  Research, 83, (C12). KOVACS, A. 1978. Remote detection of water under ice-covered lakes on the North Slope of Alaska.  Arctic, 31(4) p. 448-458. MOREY, R. M. 1974. Continuous  subsurface profiling by impulse  radar.  Proceedings of Engineering Foundation  Conference  on  “Subsurface  Exploration for Underground  Excavation  and  Heavy Construction,”  American  Society of Civil Engineering, N.Y. 

Remote Detection of a Freshwater Pool Off the Sagavanirktok River Delta, Alaska

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Remote Detection of a Freshwater Pool Off the Sagavanirktok River Delta, Alaska

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