LIMNOLOGICAL AND METEOROLOGICAL OBSERVATION TOWERS IN THE GREAT LAKES Roger E. Deane Great Lakes Institute, University of Toronto

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1 LIMNOLOGICAL AND METEOROLOGICAL OBSERVATION TOWERS IN THE GREAT LAKES Roger E. Deane Great Lakes Institute, University of Toronto ABSTRACT Six limnological and mctcorological single-shaft towers of 4-in. pipe were installed in 3 of the Great Lakes by the Great Lakes Institute, University of Toronto. The towers were of two types, a shallow-water tower for depths of less than 60 ft where the base of the tower rcstcd directly on the lake bottom, and a deep-water tower supported by a buoyancy tank 25 ft below lake level. A platform on the towers, situated 8 to 12 ft above lake level, gave a stable base to house limnological and meteorological instruments and recorders. The platform and upper part of tower were designed for easy removal and reinstallation. INTRODUCTION Lake currents and related phenomena in biology, physics, and chemistry are, to a Limnological and meteorological data large extent, caused by and modified by the have been collected from various parts of meteorological environment. Therefore limthe Great Lakes for several decades. Fixed nological data cannot bc appraised properly stations, such as water intake plants, have maintained a variety of records, including without associated meteorological information. In addition, the gathering of data temperature, pi1, dissolved oxygen, conductivity, chlorides, bacteria, etc., over the in both meteorology and limnology at an years. Floating stations, such as the various isolated station on a lake is of little assistresearch vessels, are now collecting meteorance in studying the current pattern of the lological and limnological information, some lake as a whole. Observations must be on a year-round basis. Meteorological obscrmade continuously and at a number of vations are made at various establishments localities if the changes that are constantly around the Lakes and, to a limited extent, taking place are to bc measured and asiby ships. sesscd. The completeness of the overall picture will vary directly with the number and The above data are indespensable in that distribution of observations. A practical they help to fill in the information blanks method of obtaining this information is to in our knowledge of the lakes, All of them, however, suffer from one or more defiequip a number of observation towers with ciencies. self-recording instruments or instruments From the meteorological vicwpoint, the wind velocities and direction, air capable of transmitting the data to a shore station. temperatures, and other parameters which make up the bulk of data taken, pertain to In the spring of 1961 the Great Lakes land and not water and consequently differ, Institute established 6 meteorological obby varying degrees depending on location, servation towers in three of the Great Lakes. from conditions existing over the water, Two were located in Lake Ontario, one in Limnological data collected at fixed shore Lake Erie, and three in Lake Huron. The stations generally lack related metcorologilocation of these towers is given in Table cal information and, in addition, usually 1. The Institute wishes to acknowlcdgc the refer to information only at one point-the support of the Atomic Energy of Canada intake opening. Research vessels, although Limited, the National Science Foundation, coming closest to relating atmosphere and Washington, D. C., and the City of Hamilhydrosphere phenomena, attempt to col- ton in supplying funds to cover the cost of lect data from different levels in both air the towers. Tribute must also be paid to an d water but cannot be everywhere at the cndurancc and patience of the crew once and so fail to show changing condi- of C.C.G.S. Porte Llauphine during the tions at any one location, many trials and tribulations associated 9

2 10 ROGER E. DEANE Lake Ontario Ontario Erie TABLE 1. Details of the observation towers -. ~ -.-.~..-- Nearest port co-m&nclrtes Type of tower ~ IIamilton Burlington Port Burwell Huron Douglas Point Huron Douglas Point Huron Douglas Point --- Lat. 43O16.1 N Shallow Long W Lat N Long. 79O45.5 W Shallow Lat. 42O35.8 N Shallow T,ong. 8OT2.0 W Lat. 44O19.4 N Long W Lat N Long. 81O38.0 W Lat N Long. 8OO40.0 W shallow Shallow Deep Depth of Distance water from shore Cm) (In) , , ,630 Instrumentation anemometer, 2 water thermistors 2 water thermistors 3 anemometers, 3 air thermistors, rain gauge, 5 water thermistors rain gauge 3 anemometers, 3 air thermistors, rain gauge, 5 water thermistors, 3 current meters anemometer, rain gauge, 2 water thermocouples with tower installation. Without aid of the Department of Transport, Ottawa, this program could not have been undertaken. DESIGN OF OBSERVATION TOWERS Basic principles Certain basic principles governed the design of the towers. The first consideration was to make them inexpensive to construct because they were essentially experimental in design but, if successful, would eventually be required in large numbers. Secondly, the towers must offer the least possible resistance to wind and waves. ( Currents were not considered as important factors in affecting the stability of the towers.) Thirdly, they must be adaptable to all depths of water. Fourthly, because of winter icing conditions, that part of the tower projecting above.water must be constructed so as to be easily removed and replaced. Two types of towers were constructed; a shallow-water type for depths of less than 60 ft, and a deep-water type for depths greater than 60 ft. The main difference between these two kinds was that the shallowwater tower rested directly on the lake bottom, whereas the deep-water tower was supported by a buoyancy tank. Shallow-water tower A diagrammatic sketch of this tower is shown in Figure 1. The tower shaft was made of standard 4-in. black water pipe. This pipe, of %-in. steel, can be obtained from stock in 2O-ft lengths which can be threaded and joined with standard flanges. The base of the shaft consisted of 4 pieces of 3X-in. by 5-in. angle iron, each 10 ft long, welded to the bottom of the pipe in the form of a cross. Supporting members of 2in. angle iron connected the ends of the base to the pipe of the tower. The length

3 OBSERVATION TOWERS IN THE GREAT LAKES /E Aluminum Most - 25 High LAKE ~~ ~,=--.e , Standard Pipe - Angle Iron Support - Angle Iron Bose - 3-i/Z x$ r IO B lb Concrete Guy Anchor FIG. 1. Diagrammatic sketch of shallow-water limnological and meteorological observation tower. of pipe in each tower varied with the depth of water at the desired location. If the lake bottom consisted of soft sediments the tower pipe projected 2 or 3 ft beyond the bsase for penetration into the sediment in order to give added stability to the tower. If the lake bottom was composed of till or bedrock the tower pipe was flush with the angle iron base. For stability the tower was guyed with %-in, cable to 3 or more concrete guy anchors each weighing approximately 3,000 lb. The guy cables were fastened to the tower pipe just below the upper flange, or a,pproximately 10 ft below lake level. The anchors were equally spaced around the base of the shaft and positioned so that the guy cables made angles of approximately 45 with the tower. The towers extended from 7 to 12 ft above calm lake level. A platform, generally of %-in. plywood, 4 ft by 4 ft, was bolted to a flange which was welded to the top of each tower. Four supports of l-in. standard pipe connected the corners of the platform to the tower. These supports were approximately 3% ft long and made an angle of about 45 with the tower pipe. A mast for meteorological instruments projected above the platform ( see Fig. 2).

4 12 ROGER E. DEANE c -- METEOROLOGICAL MAST 2-3/8 OD EXTENDING 25 ABOVE PLATFORM FLOOR FLANGE - 45 ELBOW -- -3/4 PLY WOOD PLATFORM l/2 STANDARD PIPE SUPPORT 45 ELBOW - -COLLAR WELDED TO PIPE METEOROLOGICAL MAST EXTENDING 5 INTO TOWER PIPE- a 1 I I I I I - -.p4 ID TOWER PIPE -- - m-4 CIRCULAR DISK FIG. 2. Sketch of mast and platform construction. The mast, of 2%in. O.D. aluminum pipe with %-in. wall, was 30 ft long. The base of the mast was fitted with a 4-in. disk designed to slide into the tower pipe, A 2% in. I.D. collar was fastened to the platform and permitted the mast to slide through it. Five feet of the mast remained in the tower pipe to give support to the 25 ft which projected above the platform. The sliding parts of the mast permitted it to be lowered into the tower pipe, the instruments attached, and the mast raised back into position. Five shallow-water towers were installed; two in each of Lakes Ontario and Huron, and one in Lake Erie. Deep-water tower The mast, platform, and tower shaft of the deep-water tower were identical to those of the shallow-water type. However, whereas the shallow-water tower was supported by the lake floor, the deep-water tower was suspended by a buoyancy tank (see Fig. 3). This tank, approximately 7 ft long by 3 ft in diameter, was constructed of Soin. sheet steel, A 20-ft length of 4-in. tower pipe was inserted through the tank so that about 5 ft projected below. The pipe and tank were welded together and made watertight. A 20-ft length of standard pipe was fastened by normal couplings to each end of

5 OBSERVATION TOWERS IN THE GREAT LAKES 13 7 ~ 3 Diameter Standard 3Ki Anchor Cable I9 FIG. 3. Diagrammatic sketch of deep-water limnological and meteorological observation tower. the tank section. A 5,000-lb concrete anchor nated most of the motion due to surface was attached to the lower end of the tower waves. The tank was designed to give pipe by a y&in. cable of sufficient length to about 1,000 lb buoyancy over and above allow 10 ft of the tower to project above that required to compensate for the weight lake level when the anchor rested on the of the platform, pipe, tank, and cables. lake floor. A deep-water tower was installed in Lake To prevent oscillation and rotation, 3 Huron in 207 ft of water about 3% miles arms of IX-in. pipe, each 4 ft long, were offshore from Douglas Point. welded to the tower pipe 5 ft below the Both types of towers had several features upper flange. Guy cables were fastened to in common. The platform and upper 20 ft the pipe just above these pipe arms, passed of pipe could readily be removed by unthrough them, and attached to 3,000~lb guy screwing the bolts of the upper flange. anchors located at positions so that the This was important because ice conditions cable joined the pipe at angles of 45. in the Great Lakes in winter necessitate The location of the buoyancy tank at the removal of the platforms and meteora.pproximately 25 ft below lake level elimi- ological equipment. In addition, the anchor

6 14 ROGER E. DEANE guys in both types were fastened to the upper flange to enable removal of the platforms without disturbing the remainder of the tower. Also, the absence of guys above the lake level lessened the hazards of collision by boats. INSTALLATION OF TOWERS The towers were installed from the Porte Dauphine. For the shallow-water type the guy anchors were put in position first and the free ends of the guy cables attached to floats to mark the anchor locations. The ship was then positioned in the middle of the floats ready for the installation of the tower. The three 20-ft sections, beginning with the base of the tower, were lowered over the side of the vessel and joined together by flanges until the complete tower was assembled. The anchor guys were then temporarily attached to the tower platform and the ship removed from the immediate vicinity. Scuba divers completed the installation by attaching the guy cables to the tower pipe. The installation of the deep-water tower proved to be easier than the other type. The three 20-ft sections, assembled on the water alongside the ship, floated horizontally because of the buoyancy tank. The 5,000-lb anchor was then swung over the side of the ship by block and tackle and sufficient anchor cable attached between it and the basal end of the tower pipe to allow approximately 10 ft of the platform end to project above lake level when placed in position. The anchor was then lowered to the lake bottom, the guy anchors positioned, and the guy cables attached to the tower. INSTRWMENTATION The towers were designed for instrumentation according to the plan set out in Table 1. Limnological and mleteorological equipment was installed on the platforms after the towers were placed in position. Meteorological masts, projecting 25 ft above the platform were erected on two of the towers. An anemometer and thermistor were positioned at the top, at approximately mid-point, and near the base of each mast, thus giving wind velocity, wind direction, and air temperature at approximately 35 ft, 24 ft, and 12 ft above lake level. The lower mid-position instruments were attached to l-in. diameter cross arms 5 ft out from the mast. Rain gauges attached to the platform completed the meteorological instruments, Single anemometers were fixed directly to the platforms on the other four towers. The towers were designed to support current meters suspended at different levels and thermistors attached at IO-Et intervals between lake surface and bottom. The recording of data from both meteorological and limnological instruments was designed to be automatic. At the shallowwater tower located 2,600 ft offshore at Douglas Point a 32conductor cable 3,500 ft in length connected the instruments on the tower to a recorder located on shore. Such a method is not suitable for towers situated much over a mile from shore but, where feasible, it has advantages over other methods. A second method of recording data consisted of installing both the recorder and battery power on the tower platform. This method was used on the other 5 towers installed in The recorders required servicing once a week-an obvious disadvantage to this method, but one which could bc overcome by using long-term recorders. The tower platform off Port Burwell supported approximately 1,000 lb of battery as well as a recorder and meteorological instruments. This weight would be a distinct disadvantage on the deep-water towers. However, two additional methods which could bc used are: a floating tender located in close proximity to the tower housing the recorder and battery power, or an underwater housing attached to the tower containing the power supply and recording instruments. CONCLUSIONS Some modifications to the original design and concept of the towers were found

7 OBSERVATION TOWERS IN THE GREAT LAKES 15 necessary following installation and use of the towers through the summer of The desired spacing of 120 between guy anchors was difficult to achieve. Because of this 4 to 6 anchors arc to bc preferred, particularly where the lake bottom is smooth rock. Additional guy supports are also necessary for the meteorological mast to prevent movement in strong winds. The cast iron flanges joining the individual pipes were the main weakness in the 1961 towers. These should be replaced by sleeves or steel flanges in future towers. In addition the platforms should be at least 15 ft above the mean lake level in bodies of water the size of the Great Lakes. The platforms of the two shallow-water towers off Douglass Point, rising 11 ft and 12 ft respectively above lake level, were covered by storm waves on two occasions. The cost of material for each tower was less than $

Irrigation &Hydraulics Department lb / ft to kg/lit.

CAIRO UNIVERSITY FLUID MECHANICS Faculty of Engineering nd Year CIVIL ENG. Irrigation &Hydraulics Department 010-011 1. FLUID PROPERTIES 1. Identify the dimensions and units for the following engineering