The author of this paper -- was my "undergraduate science godfather" in 1957-61 -- and i accidently found this paper while writing my dissertation nine years later. This is "rocky" - about who you can read in the 'fillossophee' folder -- and the article: 'how did dr. leyden ever become a teacher?'

Skip to the last section ( a final word ) - printed in bold face -- to find the PHILOSOPHY of this teacher. Then -- read the article -- it is filled with arithmetic -- not 'real math' -- simple multiplying -- length x width x etc.

one of the most worthwhile experiences which may be had by HS pupils in connection with the study of erosion is to estimate the rate at which a local creek removes rock material in solution and suspension. This project give the pupils first hand evidence of the rate of erosion in their home area, evidence which is far more meaningful to them than textbook statements concerning some far-off river. It does much toward acquainting them with the methods of science if they themselves plan and carry out the work and then subject their methods and findings to critical analysis. It provides an often-needed review of simple math. Furthermore, it seems to intrigue most pupils to the point where they WANT to do it.

cobleskill creek is a typical small stream in east-central New York. Near the school it is about 70 ft in width and normally average about a foot in depth. It's gradient in this area is between 20-25 ft per mile. The flow is consequently fairly slow, but not sluggish. The water is generally quite clear and becomes appreciably muddy only during times of high water the area drained by the creek and its tributaries about Cobleskill approximates 95 sq. mi. The region is hilly and constitutes a part of what may be considered the northern foothills of the Catskill Mountains. The higher hills attain elevations between 2,000 and 2,500 ft, while the creek at Cobleskill is about 900 ft above sea level ( eiu is about 700 ft ASL ). The greater part of the drainage basin is underlain by shale and sandstone, with some limestone in the headwater region of West Creek and in the lower part of the Coblesikill valley. With the exception of infrequent cliffs and banks, the bed rock is veneered with glacial till and, in the larger valleys, with glacial lake deposits of clay, silt and sand. Near Cobleskill the creek bed consists largely of gravel. Farther upstream, however, the creek and its tributaries flow variously on gravel, sand, silt, clay and their mixtures.

Nearly half of the drainage area consists of crop land. The rest is devoted mainly to pasture, with some woodland on the higher hills.

before he reads farther . . . the reader is invited to estimate the amount of suspenede and solution (solute) carried by the river each day . . and compare the findings to ours.

they paced off a distance of 100ft where the stream was fairly straight and its width depth and velocity fairly uniform, and estimated the average width and depth. They determined the time it took sticks to float 100ft . . and obtain a gallon of water as a sample. later, in class . . the volume of the stream was obtained by multiplying WDV ( width x depth x velocity ) x the number of seconds in a day . and multiplied by a correction factor of 80% . . . to take into account the fact that the bottom water of the stream , due to friction, was not going as fast as the surface water. For the type of stream bottom encountered our references said that the surface velocity of 80% would be a good estimation of the total water velocity.

the sample of water was filtered and then boiled off in a new beaker, previously weights to the 0.01 g. The boiling of the final few ml was done over a water bath. A think brownish deposit of scale remained . . . its weight was determined. Finally the rate of removal of dissolved minerals, in tons per day was calculated: 25 tons. later, in a discussion, the pupils listed possible sources of error in this estimate and suggested ways of making the determination more valid. Considerable time was spent on this phase of the work since it seemed to to one of the most important parts of the entire projects.

the following criticisms were mentioned

• probability
  of considerable error - measuring L / W / D / V of changes in weight of the dissolved minerals caused by chemical changes accompanying the boiling off of the water
• uncertainty
  of the correctness factor 80% as to whether the water sample was truly representative of the water that flowed thru the stream that instant or that day
• possibility
  of error in measuring volume of water sample / wt of residue that suspended material of colloidal dimensions had not been removed by filtration

at this point the instructor mentioned the criticisms above . . so this class were more accurate in their stream measurements . . .

w = 70 ft --- d = 9" --- v = 2 ft / sec --- 7.08 liter sample

0.98 g = wt of solute -- 80% = correction factor
ANSWER: 31 tons

70 ft x .75 ft x 2 ft/sec x 86,400 sec/day x 7.48 gal/cu ft x .8 factor = 54,286,848 gal

7.08 liters had 0.98 grams: so 1 L = 0.1384 g: so 1 GAL (3.785 L) = .524 g

in order to determine roughly the limits of accuracy of this value, the pupils nest estimated, to their best judgment, the probable limits of accuracy of each of the contributing measurements. For example, they decided the values could be high or low by a factor of:

L = +/- 0.5 ft --- w = 68-72 ft; --- velocity 100 ft in 50 sec +/- 5 sec

however, since it is unlikely that the measurements were all too high or all too low, the errors probably offset each other to a considerable extent and the actual value probably lies well within the two limits.

if the estimated 31 tons per day is correct and if it is representative for the entire year, the 11,000 tons / year is carried in solution by Cobleskill Creek. Since this material is contributed by approximately 95 square miles, each square mile, on the average loses nearly 120 tons per year. If the RR that parallels the creek were to carry the annual load of dissolved mineral carried by the creek ... 200 standard coal cars would be required.

Note: as a ruff check, the author found that 40" of annual rain falls on the area and for 95 sq miles is 839 billion cubic ft of rain.

6.27 x 10 to the 12th gallons
419 to 545 billion = hi and low

another source said 50% to 65% of precipitation is carried off by stream and the rest is lost by evaporation ..

so given these limits ... 4.4 x 10 and 5.7 x l09 cu ft

our estimate for these two years said an average value of 1.4 to 2.7 x l0 to the 9 cu ft respecitvely. Both estimates are too low, a fact that is to be expected cuz of the low water level in the stream at the time ---- 19 to 24,000 tons per year

the rate of flow -- 37,000 cu ft per day -- a 23.3 Liter (?) sample was collected near the surface of the stream ... filtered thru two thickness of filter paper ... then filtrate was perfectly clear ... and the paper had filtered a fine brownish mud with no particles larger than silt size. The weight of the sediment was found to be 0.69 g ... and this material was ignited to remove organic matter and the ash weighted. When the two identical sheets of filter paper were ignited to compare that ash ... the weight of the sediment after ignition was found to be 0.58 g.

Note: This would be about 25 ppm; resources say sediment would be 16 to 26 ppm.

ignition of the sediment, beside removing the organic material, undoubtedly caused the partial decomposition of some minerals, especially carbonates, and oxidation of others with a consequent change in weigh ... altho probably not very great. Future classes could make it a point to determine the extent of this error. ... and substitute a better method.

the rate of removal of rock material ... was nearly 29 tons per day. Probable limits of 47 and 18 tons per day were determined by the pupils, while using the "square root of the sum of the squares" method g ave limits of 37 and 21 tons per day.

since the rate of discharge of the creek on the day the data was obtained was considerably higher than average, and since the little inorganic sediment is carried during low water, this estimate is certainly too high for the year as a while. However, during a total of about two months of the year the creek is generally about as high as when the measurements were taken. Furthermore, the water on this day we derived largely from melting snow ( there had been no ppt the previous two weeks ) and as pointed out by Gilbert, run-off from this source caries less suspended sediment than that derived from rains.

with these facts in mind, it seems that our estimate is probably not more than five times as high as the actual average daily rate. If this is the case, more than 2,000 tons of suspended sediment are being carried past Cobleskill each year, and average annual loss of about 22 tons for each square mile of drainage area. This amount does not, of course, include sand grains and pebbles which are undoubtedly transported in large quantities by rolling and saltation along the creek bed.

the writer considers the foregoing project as having been successful in his classes. Some phases of the work have been difficult for the slower pupils, yet not impossibly so, while the brighter have found much to stimulate originality and critical thinking.

possibly one reason for the appeal the project seems to have is that it constitutes, in a small way, original research. The pupils are not concerned with merely 'verifying' someone's law or in arriving at a value as close as possible to that in the book. They seem to take pride in realizing that they are the experts on this particular subject.

the projects have been time-consuming. For even a small class to plan and carry out the field and laboratory work, do the calculations, criticize the method, and discuss the validity and significance of the findings has required five or more hours of class time, in addition to outside work. Moreover, the field work has necessitated the adjustment of schedules and other special arrangements.

the writer considers the value of the project to outweigh by far these difficulties. The time has certainly been well spent. It is true that the pupils could have been told a great many facts in the same time, but this would hardly have resulted in an effective learning as that brought about by the solution of a real problem.

in regard to field work -- any study of earth science that does not include at least some opportunity to observe real things and real processes in their natural settings is not worthy of the name.

the validity of our estimates is, at the least, questionable. To obtain really accurate results would require elaborate equipment and techniques, and a far greater number of observations. These things would defeat our purpose since they would raise the work above the level of the pupils with whom we are dealing. If we give these pupils first-hand contacts with erosion, extend their thinking to include a little of the quantitative aspect of the process, and help them realize the possibility of shortcomings in our methods and those of scientists -- then the work is worthwhile.