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Historically: How to Site a Mill

Henry Ford Grist Mill at the Wayside Inn, Sudbury, Massachusetts
New mill construction in 1926
by the Fitz Water Wheel Company, Hanover, Pennsylvania

Historically: How to Site a Mill
Theodore R. Hazen

MILL SITE. A mill seat is a suitable place for a water mill. A mill site is the mill seat and the above mill dam. The mill dam is an interruption in the flow of water, raises and maintains the water flow so as to make it available to turn a water wheel.

WATER POWER SYSTEMS. Three functions of a water power system is to deliver large amounts of water to a water wheel, remove the energy from the water through the action of the water wheel, and disposing of the used water or returning it to the stream below the mill.

Illustration from:Mills on the Tsatsawassa:
Techniques for Documenting Early 19th Century Water-Power Industry in Rural New York,
by Philip L. Lord, Purple Mountain Press, Fleischmanns, New York, 1983.

Water power systems consist of a number of elements. The "DAM" serves two purposes: first, to raise the water; second, it creates an impoundment or reservoir which acts as an energy bank. Water flows the same day and night, so it is saved during the night to be used the next day. In "SPILL WAYS", gates are used to raise or lower the water level and flow. Some are built to hold planks called "FLASH BOARDS" which can be put on or taken off to regulate the water level of the pond or reservoir. They are removed at times of freshets or flood stages. The "RACE" has two types, "HEAD," and "TAIL" RACE. The race carries the water from the dam to the mill site. A race may be from a few feet to miles in length depending on the distance between the dam and the mill site. The same race may serve one mill or many mills. At the mouth of the race there is often a "TRASH RACK," which stops floating logs and large debris from damaging the water wheel. Behind the trash rack and at the end of the race are "GATES." The gates allow the mill operator to control how much water is in the race and enters the water wheel. These two types of gates are called "HEAD GATE" and "SLUICE GATE" (or "CONTROL GATE.") A "FLUME," "SLUICE" or "PEN STOCK" carries the water at an elevated level above ground to the water wheel. Flumes are either open or closed, while a pen stock is in the form of water tight pipe. Pen stocks are either cast iron pipe, sheet iron pipe, concrete pipe, or the traditional wooden pipe. Later mills had dams with water being led to the wheel by a short race or flume. After the water flows through the water wheel it is then returned to the stream below the mill. It flows through a "TAIL RACE."

Undershot Water Wheel & "High" Breast Shot Water Wheel

A water wheel or turbine must have the used water removed from the wheel so sufficient fall is given to the tail race to quickly carry the water away from the water wheel, while the head race maintains the height and level of the water from the dam to the wheel. There are two basic types of water motors, "VERTICAL WATER WHEELS" and "HORIZONTAL WATER WHEELS." The three common types of vertical water wheels are the "UNDERSHOT," the "BREAST," and the "OVERSHOT." The two common horizontal water wheels are the "TUB WATER WHEEL," and the "TURBINE WATER WHEEL."

The two basic principles which operate on all water wheels is "IMPACT" (or "FLOW"), and "FALL." The difference in elevation between the water level in the mill pond and where it leaves the water wheel is called the "HEAD." The end of the flume is called the "WATER BOX." This is where the control gate is.

The general rule is that if the difference between the top of the dam and the water surface at the tail race is less than 6 feet, and the water could only flow under the wheel, you would use an undershot water wheel, or horizontal water wheel. If the difference is less than 10 feet and a flume or sluice is able to carry water to the top of the wheel, but the water would be high enough to fill up some of the wheel's buckets, you use a breast water wheel. If the difference is greater than 10 feet and the water would be high enough to fill up the wheel's buckets at the top of the water wheel, you use an overshot water wheel. Breast water wheels are more efficient than undershot water wheels, but the overshot water wheels are the most efficient.

Until the late 1700's millwrights thought the undershot was the most efficient type of water wheel because the rushing and bubbling water looked powerful. In Europe the most common type of water wheel was often the undershot, because of its additional use in tidal and boat mills. The undershot was the basic water wheel all millwrights learned to construct. Some millwrights in Europe only learned to construct undershot water wheels so when they came to America they might construct an undershot water wheel operating from a 40 foot fall. The development of the "ELBOW BUCKET" was a great advancement over the "FLAT PADDLE" open bucket or "FLOAT," primarily used on the undershot water wheels.

In the United Kingdom and Europe the undershot, breast shot, and pitch back water wheels were classified as undershot because the water flowed under these types of water wheels. There are two types of traditional undershot water wheels, the undershot and the flutter wheel. There are three types of traditional breast shot water wheels, the low breast, middle breast and high breast water wheels. There are two types of traditional overshot water wheels, the overshot and the pitch back water wheels.

Middle Breast Shot Water Wheel
"The Young Mill-Wright and Miller's Guide,"
by Oliver Evans

In the early 1800's the most common water wheel used to power American industry was the breast water wheel. It was not until the 1840's did millwrights discover which type of water wheel was the most efficient in different places according to the available head, not the available flow. Wooden water wheels had several drawbacks: they rotted out every ten to twenty years, and they could not be operated in cases of ice, imbalance and debris. From the 1820's to 1840's water wheels began to be constructed with cast iron shafts and hubs. In the 1870's all steel water wheels eliminated the problems with imbalance, rot, ice and debris.

Water power systems have both disadvantages and advantages. The advantages are many. They use energy that is free, they do not pollute, they do not use up the energy source, they return it to the stream unchanged, and they add oxygen to the water which helps aquatic life. However, a disadvantage is that they are effected by droughts, and floods. At one time there were thousands of small water powered mills in use. As a general rule water powered mills from northern Virginia north into Maryland, Pennsylvania, New Jersey, New York, and New England, often had their water wheels inside of the mill building to protect them from ice and freezing. Mills south of northern Virginia usually had their water wheels outside of the mill structure. Historically some water mills constructed a roof or awning over the water wheels to protect the wheels. These roofed covered wheels might be either wide overshot, breast shot or undershot water wheels. When a traditional wooden water wheel (which was enclosed within the mill) was replaced by the modern Fitz Water Wheel they too occupied the same original space as the old wheels.


The improvements seen in Oliver Evans' Automated Mill were developed from 1782-83. The first edition of Evans work was published in "The Young Mill-Wright and Miller's Guide," in 1795. Most mills constructed until the 1870's were probably similar to the internal workings of an Oliver Evans Mill. Most mills prior to Oliver Evans involved much manual labor in the moving of grain and flour within the mill building. Many mills were clustered along tiny mill streams. Before Oliver Evans, many industrial complexes remained small and sometimes very isolated. With the improvements of Oliver Evans, mill centers developed in areas either near the supply of grains or close to the markets or sea ports. At the beginning of the American Civil War, Richmond was the largest flour milling center in America. Wheat grown in Virginia was superior to that grown in other areas for bread baking. Besides Richmond, Virginia, and the Shenandoah and Cumberland Valleys, other regions also had Oliver Evans influenced mills in the late 1700's and early 1800's; such as in the Brandywine Valley north of Wilmington, and in the Baltimore area. Virginia, Maryland, and Delaware led the way with America's first installation of automated mill systems.

For the millwrights to harness the power of water to operate a mill, they had to consider several elements. The mill stream had to have a fairly dependable flow of water, and with sufficient fall to turn a water wheel without creating the necessity for erecting huge dams. The stream had to provide a natural dam site for the stability of the dam once built. Broad valley floors provide poor sites for damming, whereas valleys with a natural constriction not only limit the necessary size of the dam but provide more effective anchoring points for the structure. A good mill pond location immediately upstream of the mill dam must provide for the impoundment of enough water to operate the machinery even during periods of relative drought. In areas were the incline of the stream bed and where the ponds are confined between steep banks,
they could not hold much water unless the dam was quite high. An area above a natural constriction would be ideal to create a mill pond. Lower dams were better for construction and repair costs, besides the dam structure would have considerably less risk of undue water pressure, ice jams, and flooding problems.

Mill ponds situated in narrow valleys must be backed up a considerable distance in order to impound sufficient water for the daily mill operation. The slope of the valley floor ideally should not be raised high above the dam site. A valley floor whose slope raises high above the top of the dam will require an equally high dam structure. The terrain should open up just above the dam site. When the pond is filled with water, it should be at a moderate elevation. Mill ponds situated in broad valleys could impound sufficient water within a very short distance above the dam, thus reducing the area and height of the mill dam.

Dams which are built of wood are anchored against wood and stone abutments to the creek banks. These abutments provide greater stability for the dam structure and tend to prevent erosion and the undermining of the dam caused by high water running around the abutments. Dams built of log or timber cribbing are filled with stone rubble and faced on the upstream side with fitted boards to resist leakage. Wood dams are not as durable as stone dams, but are very strong and are more easily rebuilt if the dam is destroyed by spring floods.

At least two outlets are required for each dam. The first is the spill way which allows the surplus water to flow past and over the dam once the pond is full. The second is where the water will flow to the mill via a mill race, flume, or sluice. This second outlet can be a simple ditch, often lined with stone or wood, or may be a complex wooden stave flume or plank box sluice. A third outlet would be a natural overflow or seepage for the rising spring floods, often away from the area of the milling complexes.


The miller who operated the mill and the millwright who constructed the mill were each masters of milling. A miller was expert with his controlling devices: the wheels, shafts gear trains, and the knowledge of how to adjust his massive millstones to less than a wheat grains thickness apart. Well-balanced millstones can be a paper's thickness apart. The millwright through the apprentice system (prior to Oliver Evans' book) learned the advanced technical knowledge necessary to milling more so then anyone in the colonies. The millwright knew how to find natural ravines where dams could be built to feed water to a mill as much as a mile away and maintain the height of the water to the top of a water wheel. The millwright could lay out mill races or canals at a constant elevation, following the natural contours of the hillsides to bring the water to the mill at a point downstream where the water would fall or drop on the wheel. The dropping point was a "FALL" in millwright terminology. The water had to not only fall over or upon the water wheel, but it also had to drain away downstream as efficiently as possible. The millwright had to ensure that the water did not form a sluggish puddle under the wheel to slow its rotation and diminish its power. The mystery once solved allowed successful placement of a mill where none was ever known to exist. Millwrights would use all of the knowledge to make eventual solutions so that a system of shafts and gears would be used to transmit power from the water wheel to one or more sets of millstones. As the water wheel turned, the main shaft would be mounted to run the millstones as well as to power additional machines of the mill by means of a system of belts and pulleys.

Oliver Evans' book "The Young Mill-Wright and Miller's Guide" also solved the great hydrostatic paradox of the time. The hydraulics problem was to determine which water wheel to use, the overshot, the pitch back, the breast shot, or the under shot. And then once the water wheel type was determined, it was critical to judge which size of millstones was appropriate for the water wheel chosen. This knowledge prior to Evans was only accessible to the master millwright. Many early colonists built both tub mills and vertical mills. A "TUB MILL" was the most primitive type of mill, with its water wheel inside the building itself. The wheel was mounted on the same shaft as the turning runner millstone. The wheel was placed in a tub to cut down on the waste of water. Since the wheel is set parallel to the ground, a tub mill was classified as a "HORIZONTAL MILL." The water was funneled through a flume to the blades on the water wheel and the sheer force of the moving water made the wheel turn. The main shaft and the runner millstone mounted on it turned at the same speed as the water wheel. This unsophisticated system was also called a "GREEK MILL," "NORSE MILL" or "SWEDE'S MILL." This type of mill could be easily transported to a better site if the water power proved inadequate. A typical tub mill structure measured about 12 by 14 feet. The familiar "VERTICAL MILL" has its water wheel mounted on the side of the mill building perpendicular to the earth, with the axle mounted horizontally. The vertical mill wheel made it necessary to build a gear system to change the horizontal rotation of the main shaft into a vertical motion that could be used inside the mill to power the millstones. The smallest and the largest vertical mills have a gear system, incorporating wooden (squirrel cage) pinion gears (called "TRUNDLES") that were mounted at the bottom of the shafts that turned the runner millstone. The colonial millwright could plan a mill that would not only turn corners with motive power, but also make the millstones revolve at a rate faster than the slow but steady turning water wheel. When Oliver Evans patented his improvements in 1787 they increased the efficiency and cost effectiveness of mills. Oliver Evans published his book on mill construction and operation in 1795. This handy guide for putting up mills may account for the underlying similarity among 19th century mills that on the exterior look very different. Many millwrights simply would copy the cross-section drawings of the layout of Oliver Evans' machinery directly from his book.

Mills in America passed through at least four major eras of technology:

1. The traditional pre-settlement European technology ("LOW MILLING," "FLAT MILLING," or "AMERICAN MILLING" technology).
2. The Oliver Evans "AUTOMATED MILLING SYSTEM" of 1787.
3. The NEW PROCESS MILLING SYSTEM of the 1850's and 1860's ("HALF-HIGH MILLING" technology) which involves regrinding middlings on smaller diameter millstones.
4. The Roller Mill system of the 1870's ("HIGH GRINDING," or "GRADUAL REDUCTION" technology), which incorporated the New Process milling system and the use of the "ROLLER PROCESS." This process of "WHEAT SAW MILLING" was developed by Hungarian engineers in the mid-century.

There is a close connection between the agricultural hinterland and the flour hungry seaports such as New York, Wilmington, Baltimore, and Richmond. The Napoleonic wars ran the price of American flour prices up per barrel, and even after the war. The larger mills were called "MERCHANT MILLS" whose owners were capitalists with large investments. They bought wheat and manufactured it into flour for retail sale to the neighborhood and bulk sales by barrel to brokers. The "CUSTOM MILLS" or "COUNTRY MILLS," on the other hand, were the small operations where the miller ground grain for customers and kept a fraction of the output as his fee or "TOLL," rather than charging in cash for grinding. Some country mills made no fine flour at all, just grinding corn, buckwheat, rye, oats, and animal feeds. After the 1920's, larger mills' flour production began the end of the era of small rural Virginia mills. Buildings began to either decay or were put to other uses. The western wheat and flour milling centers (such as in Minneapolis) began to win over the ancient eastern milling industry. Virginia mills operated on a local trade and on feed production. The packaged western flour shipped by rail undersold that made by local Virginia millstone and roller mills milling wheat grown often within sight of these Virginia mills. A pattern of bankruptcies and trustee's sales developed, with mills selling at lower prices at each successive auction and many of the mills being stripped of the machinery which was moved elsewhere.


Some of the terminology of flour milling may be perplexing to the modern reader. For example, the mill building itself was long referred to as "THE MILL HOUSE," but later "THE MILL HOUSE" came to mean the "MILLER'S HOUSE," or dwelling rather than the functioning mill. "A SET OF MILLS" often meant merely one mill building, possibly equipped with more than one set of grinding mechanisms, often meaning equipped with a saw mill besides a grinding operation. "A DOUBLE MILL" was referred to in the plural although only one mill structure occupied that particular site. A double mill may mean two water wheels operating two separate sets of gearing and millstones, or a double mill may also mean a mill which includes two separate milling operations such as grinding and sawing mills in the same structure. In describing the mill's machinery or equipment of a mill, a "RUN OF STONES" meant one complete set of grinding stones, the upper "RUNNER" stone and the lower "BED" stone. A "TWO RUN OF STONES" indicated two complete and separate units in the same mill, four millstones in two pairs. The "RUN" of the mill is what the mill grinds or the amount of grain ground by the millstones in a given period. A "RUN" is another name for a "PAIR" of millstones. A "MILL RUN" is another name for the "HEAD RACE" and also "MILL RUN" refers to what the mill was grinding each day. There is the "HEAD" or fall of water and the "head" of the barrel which the miller places his flour. To run the millstones too "THIN" means to run the stones with too little feed which could ruin the millstones. A "MILL BILL" is not a statement of charges or a list of items but another name for a "MILL PICK" which is used to "DRESS" or sharpen the millstones. Going "THROUGH THE MILL" does not mean touring the mill structure but the grain that has traveled "THROUGH THE MILLSTONES."

An overshot water wheel.

This water wheel suffers from the most common problem with wooden water wheels. The water enters the buckets forward of the vertical center of the water wheel. The water should leave the end of the chute behind the vertical center so the water wheel gets full benefit of the fall of the water. In may water wheels that the water enters the buckets in front of the vertical center much of the water can fly over or overshoot the wheel and be wasted. See: Fitz Steel Overshoot Water Wheels, Bulletin No. 70, Decmeber 1928, by the Fitz Water Wheel Company, Comparison With Wood Wheels

Typical Mill Site, Robert Howard and Thomas Sweeny III.
From "Waterpower, How It Works," by Robert A. Howard,
Eleutherian Mills Hagley Foundation, Inc., Greenville, Delaware, 1979.


1. Selection of a mill seat or privilege. Does the stream site have an abrupt descent on the stream bed, a succession of lesser falls, or an extended rapids offering a concentration of fall favorable to power development.

2. The greater the height of the fall, the less the volume of water required to obtain a given amount of power, thus reducing the size and expense of the hydraulic facilities from the millpond and tail race.

3. Mill sites are more numerous and sharply defined in hilly terrain and in the upper portions of a river system than in lower valleys with gentler slopes and a typically sedentary character.

4. Typical mill installation consists of a water wheel erected besides or beneath a mill structure; a dam at some suitable point up stream to divert more or less of the flow into the headrace; and to increase the amount of fall (usually to create a pond for storage of the nighttime stream flow); a canal called a millrace, or headrace, to carry the water to the mill with minimal loss of fall; a pen stock, or sluice, with gate, to convey the water to the wheel; and a tail race to carry the water discharged from the wheel with energy largely spent, back to the stream below the mill. A typical mill race and sluice box has 1" to 0" fall.

5. Further appurtenances are needed such as gates to regulate water flow, waste ways for contingencies of flood and high water, and trash racks to keep floating debris and ice from clogging pen stocks and water wheel.

6. Dams are a barrier constructed of locally available material, such as stone, timber, brush and soil, in various arrangements erected across the stream with its ends well anchored in the stream banks on either side. Dams may be a low structure. They are intended to divert water into a head race to maintain the fall and develop horse power.

7. Dams raise the water level and backs water up stream depending upon the height of the dam structure and the character of the local terrain. They create a storage reservoir known as a millpond. This accumulated water will run the mill for hours.

8. The simplest type of mill dam is a crude obstruction of tree trunks, branches, and stones, the openings chinked with gravel, sand, clay, or loam.

9. Timber dams were the most common. A timber crib is filled with stones and rock.

10. Crib dams use narrow channels and high banks on each side. The dam consists of two cribs secured to the natural embankment made of material that the water will not penetrate. The two cribs have a V shaped connection between them with an apron extending 3 or 4 feet forward of the cribs. The V shape and the two cribs form an arch which holds the pressure of the water

11. Masonry Dams were never as common in America as they were in England.

12. Earthen dams generally have a stone or covered spill way.

13. Abutments at the stream banks and tumbling aprons of timber dams are covered with planks or rocks to prevent the water passing over the dam from undermining the dams foundations.

14. The dam should not be too close to the mill. A breach or leak on the fore bay may wash away the mill. The mill should be placed to protect it from floods and high water.

15. Waste water should be free to pass by the mill and not injure it.

16. Wide low dams handle high water or flooding best. Streams with narrow dams during periods of high water or floods will overflow its banks.

17. The dams should have a good foundation. Mill walls should have a separate foundation from the foundation which holds the husk or Hurst frame. It they rest on a common foundation the machinery vibrations will shake down the building around it.

18. Historic Note. The 19th century parcels tend to be internal subdivisions of larger 18th century parcels, such as major lots or military land grants. These larger parcels tend to have been surveyed. Therefore, reconstructing these larger 18th century units can often allow one to accurately locate and correctly position the smaller, otherwise ambiguous, later subdivisions. Since mill dams were often built at the edges of parcels, where those edges intersected the mill stream, the reconstruction of 19th century property lines that may no longer exist can be critical in discovering unmapped dam and pond locations. Hypothetical site plans and hypothetical delivery system suggest and underscore the hypothesis that industrial parcels frequently begin at mill dam locations and that reconstructing parcel intersections with mill streams may often locate previously unmapped dams and ponds of earlier mill sites.

19. Stone should be part of the abutment material in order to establish a stable anchoring point for a mill dam, particularly critical at the sharp bends in the creek or stream and at steep banks.

20. The site should be accessible to the supply of grain, transportation (can you build a road to the mill), and flour markets.


The following is a list of items to consider and identify when establishing a new mill site.


1. Size of mill structure.
2. Number of millstones (types of millstones for different types of flours).
3. Roller mills.
4. Combination millstones and roller mills.
5. Horse power requirements of machinery in the mill (what is the grindings surface of the millstones).


1. Animal and human.
2. Wind.
3. Water: stream and tidal.
4. Steam.
5. Electricity.
6. Diesel.
7. Gas: liquid and natural.

Water Wheel or water motors

1. Type of water wheel: a) horizontal: norse mill, tub wheel, turbine; b) vertical: undershot, flutter, low breast, mid breast, high breast, pitch back, overshot
2. Width of water wheel (if the water wheel is vertical).


1. Types of dams: log, timber, crib, earthen, stone or masonry.
2. Size the area which the dam back floods.
3. Spill way, overflow.
4. Wash out gate.


1. Head race: a) in ground mill races- earthen, earthen lined with stone, wood or brick; b) elevated or buried channels; c) wooden sluice box; d) pen stock, either round wooden pipe, concrete pipe, round masonry stone or brick, or metal pipe of either sheet metal or cast iron pipe.
2. Tail race: open earthen race or enclosed underground race.


1. Trash racks.
2. Head gates.
3. Control gates.
4. Flood gates.

Type of milling operations

1. Custom mill.
2. Merchant mill.
3. Feed Mill.
4. Combination mill.


POWER= Cubic feet per minute x 62.125 (weight per cubic foot of water) x Head (fall)
and divide by 33,000 pounds

Head would equal the 16 foot diameter water wheel plus one foot below the water wheel for the water to flow into the tail race, one foot of water above the water wheel for the water to enter the water wheel, and three feet of water standing in the sluice box. This would equal 21 feet of needed head.

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Copyright 1996 by T. R. Hazen