The Sewerage of Sea Coast Towns Informative Summary

Overview:

The Sewerage of Sea Coast Towns by Henry C. Adams, published in 1905, is a comprehensive guide for engineers tasked with designing sewage systems for coastal towns. It delves into the complexities of tidal forces, explaining their origin and how they influence the movement of water along shorelines. Adams emphasizes the importance of understanding these forces when determining the ideal site for a sea outfall, the point where sewage is discharged into the sea.

The book guides engineers through the process of selecting the outfall location, taking careful consideration of tidal conditions, current patterns, and the presence of sensitive areas like bathing grounds and oyster beds. Adams also examines various methods for gauging sewage flow, the impact of rainfall on sewer capacity, and different approaches to storm overflow design. He further explores the challenges of constructing sea outfalls, including the use of different materials like cast iron and steel pipes, and the importance of diving inspections to ensure structural integrity.

Key Findings:

Tidal forces significantly impact sewage disposal in coastal areas. Understanding the tides and currents is crucial for selecting an outfall site that effectively carries sewage away from the shoreline.
The specific gravity of seawater must be factored into calculations for outfall discharge. This difference in density requires adjusting the effective head used in calculations.
The action of seawater on cement can cause deterioration of concrete structures. Understanding the chemical processes involved and using proper concrete mixes is essential for building durable coastal infrastructure.
Windmills can be a cost-effective solution for pumping sewage in small coastal towns. While windmills offer a sustainable option for pumping, a backup engine is necessary for periods of calm wind.

Learning:

Readers will learn about the forces that create tides and currents. Adams explains the influence of the moon and sun’s gravitational pull, the earth’s rotation, and the geometry of coastlines on tidal patterns.
The importance of current observations in sewage disposal is emphasized. Readers will understand how to collect and interpret data on current direction and velocity to ensure efficient sewage dispersal.
Designing sea outfalls requires careful consideration of tidal conditions and the impact of seawater. The book delves into the specific challenges of building robust outfall structures that withstand the forces of the sea.
Concrete durability in marine environments is a critical factor in outfall construction. Readers will learn about the chemical reactions that can damage concrete and how to mitigate these risks.

Historical Context:

The book was published in 1905, a period of significant growth in urban areas and improvements in public sanitation. This era saw the increasing use of water-closets and the development of sewer systems to improve public health. While sewage disposal was still a relatively new field, the book reflects the growing understanding of its importance in preventing disease and promoting public well-being.

Facts:

The tidal day averages 24 hours and 52 minutes, as the moon moves eastward in its orbit around the earth.
Spring tides occur when the sun and moon are aligned, resulting in higher tides than neap tides.
Neap tides occur when the sun and moon are at right angles to each other, resulting in lower tides than spring tides.
The greatest tide ever recorded in the UK occurred in Chepstow in 1883, with a rise of 48 feet 6 inches.
High water of spring tides occurs at midday on the Greenwich meridian and at midnight on the 180° meridian.
The average rise of spring tides around the coast of England is about 15 feet, while the average rise at neap tides is 11 feet 6 inches.
The mean level of the sea around the coast of England is 0.623 feet above Ordnance datum.
The speed of the primary tidal wave in the Southern Ocean is 543 miles per hour.
The specific gravity of sea water is 1.027, meaning a column of sea water 12 inches high requires a column of fresh water 12 1/3 inches high to balance it.
The action of seawater on cement is primarily due to the reaction of the sulphuric acid in seawater with the calcium hydrate in the cement.
Trass, a finely-ground silica, can improve the resistance of concrete to seawater, particularly when used with weak cement mixes.
A diving dress and equipment weighs about 175 pounds, including lead weights.
The pressure of the water on a diver increases by about 1/2lb per square inch for every foot in depth.
A diver needs about 1.5 cubic feet of air per minute for respiration.
Nitrogen gas from the air is absorbed by the blood and tissues of a diver under pressure.
Decompression after diving is necessary to avoid the formation of nitrogen bubbles in the blood, which can cause divers’ palsy or death.

Statistics:

The average amount of water used per head per day for domestic purposes only is 15 gallons.
The quantity of domestic sewage can vary from 7 to 15 gallons per head per day, depending on the sanitary conveniences installed.
An allowance of 10 gallons per head per day for resident visitors and 5 gallons per head per day for daily trippers is typically sufficient.
The maximum flow of storm water in sewers is directly proportional to the impermeable area and the intensity of rainfall during the time of concentration.
The intensity of rainfall decreases as the period over which it is measured increases.
The average percentage of effective impermeable area in a town is 5 percent, based on a density of 4.9 people per acre.
On the average, only 70 to 80 percent of the rain falling on impermeable areas reaches the sewers.
The cost of constructing a separate surface water system can be approximately 15s. 0d. per lineal yard of road.
The extra cost of pumping storm water can be around 1-1/2 d. per 1,000 gallons.
A 15-mile-per-hour wind is typically available for eight hours per day on average.
A 20-foot diameter windmill is the largest that should be used for pumping sewage, as larger mills are less efficient.
The efficiency of windmills decreases with the size of the wheel, with 8ft, 10ft, and 12ft mills being the most efficient sizes.
About 22 percent of the total daily dry weather flow of sewage is delivered between 7 p.m. and 7 a.m.

Terms:

Aphelion: The point in a planet’s orbit farthest from the sun.
Apogee: The point in a celestial object’s orbit farthest from the earth.
Centripetal force: The force that pulls an object towards the center of its circular path.
Centrifugal force: The force that pushes an object away from the center of its circular path.
Equinoctial tides: Tides that occur near the equinoxes, usually with the highest range.
Impermeable area: Surfaces that do not allow water to pass through, such as roads and rooftops.
Perigee: The point in a celestial object’s orbit closest to the earth.
Perihelion: The point in a planet’s orbit closest to the sun.
Specific gravity: The ratio of the density of a substance to the density of a reference substance, typically water.
Time of concentration: The time it takes for rainfall to flow from the farthest point in a drainage area to a specific point in the sewer system.

Examples:

The Bristol Channel: The Bristol Channel is known for its large tidal range, with the highest tide recorded at Chepstow being 48 feet 6 inches. The channel’s unique geography, with a gradually rising bed and converging channel, leads to an increase in the velocity and rise of the tidal wave.
The Thames River: The Thames River provides an example of how upland water flow impacts sewage dispersal. At Barking, sewage takes approximately 30 days to travel 31 miles to the sea due to the relatively low flow of upland water.
Great Crosby Outfall Sewer: The Great Crosby outfall sewer, which discharges into the Mersey, utilizes greenheart piles for support, sheeting to stabilize the excavation, and steel rails to support the sewer pipes.
Waterloo Sea Outfall: The Waterloo sea outfall utilizes a unique pile-driving technique involving a water jet to drive piles into sand and silt.
Aberdeen Sea Outfall: The Aberdeen outfall sewer features cast iron pipes embedded in a heavy concrete breakwater, showcasing a robust design for resisting wave action.
Windmills: Windmills have been used successfully to pump sewage in small towns, offering a cost-effective alternative to traditional engines.
Diving Inspections: Diving inspections are essential for ensuring the structural integrity of sea outfall structures, particularly during construction.
Leap Weir Storm Overflow: Leap weirs use the velocity of sewage to direct storm water into a separate overflow drain, minimizing the burden on the main sewer.
Diverting Plate Storm Overflow: Diverting plates use a movable plate to direct storm water into an overflow drain, with an inclined screen to remove floating debris.
Box Sextant: Box sextants are used to measure angles between three fixed points on shore to determine the position of a boat or floating object.

Conclusion:

The Sewerage of Sea Coast Towns is a valuable resource for engineers involved in the design and construction of coastal sewage systems. Adams meticulously details the intricate interplay of tides, currents, and rainfall in impacting sewage disposal, emphasizing the importance of careful planning and observation. He also provides valuable insight into the challenges of using concrete in marine environments and the practical considerations involved in pumping sewage using windmills. Ultimately, the book underscores the need for engineers to approach coastal sewage projects with a thorough understanding of the unique conditions present and to employ innovative solutions to ensure effective sewage dispersal and protect public health.

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