Drainage Problems
Running Head: Drainage Problems
Manuel Andrade
Carlos Levy
Tyler Sturdevant
Angelo Torres
Instructor: Gustav Verhulsdonck
ENGL 218 Sec. 2
April 25, 2005
1
Drainage Problems
Table of Content
1. Abstract
pg. 3
2. Introduction
pg. 4
3. Methods
pg. 6
4. Results and Discussion
pg. 8
5. Conclusion
pg. 21
2
Drainage Problems
3
Abstract
Within the greater Mesilla Valley area there has been an increase in precipitation that has
taken the residents of southern New Mexico by surprise. This downpour has been the
sole cause of serious drainage problems that have arisen in the area. This report hopes to
point out the current drainage problems and attempt to come up with appropriate
solutions. One of the main areas of focus includes the low water crossing that is
currently being used to access the Tortugas community behind A-Mountain. Some of the
proposed solutions to the drainage problems discussed include a plan to place culverts
underneath the low water crossings. Lost wages by residents, lost revenue spending for
the city, the ability for future area expansion, and the decrease in potential for injury or
death caused by flooding are also covered in this study.
Drainage Problems
4
Introduction
Whether it is an increase of dancing, or some one in the clouds sure is sad, the
desert dwellers of southern New Mexico have seen an increase saturating rains that leave
their soggy destruction behind. Most of the destruction that people on the roadways
experience is merely an inconvenience that causes the need for a carwash. But for the part
of the population that prefers to try and preserve the rural living experience, these down
pours are causes for loss of income, loss of mobile freedom, and in many cases, their
lives are at risk. As a whole, the Mesilla Valley is in a state of extreme growth, and with
much of the movement headed into the farther reaches of town where precipitation
drainage is of critical importance, the need to identify and resolve current problems can
lead to a decrease in the chance of a catastrophic event.
One of these problems is the current situation on Dripping Springs Rd., near the
Farm and Ranch Heritage museum. What happens in the cases of extreme moisture is that
the watershed leading up to the Organ Mountains brings in a large amount of water to the
low lying valley before. Since nature doesn’t obey traffic laws, this becomes a problem
when the fast running river of water tries to cross Dripping Springs Rd.. The vast amount
of water has kept traffic from crossing on a number of occasions throughout the past
years, leaving the Tortugas community behind the hill immobile.
Another large problem that the stream of water causes is the build-up of water
behind a makeshift dam upstream left by a gravel pit. In this situation, the water saturates
the soil causing a very unstable structure with a very large potential for failure. Failure of
this structure would have the hydraulic thrust to cause vast amounts of damages to
structures downstream, the real storm dam in particular.
Drainage Problems
5
The first problem in need of a solution would be the makeshift dam, solely
because of the lives that are at stake as compared to a few days stuck at home. For a
problem to be solved, it is necessary to know the direct cause of the problem. In our case,
the problem arises from the build up of water during a storm event. The flow comes from
the large watershed that feeds the particular arroyo that moves through our particular site.
This watershed stretches to the crest of the Organ Mountains and covers an area of about
twenty-eight square miles. With such a large area, and quite a steep grade change
throughout the length of the area, this causes a large volume of water to travel a large
distance in a short amount of time. This time could be as little a two hours from top to
bottom of the watershed. In hydrologic standards, this is an extremely high velocity for
flow in an open channel to be traveling without control of that particular channel.
The first form of control that this flow reaches is a wall of soil which carries a
road made near a local gravel pit. This wall acts as a dam for the arriving water, causing a
stop in dynamic hydraulic movement. Since the flow does not decrease at the halt, the
water is confined by nature to convert the incoming kinetic energy into potential energy.
This is achieved by an increase in what is known as hydraulic head. Hydraulic head is a
measure of the potential energy that a certain system of water contains. This is also what
common sense would call a rise in water level. As the water level behind the dam rises,
as does the potential energy of all of the water upstream of it, leading to a lot of force
being held up by the makeshift dam.
Drainage Problems
6
Methods
All designed earthen dams are constructed and designed with the utmost safety in
mind, mainly because of the amount of force that water can produce. All of the soil used
in these dams are put through various saturation and stability tests which are done to
ensure the material will not cause a failure of the entire structure. The construction
process of these dams is also very stringent because of the high damage factor in the
event of failure. There are compaction tests done on many of these dams as little as every
six inches. This means that for every half of a foot of soil the crew puts on, the lift must
pass compaction and moisture tests. These tests are done on the field with powered
equipment by outside engineers brought in to supervise construction. If the lift does not
pass, the soil must be either removed of reprocessed in place, the first method being most
common for financial reasons. The requirements for these tests are administered by the
United States Department of Environmental Maintenance, now a part of the Department
of Conservation. All of the soil tests are regulated by the standards set forth by the United
States Geological Survey.
The design of these dams takes these regulations thoroughly into consideration,
however, the structures are always over designed with a factor of safety of at least two. A
factor of safety represents the ratio of the designed load tolerable over that of the actual
calculated load, meaning the design can handle at least twice as much as it is supposed to
be able to handle. Once again, this is done strictly for safety purposes. It is cause for
alarm that the dam holding back millions of gallons of water was constructed with none
of this in mind. This is because it was not built or designed to hold back any amount of
water whatsoever. If the dam were to fail at a point when the water level is at a
Drainage Problems
7
maximum, which is most common, the results could be catastrophic. With all of the
potential energy of the stored water being released at one time, the hydraulic thrust of the
stream would send an extremely powerful wall of water tumbling downstream. That
amount of water combined with an extreme amount of velocity entering the actual storm
dam downstream would be enough to overwhelm the design, and have a large potential
for failure. The location of the storm dam as well as the amount of water that it holds
back from the valley below, would cause vast amounts of damage as well as perhaps a
loss of human lives, such as the case with the Teton Dam failure that flooded the towns of
Sugar City and Reburg, Idaho in 1976.
What is proposed is a spillway placed within the dam so that the water can be
drained out of the dam, and in essence, never back up. This is to be accomplished by
installing a form of culvert to carry the amount of flow caused by the runoff at the bottom
of the road. In order to figure out the amount of water that these culverts must carry, one
must first figure out the amount of water that is able to travel from every point of the
particular watershed. To do this, a hydraulic system computer program called HEC-hms
was used. This program was developed and is distributed by the Army Corp of Engineers
and is used widely in government as well as private consulting. The program is designed
to calculate watershed characteristics for various landscape regions and is very detailed in
its data input.
A topographic map of the region was obtained via the office of the state engineer
and was plotted on the map in HEC-hms. Soil characteristics such as density, uniformity,
and saturation points were entered in as data into the program. These characteristics were
achieved by performing lab tests at the Soils Engineering Laboratory at New Mexico
Drainage Problems
8
State University. Although various samples were collected and tested, only one set of
data was used because of the consistency of results obtained. The final bit of information
needed to complete the analysis was to enter in precipitation. The average for the area
within the last few years has ranged from about seven to ten inches, with last year being
9.7 in. Hec-hms asks for the average annual precipitation, and then has the option of
running the analysis with many varieties of fluctuations. These fluctuations are what are
known as storms, for this specific situation, the analysis was done using a twenty-five
year storm. A 100-year storm calculation was done, which is used for most major dams,
however, the area would go through a total remodel with the flow produced, so a more
likely storm was used. This amount is common practice in rural design, and is sufficient
for the design.
Results and Discussion
With all of the data complete and the analysis completed, a flow of 1.35 million
gallons per second was obtained. with this flow, it is now possible to find the culvert size
that will accommodate this flow with a factor of safety applied. For this, the basic
hydraulic continuity equation was used to obtain an area of flow with respect to velocity.
The velocity of this is assumed to a certain extent because of the amount of variables that
arise in the basic geography of the open channel, but with water head losses taken into
consideration, the assumption is close enough for design purposes.
Because many types of culverts are available commercially, things such as
financial backing and ease of construction were taken into deep consideration in choosing
the appropriate material. The immediate choice, because of stability and durability was a
series of what are known as box culverts, however, being that the road atop the current
Drainage Problems
9
dam is dirt, and not of major usage, box culverts seem out of the question. This is because
box culverts require more imported material, are more particular in their placement and
construction, and are therefore of larger cost. Since the road is not readily used (as of
now), the next best choice for the conveyance of water would be CSP culverts. CSP
(corrugated steel pipe) culverts are widely used in all types of rural as well as urban
drainage and are a lot less tedious to install as compared to concrete pipe and box
culverts. CSP’s are commercially available in many diameters and are easy to assemble
to make any length necessary.
For the flow produced by the watershed analysis, it was found that a total number
of six 5-ft diameter CSP culverts are needed to carry the flow safely downstream. This
number corresponds to a factor of safety of about 2, which is sufficient by rural design
standards. The placement of these culverts is to be level with the lowest grade along the
bottom, and plane with the widest point of the dam on both sides. This means that the
culverts do not stick out past the dam on either side, and are as low as possible. This is to
ensure there will be no erosion problems on the dam caused by turbulent water. Turbulent
water is a cause of a change, or more literally, a clash of waters at different velocities
and/or directions. Water in this situation can cause a large amount of damage to a
structure that has not been built with erosion in mind. In order to try and accomplish a
smooth flow of water, the entrance into the culverts should be as planed (at the same
level as it’s surrounding) as possible.
The biggest problem with the proposed design is that, within the last six months
of this report, the dam is no longer a dam; it is a tall road with a culvert underneath. It
seems as though Dona Ana County has taken the initiative to try to fix the problem that
Drainage Problems 10
had occurred previously. The maintenance department has gone ahead and installed a 5-ft
diameter CSP culvert at the bottom of the road, allowing the water to drain freely
downstream. The current solution can be seen in the picture below.
Single Culvert
This has been, and will be plenty sufficient for their current situation of the
roadway above as well as Dripping Springs road which lies downstream. The reason that
this fix will be enough is because it is assumed that the “dam” can still hold back water in
cases of extreme moisture, while it drains the basin slowly. This means that the culvert
will be completely submerged during extreme conditions, and that it can drain water fast
enough to keep their level of submergence to a maximum of about two feet depending on
time conditions. This is because as soil saturates, it becomes more lubricated in a sense.
And once the soil is lubricated its internal properties change, one of them being its load
resistance.
For a short time the strength of the soil rises as its moisture content does until it
reaches what is known as degree of saturation. If the soil continues to take in water,
especially with a bit of dynamic head behind it and the weight of the soil above it, the soil
can start to get high pressure water running within it. This high pressure flow is solely
responsible for the internal erosion that follows. The internal erosion usually takes place
Drainage Problems 11
in the soil just around the culvert, mostly on the top and side sections, causing a decrease
in stability around the culvert. This decrease in stability has a tendency to cause the
friction forces between the soil particles themselves and between the soil and the culvert
to decrease which, with enough pressure and duration, the culvert could become
dislodged from the embankment. The large volume of water still passing through the hole
would cause massive amounts of erosion from underneath the roadway in a very short
period of time, guaranteeing the destruction of the roadway above. This large amount of
soil coming down with the river would also cause quite a bit of destruction to some of the
structures downstream. The velocity and volume of water that would be coming down
would be greater than if it were full, as a result it would not be cause for alarm for the
failure of the downstream dam. As of now, there is nothing downstream of the structure
to destroy, so in the result of failure, the damage would be kept to a minimum other than
some minor clean up. This is where the next proposal ties into the present, a change of
the low water crossing on Dripping Springs Rd. just west of the Farm and Ranch
Museum.
The residents of the Tortugas community behind A-Mountain are not strangers to
the power of rushing water. At various times throughout the last few years, many of them
have been witnesses to the river of water across the main byway connecting their home
and the city of Las Cruces. This flow has been enough to keep many of the passersby
from their destination for periods of up to two days and has been the result of many brave
cars who dare to cross getting water past their doors before being swept away by the
currents, left to retrieve when the times are calmer. The crossing for which there is a
proposed solution can be seen below.
Drainage Problems 12
Dripping Springs Rd.
Being that Dripping Springs Rd. is the only major route to a large community that
is continuing to grow at an exponential rate, the need to remedy the current situation is
becoming more and more necessary, especially for the residents of the outlying
community in the case of an emergency. To begin to find a solution for this problem, the
watershed program, HEC-hms, was used. The same watershed was used for the analysis;
however, since the roadway could be considered an only means of connection between
populations, a 100-year storm was used to calculate the flow for the watershed. Using this
amount of precipitation ensures that the design is adequate to withstand any amount of
rain ever recorded in the area.
Drainage Problems 13
Once the flow was obtained via the HEC-hms analysis, the same procedure was
done calculating the area of flow per unit of time under an assumed velocity. Once again,
the velocity was assumed given many considerations including head loss in the channel,
initial velocity, landscape geography, and distance traveled. Although this velocity
cannot be measured very accurately because of the diversity and occurrence of these
flows, the assumed value of approximately 15 feet per second is adequate enough for
design purposes. With the needed area of flow solved for using the hydraulic continuity
equation, it was then matched up as close as possible to some of the more commercially
available types of culverts. Many varieties were considered under the same
considerations that all construction projects are. Things such as current road grade,
current roadway condition, ease of construction, and cost were among the top of the list
of optimum criteria.
With all of the criteria and options put into place, the obvious choice once again
for the best solution was the design of a box culvert system to carry the roadway as it
crosses the natural storm drain. The box culverts were chosen as the proposed design
because of the importance of the roadway as well as the need for a more permanent
structure. The calculated design calls for a system consisting of 6 adjacent culverts each
measuring five feet tall by six feet wide. This system is considerably bigger than the one
proposed for the same watershed just upstream, however, with the use of the bigger flow
during the design of the box culverts the difference is within 62 square feet of flow area.
This proposed solution is also probably the costliest of the choices, but with good
reason for being chosen. The box culverts are built from formed concrete walls and also
contain concrete floors and ceilings which are placed adjacent to one another to form a
Drainage Problems 14
rigid deck on top where a road way can be constructed. These culverts are also very
versatile in size because they are poured in place and can be extended for as long as
necessary. These types of culverts are also more efficient in carrying water than other
materials commercially used because they reduce the head loss caused by friction inside
of a pipe by a considerable amount. This will allow a greater volume of water to pass
through the system per unit of time.
With a box culvert system in place, erosion control is also less of a problem
because the culverts’ inlets are also lined with concrete, making them less susceptible to
uplift from turbulent flow underneath the culvert, in turn reducing the likelihood of
erosion. The culverts also require less maintenance than other systems because of their
large face inlets. These allow debris that is picked up by the flow to pass through the
culvert with less resistance and less chance of becoming lodged within the culvert. When
debris gets stuck internally, it acts like a fish net for any thing else solid that has been
caught by the torrential currents, causing a backup in the pipe, until flow through the
culvert is completely cut off. This reduction in flow area could cause problems for the
entire system if there is enough flow and not enough room. But with concrete box
culverts in place, there is a significantly lower chance of an event such as this occurring
even under extreme conditions. An example of the proposed roadway solution can be
seen below:
Drainage Problems 15
Box Culvert
With a costly improvement to the drainage system, the cost of the roadway going
across the arroyo is also going to come into play. One of the things that make box
culverts even more likable among the design world is that, once in place, the top of the
finished product is optimum for road deck construction. This is a definite advantage in
the ease of construction as well as the versatility. In some cases, with the culverts built
with sufficient height to clear water levels by sometimes as much as six feet, the deck of
the roadway can be poured directly onto the roof of the lie of culverts. But this case
would call for a set of designed soil lifts that would be used for the rest of the roadway.
This would add to the height difference between the top of the roadway and the top of the
dynamic water surface, making sure that the solution would not lead to something similar
to the situation at present.
With a combined system in place we feel that the present danger would be
completely resolved for years to come. However, the idea of going through with a costly
Drainage Problems 16
project such as destroying a roadway, constructing culverts with large amounts of
imported material, and then reconstructing another roadway on top of that, all with the
chance of being destroyed because of a single under designed culvert a short distance
upstream, seems to not be the correct choice of action. As was mentioned before, we feel
that the current situation with the single drainage culvert that has been placed at the
bottom of the “dam” is sufficient enough to take away the risk of serious loss with an
intense amount of precipitation. The danger of a catastrophic failure occurring because of
the previously sealed soil wall was the largest cause for concern, but since that threat has
been resolved, the last real problem at hand is the Tortugas community being trapped on
the wrong side of the road during a sudden downpour.
Whether one has recently seen the amount of houses being constructed in the
deserts behind A-Mountain or not, there is no denying that there is a definite surge in the
migration towards the Organ Mountains. With such a large population already living in
the area, there is no doubt that some of these people enjoy warm showers and food on a
regular basis. But in order to enjoy these pleasantries of life, many of these people have
found that they need to earn money to pay for them by working, many times within the
city limits. With the large amount of construction going on in the area, there are also
many people from within the city limits that make their office in the Tortugas community
for the day. Even though they are construction workers, these people also enjoy the
feeling of hot water and a meal on a daily basis, and in order to do this, they must earn
money in trade for their skills. But on certain rainy days out of the year, there are times
when neither of these people can commute to work, leaving money and time to be lost.
This lost money is not only ever seen by the potential earner, it is also not seen by the
Drainage Problems 17
community in which the money is spent. This loss in revenue trickles down every link of
the financial food chain, never being to an advantage to anyone.
With so much activity brewing behind Aggie Hill, this could start to show its
effects on the entire Mesilla Valley if the problem continues. Even though these are
problems that might not show up very pronounced or regularly, they are nonetheless a
present. With the dramatic increase in moisture within the last two years and the areas
frequency of flash floods, the situation continues to become an inconvenience for more
and more people who must commute through Dripping Springs Rd. Currently, the
situation with the upstream dam has been improved enough to keep the general
population safe and dry, so there is no longer a cause for alarm. But with the surge of
growth encompassing the eastern desert, there is a growing part of the general population
that is still confronted with a potential for loss. Whether or not this amount of loss
surpasses the cost of the resolution is a matter of benefit.
There are approximately five hundred family housing units in the area behind AMountain in the Tortugas community, with many more currently under construction.
Most of these homes are occupied by a family household population. According to the
New Mexico Housing Department, the median family income for the Las Cruces area in
2004 was $37,360. With a safe assumption being that about two-thirds of the population
works and earns the median income, it is found that for every day that water is flowing
over Dripping Springs Rd. refusing people access into town, there is a total of $44,476 in
lost income. This was done by taking two-thirds of the 500 home populations and
multiplying it by the annual income over days worked. The year was made up of 56 five
day weeks. Each employed household stands to lose approximately $133 per day
Drainage Problems 18
stranded. This amount of money can be made up at other times during the year when the
whether is not so unyielding, but the time that is lost can never be made up. In a sense,
the water flowing over the roadway is costing the entire community $44,476 worth of
time everyday that they are denied access across the roadway.
Granted, the entire proposed project would definitely run well over the $44,476
price tag, it can be seen as an investment rather than a capital cost. A cost analysis of the
entire project was not done due to time constraints and violent fluctuations in the price of
building materials at the present time, but an estimate of $350,000 from similar projects
could be considered an accurate price tag.
With a total project estimate at $350,000, this means that the roadway could buy
back all of the time taken in eight days of torrential rain. Although there are many other
factors to consider in the cost-benefit analysis of this project, this small example is only
the bottom rung on the ladder of improvement. The proposed box culvert system was
chosen for durability, versatility and above all, its maintenance efficiency. This means
that the roadway will be practically self maintained, and with very little occurrence of
damage, no further maintenance on the culverts or roadway will be necessary. With a
small upkeep cost, the majority of the project cost will be associated with the capital cost.
Large capital costs are not as pleasing to the pocket book as others because of the
large amount of money that is required in advance. The agency in charge of budgeting
these improvements will have more of a problem trying to allocate money for a project
such as this rather than one with half the capital cost, and twice the maintenance cost.
Only reason being that the price tag on the latter project looks impressively less than that
the lump sum of money needed.
Drainage Problems 19
What many fail to realize, is that a project such as the one proposed will have
only one cost, this cost will cover the structure for its entire extended life. With such an
expensive structure in place downstream, it is suggested that the single culvert already in
place upstream be accompanied with five more just like it in order to ensure the structure
does not fail. With failure of the single culvert, it would be almost inevitable that damage
would be done to the box culvert system and roadway waiting down grade of the wash of
mud and water. This is why it is proposed that as of now, either the entire proposal be
implemented, or left the way it is until something can be done about the entire situation
with one exception.
At present, the flow of water that makes its way over the low water crossing on
Dripping Springs Rd. has began to use its own internal energy to cause the vast erosion
on the downstream side of the road. This current crater can be seen in the picture below.
Once an erosion inspired phenomenon such as this has begun, the problem only gets
progressively worse if nothing else is done. These holes are extremely dangerous as well
as damaging to the roadway because they begin to grow underneath the base lifts of the
road foundation. If they are let alone, they will continue to increase in diameter, causing
the potential for collapse of the roadway next to and above the eroded crater. It makes
common sense that if the roadway collapses, the path will be impassable even in the
driest conditions. This failure would also lead to a great deal of time and money spent on
the reconstruction of the original roadway, and nothing being improved.
Drainage Problems 20
Area of Erosion Caused by
Rainfall
To remedy the current erosion problem currently at work at the low water
crossing, an erosion control material known as rip-rap should be used. To the general
population, rip-rap is nothing more than large pieces of broken concrete, but to the
engineering world, it is the most effective, as well as least expensive form of erosion
control. The hole is to be filled with rip-rap until it is at normal grade with its
surroundings. It is not necessary, but recommended, that the rip-rap be held in place by
wire lath that will keep the fill in place. The lath can be labor intensive to install, but
because of the severity of the current erosion, it is believed that the lath will raise the
factor of safety to an optimum level.
After measurements and volume calculated, it was found that approximately 3
cubic yards of rip-rap are needed to fill the current hole. Since rip-rap is usually junk,
most of it can be acquired for free from construction site. The only cost associated is
hauling the material from site to site. The current rate for such mobility is about $80 per
Drainage Problems 21
cubic yard. This leads to a cost of about $240, plus the lath and labor, if in fact the wire is
used. This is a very minimal cost as compared to the amount of damage that the unremedied problem could and will result in. This proposed idea should be taken into
serious consideration and if at all possible, implemented in the near future.
Conclusion
Mother Nature has been known to unleash her furry at anytime, whether you have
planned a birthday party or you have to be at work in two hours, the earth has no regards
for the plans of her inhabitants. Within a few hours of a southern New Mexico flash
flood, a person can become immobilized and isolated in an area with no choice but too
watch the power of nature cross what was once their path. This has been the case for
many of the residents who live behind A-Mountain in the Tortugas housing community.
They have been no strangers to being stranded, and for the most part, they agree that it is
not a pleasant feeling. With a loss in their income due to their inability to show up for
work, a loss of spent revenue in the Las Cruces community, topped with the danger
involved in a high volume of water crossing the roadway, these people are not in a highquality position. Because of this, a set of six 5x6 ft culverts are proposed to carry the high
flow of storm water downstream to the retention dam, as well as vehicles and their
passengers safely across Dripping Springs Rd. Coupled with the box culvert system, five
more 5-ft diameter CSP culverts are proposed to be installed upstream on the dirt road
“dam” where there is only one.
Since the situation with the retention of water in the makeshift “dam” has been
fixed to a certain extent, the potential for a catastrophic failure has been greatly reduced.
Because there is still a chance for it to collapse, it is recommended that only the eroded
Drainage Problems 22
crater by the current low water crossing be fixed by filling with rip-rap. This is due to the
amount of damage that would result with upstream failure and a lifted roadway. The rest
of the proposed project should be constructed together so as to ensure a safe, effective,
efficient, and satisfactory finished product.
Drainage Problems 23
References
Armen, J.C., & Roybal, A.D. (1984). Handbook of Drainage and Construction Products.
Middletown, OH: Armco
Beck, G.G., & Dobson, C. (1999). Watersheds: A practical handbook for Healthy Water.
Buffalo, NY: Firefly Books
Bloodgood, D. W. (1921). New Mexico Experiment Station. In C.P. Wilson M.S., D.W.
Bloodgood (Eds.), Drainage in The Mesilla Valley of New Mexico: (bulletin no.
129). Las Cruces NM: Rio Grande Republic.
Garcia, A. M. (1991). Peak Discharge and Culvert design for Small Watersheds. Las
Cruces, NM: New Mexico State University.
Permanent Committee of the International Commission on Irrigation and Drainage.
(1980). The Application of Systems Analysis to Problems of Irrigation, Drainage
and Flood Control: A manual for water and agricultural engineers. Oxford, New
York, Toronto, Sydney, Paris, Frankfurt: Pergamon Press.
Portland Cement Association (1987). Handbook of Concrete Culvert Pipe Hydraulics.
Chicago, IL: Portland Cement Association.
U.S. Department of the Interior Bureau of Reclamation. (1978) Drainage Manual: A
water resources technical publication. Washington, D.C.: United States
Government Printing Office.