HomeMy WebLinkAboutCorrespondences445 Chimney Hill Drive
College Station, Texas
77840-5800
13 February 2011
Mayor N. Berry
City of College Station
University Drive
College Station, TX
77840
Dear Mayor Berry:
I am writing today about the proposed development within the Chimney Hill Creek corridor. It is
proposed to replat an area on the northern side of Albertsons'. In order to simplify matters I have
called the creek Chimney Hill. I am writing this letter for two purposes:
1. To object to the development on the grounds of safety for the people who live in the
Chimney Hill Creek corridor, because of the proposed changes brought by the
development as it is immediately downstream of a dam. This dam should be reviewed
by the TCEQ to determine if it is a notifiable dam, within the meaning of the relevant
statute, it is a high hazard dam within the meaning of the TCEQ guidelines.
2. As a Chartered Corporate Member of the Institution of Engineers, Australia as part of my
ethical responsibilities under Section 4 of the organizations code of ethics. These
qualifications are recognized in the USA under the Washington Accord.
The relevant section of the code of ethics is:
4. Promote sustainability
4.1 Engage responsibly with the community and other stakeholders
a) be sensitive to public concerns
b) inform employers or clients of the likely consequences of proposed activities on the
community and the environment
c) promote the involvement of all stakeholders and the community in decisions and processes
that may impact upon them and the environment
4.2 Practise engineering to foster the health, safety and wellbeing of the community and the
environment
a) incorporate social, cultural, health, safety, environmental and economic considerations
into the engineering task
4.3 Balance the needs of the present with the needs of future generations
a) in identifying sustainable outcomes consider all options in terms of their economic,
environmental and social consequences
b) aim to deliver outcomes that do not compromise the ability of future life to enjoy the some
or better environment, health, wellbeing and safety as currently enjoyed.
I am raising the issue of safety associated with the drainage system that has been developed in the
Chimney Hill Creek Catchment within your city as an engineer with expertise in drainage design of
this type. I do not practice in Texas, but under my code of ethics I am bound to now draw this matter
to the attention of the relevant authority.
The areas of specific concern or issues are:
1. A set of two dams has been created within the Chimney Hill Creek Catchment that I am
of the opinion should be referred to the Texas Commission on Environmental Quality for
review now that houses are to be located within the immediate downstream vicinity of
the spillway and the emergency egress for the residents is across the spillway area.
Recent deaths in Toowoomba in Australia and US marines in Japan point to the folly of
developing in these types of urban drainage systems.
2. The spillway design fails to conform to the requirements set out in the TCEQ manual and
fails to conform to what would be considered normal accepted practice for the
discharge point on a dam immediately upstream of residential housing. No notification
system is in place if the dam fails, where new houses will be located immediately below
the dam wall. This is far from normal, when we consider that upward of 24 people will
live in this situation.
3. Adam design, such as this one, is always undertaken using three flow criteria and other
criteria:
a. 1 in 5 to 1 in 25 years
b. 1 in 100 years or what is termed an Act of God level in normal engineering
design, but here is just one of the considered design flows
c. Probable maximum flow which in this area of Texas is between 4 and 5 times the
1 in 100 year flow.
d. Such other criteria as determined by the competent authority, in this case the
analysis that follows provides a standard of 75% of probably maximum flow for
Texas , which for the purposes of this letter is assumed to be 4 times the 1 in
100 year flow, as required it would appear from the TCEQ manual
Issue 1 Dam Safety
TCEQ Requirements are:
299.11. General.
The executive director shall evaluate the hydrologic, hydraulic, and structural adequacy of the dam in
determining whether a proposed or existing dam is considered a deficient dam.
(1) The executive director shall evaluate the hydrologic and hydraulic adequacy of the dam and
spillways using the criteria in the most current version, at the time of the evaluation, of the
agency's Hydrologic and Hydraulic Guidelines for Dams in Texas.
(2) The executive director may also take into consideration the condition of the dam, including
the possibility that the dam might be endangered by:
(A) overtopping,
(e) seepage;
(C) piping;
(D) settlement;
(E) erosion;
(F) cracking,
O lzk W S
(G) sinkholes;
(H) earth movement;
(I) uplift;
(1) overturning,
(K) failure of gates or operation of gates;
(L) failure of spillways,
(M) failure of conduits; or
(N) other conditions, as appropriate.
(a)The executive director shall classify all proposed and existi.
intermediate, or large) and downstream hazard (low, signific
physical condition of the dam.
(b) The executive director may reclassify the hazard classification of a dam at any time based
on:
(1) an inspection and downstream hazard evaluation by the executive director;
(2) a report of an inspection and downstream hazard evaluation by the owner's
professional engineer,
(3) a breach analysis performed by either the executive director or the owner's
professional engineer as described in §299.15(a)(4)(A)(i) of this title (relating to
Hydrologic and Hydraulic Criteria for Dams); or
(4) a review of current aerial photography and topographic maps, along with
information obtained in the field
In terms of the size criteria set out in the TCEQ manual, the major dam in the Chimney Hill
Catchment would fall into the small category considered by the TCEQ in terms of depth and
potential loss of life.
There is an automatic consideration if the dam is over 10 feet high and 50 acre feet in volume. The
dam is over 10 feet in height, it would require a detailed hydraulic analysis using a program such as
HEC-HMS 3.5 to determine the impoundment volume in a PMF storm, however a preliminary review
using the available of the volume within the two linked western impoundment areas suggests that
this question will only be answered with a full analysis completed in accordance with the
requirements of the TCEQ.
I think it is safe to assume until evidence is provided that the total impoundment volume is less than
5o acre ft. that it is assumed to be greater than 50 acre feet for an initial consideration. At that level
of impoundment it is an automatic referral to the TCEQ.
The second consideration is the hazard presented by the dam, as set out in the TCEQ manual as
follows:
299.14. Hazard Classification Criteria.
The executive director shall classify dams for hazard based on either potential loss of human life or
property damage, in the event of failure or malfunction of the dam or appurtenant structures, within
affected developments, that are existing at the time of the classification. The hazard classification
may include use of a breach analysis that addresses the incremental impact of the potential breach
over and above the impact of the flood that may have caused the breach, as defined in
§299.15(a)(4)(A)(i) of this title (relating to Hydrologic and Hydraulic Criteria for Dams). The
classification must be according to the following.
(1) Low. A dam in the low-hazard potential category has:
(A) no loss of human life expected (no permanent habitable structures in the breach
inundation area downstream of the dam), and
(e) minimal economic loss (located primarily in rural areas where failure may
damage occasional farm buildings, limited agricultural improvements, and minor
highways as defined in §299.2(38) of this title (relating to Definitions)).
(2) Significant. A dam in the significant-hazard potential category has:
(A) loss of human life possible (one to six lives or one or two habitable structures in
the breach inundation area downstream of the dam); or
(e) appreciable economic loss, located primarily in rural areas where failure may
cause:
(i) damage to isolated homes,
(ii) damage to secondary highways as defined in §299.2(58);
(iii) damage to minor railroads, or
(iv) interruption of service or use of public utilities, including the design
purpose of the utility.
(3) High. A dam in the high-hazard potential category has:
(A) loss of life expected (seven or more lives or three or more habitable structures in
the breach inundation area downstream of the dam), or
(e) excessive economic loss, located primarily in or near urban areas where failure
would be expected to cause extensive damage to: Texas Commission on
Environmental Quality Page 4 Chapter 299 - Dams and Reservoirs
(i) public facilities;
(ii) agricultural, industrial, or commercial facilities;
(iii) public utilities, including the design purpose of the utility,
(iv) main highways as defined in §299.2(33); or
(v) railroads used as a major transportation system
The dam will fit into the high hazard category as the potential loss of life is, for all those who will live
below the dam wall, is in excess of the number 7 set out in the manual. The economic loss from the
death of the 24 people who will live in the damage breach inundation zone is in the order of $140
million using the US government standards for value of life. A detailed breach analysis is required to
determine the flooded area and also to consider if these people can be evacuated safely.
As the dam is in excess of 10 feet, is located in an urban area and has more than seven people in the
potential breach area of the dam wall that may be subject to significant and immediate flooding with
failure of the wall, then this matter appears to fall within the statutory approval of the Executive
Director of the TCEQ and not Council engineers or the Planning and Zoning Commission of the City
Council. The executive director of the TCEQ has the power to declare the dam as acceptable, but
given the future high hazard potential this is an issue that the executive director of the TCEQ should
decide after reviewing the facts and analysis. I have not been supplied with any information that
gives me any assurance that this analysis has been completed at this date.
Issue 2 Spillway Design
A normal spillway design for a dam such as this is not by overtopping the dam wall, which will drop
clean water onto the foot of the dam, leading to potential white water scour and failure of the dam.
This has occurred on other dams. Figure 1 shows a picture of the dam wall and the surrounding area.
Figure 1 shows the rear of the Albertson's store, which is clearly located on fill, probably obtained
from the excavation for their front parking lot. A low earth wall separates the two impoundment
areas for this dam arrangement, but it is likely to be lost in a PMF storm given the volumes and
slopes involved. Clearly this problem should be addressed in a full hydraulic analysis.
Figure 1 Major Dam Wall and Surrounding Area -,north western side of Alberton's'
There are houses lower than where I am standing on the right hand side within the creek area. The
arrangement of the pipe system from the Albertson's second dam, located on the left hand side of
this photograph, (Figure2), flows into the major dam at the outlet arrangement.
This arrangement of pipes at the outlet to the major dam is shown in Figure 3. Attention is drawn to
the sewer line crossing the outlet mouth.
Figure 2 Detention Basin Wall and Surrounding Area on the eastern side of Albertsons'
Figure 3 Outlet Structure for the second impoundment area of the dam
The area of the main dam has side slopes at 1:1 and the main channel out is a vertical slot in the
wall with a width of about 2 feet, easily subject to blockage. Figure 4 shows this system and the life
safety problems associated with a vertical slot that is two feet wide.
t1 ~r
S ~
ti
t~
Figure 4 Dam Outlet
The white area at the top of Figure 4 is the north face of Albertson's store, built entirely it would
appear on fill. The original creek would appear from the mapping to have past underneath
Alberton's. Finally, the report provided by the Council does not show a breach analysis nor a 75%
PMF analysis as is required by TECQ guidelines. Asa minimum the TECQ letter setting out an
exemption should be included in any report that contains council's standard closure statement on
responsibilities and actions.
Issue 3 Capacity Calculations
Council guidelines provide some standards for determination of the flood flows, but do not
completely cover this type of system subject to design flows in excess of the 1 in 100 year event. In
the brief time available to review this matter the following information was available or could be
easily determined from available literature and mapping.
The Executive Director of the TECQ can require a full report prepared by an engineer registered in
the State of Texas with dam design skills. This letter merely draws attention to the significant issues
in the catchment and asks as to the status of this analysis now that the dam will fall into the high
hazard category if the replat is allowed. Figure 5 shows the pre-existing catchment from a late
1970's topographic map.
Chimney Hill Creels
Dam site
on 's
rr..e..+ p .J\.T E kS((`a".3 ~,1 N
l Ll {.J
l
s
}r
j .
q! Sr !.y } . ~ '.t it4
R
`1i i
.S R' 1 j,
%
hh
r i{ • iy pia'.. .
R. A.f
i
`s
Figure 5 Pre-existing Catchment from a late 1970s plan
Figure 6 shows the current catchment with an overlay of a set of the distinct catchment areas that
drain to Chimney Hill Creek. This data is shown on a base map obtained from the City of College
Station's GIS data set of contours. The contour interval is 2 feet.
Chimney Hill Creek
Dam ® Lower
Dam Upper
Albertson's
Figure 6 Current Catchments and Dams
The catchment model developed for the analysis is shown in Figure 6. Time did not permit me to
complete a HEC-HMS3.5 analysis. A simple analysis used to establish some of the parameters for a
complete analysis is shown below. The analysis of the predevelopment flow at the outlet to the
catchment at the Bryan City limits is shown in Table 1. 1 have assumed that the PMF event will occur
in a period of sustained rainfall and depression storage will be limited and ground inflow capacity
similarly low. This is a reasonable first approximation. I have left the flows as total volumes assuming
a linear rise. Figure 7 shows the catchments boundaries in my simple analysis, the dam location and
Albertson's.
The assumed north for the analysis is up the page.
Table 1 Approximate Flow in Catchment at outlet
Description
Number
Units
Area
89
Acres
Time of Concentration
30
minutes
Rainfall intensity (100 yr)
7
Inches per hour
Rainfall Intensity - PMF1
28
Inches per hour
Total Flow Volume -100 yr
(7/12)2*893 *0.54
Acre feet
Total Flow Volume -100 yr
26
Acre-feet
Total Flow Volume - PMF
(28/12)*89*0.5
Acre-feet
Total Flow Volume - PMF
102
Acre-feet
Dam - lower
Dam - upper
Albertson's
r~ , Fem. ~ Area r
Afe 26 \
Area z^e~ 1 J
i - - iarea.2' Area 18
Ar 25 Area 20
1 % Area 21a
~r 21 Area 17
$ =Arc 22 Area 16
i 71
Figure 7 Current catchments
r
' Assuming no change in time of concentration, some authorities would reduce the time of concentration.
2 Feet
3 Land area in acres
4 Total flow duration in hours
The Dam is located at the intersection of Areas 21, 20 and 16. The catchment has a a very high level
of impervious catchment as it is essentially commercial areas and parking lots upstream of the outlet
to the dam.
Figure 8 shows the watercourse downstream of the dam, and immediately upstream of the first
existing and recently constructed dwelling on the eastern side of the catchment- My head is above
the floor level of the dwelling behind me. The creek clearly meets the definition of a watercourse as
set out in Howarth's recent monograph and Angel's19th century monograph on this matter. There
are bed, banks and a constant flow of water. I have never seen the creek dry.
The proposed development is on the right hand side of this picture.
I will forward a copy of this letter to the Executive Director of the TCEQ, as this nneets my obligation
under the code of ethics for my Certifying Professional Organization. I believe from my simple
analysis that the Executive Director is the appropriate statutory authority and not the council in this
matter: 1 could be proven wrong, but it appears to my limited reading of thestatute that is a decision
for the director and the director only. He may decline to act, but that is also his decision.
I am sending a copy to my local Homeowners Association as they are dealing with this matter on
behalf of the neighbourhood. I will advise them that I do not believe you have the statutory power
to replat and thus increase the number of people at risk below the dam without TCEQ approval. You
Figure 8 Existing Creek located about 250 yards downstream of the dam mouth.
1
may have this approval, but there is no evidence of this approval in the documentation I have seen
to date. I will be suggesting to the Homeowners Association that they request this documentation.
I appreciate this is a difficult matter, but it not of our making, but comes about from decisions made
before our time of involvement. I am also aware of the tragedy of the loss of life in floods, that are
usually preventable, having been involved in several matters on drainage that were subject to
litigation.
I will suggest to the Home Owners Association that they request a meeting with the Director and you
at your earliest convenience. Whilst I understand you have recused yourself from the replat, I
consider that you need to be involved in the discussions on the dam, as until this is resolved I fail to
see.how the matter can be considered by Council at this time.
Yours faithfully
Digitally signed by John Nichols
IN: cn=John Nichols, o, ou,
John Nichols email=jm.nichols1956@gmail.com,
c=US
Date: 2011.02.16 13:26:28 -06'00'
John Nichols, BE, PhD, MIE(Australia),
Chartered Professional Engineer
r
Dr. John M. Nichols
445 Chimney Hill Drive
College Station
Texas 77840-5800
30 December 2010
The Mayor
City of College Station
1101 Texas Avenue
College Station
Texas
Dear Mayor Berry:
I normally do not become involved in local politics because of my prior work for local government
authorities for many years on drainage, planning and transportation matters. Since 1 moved with my
family to College Station in 20021 have only corresponded with the Mayor on a single occasion
about a development issue in Chimney Hill. The previous letter concerned the rezoning application
for a block of land atthe end of Chimney Hill, which occurred I believe in the last two years.
1 assume that my previous letter on this matter is available to you, so that I do not have to repeat all
of the calculations and observations about this matter. In my previous letter, I raised a number of
matters about the drainage for this land at the western end of Chimney Hill Drive, which is a part of
the general drainage system for the area immediately upstream of the proposed development of
land.
I have reviewed the current application information available and again raise the following concerns
about this property:
1. As a home owner I am situated about 60 metres from the land in question. In all the time
this applicant has tried to rezone the property, the applicant has never made any attempt to
contact either myself or I believe our home owners associations. Considering the severity of
the concerns I raised about the drainage in my last letter, and given the distinctive change in
nature of the proposed development from the current character of the area, one would
assume that good planning practice would be to sit down with the local population to listen
to their concerns. A second point is to address the planning issues in advance not in arrears.
2. The plan forwarded by Council shows a purported 100 year flood line.
3. A watercourse flows through this proposed development site, and in the strict legal sense
this unnamed watercourse is defined in accordance with the common law definition of a
watercourse, being bed, banks and water. This watercourse meets these criteria, as I have
never observed the watercourse dry. A watercourse is by definition in the 100 year flood
plain, as the 100 year flood plain concept was developed to overcome the limitations of the
common law. I would refer you to Howarth's book and Angel's book on this matter, which as
far as I understand from my time in courts on these types of matters are the definitive
tracts.
At
4. A significant portion of this land is below the legal definition for a 100 year flood plain and as
such should be excluded from development.
5. At some point, before I arrived in College Station, a detention basin was erected at the
immediate upstream end of the subject property. The detention basin has:
a. Dangerous side slopes, much steeper than is normally allowed for in this type of
design
b. A depth well past the drowning level for young children, which again is a problem if
one considers that we should be designing to accepted standards
c. An outlet that has a strong potential for white water scour and is not designed for
child safety. White water scour is a particularly nasty form of erosion that occurs in
large storm events at the downstream end of hydraulic structures, such as is
constructed in reinforced concrete at the western end of Chimney Hill.
d. This type of scour has the potential to undermine the wall, with serious
consequences for all downstream.
e. Excessive velocities and depths at the outlet, given its position next to a park area,
again well outside accepted standards
f. This is not the only location in College Station that has hydraulic structures that
present a clear and present danger to children, the elderly and the sick.
6. The drainage system needs to be designed for the lots before the land is subdivided so that
Council has obtained sufficient land for the works. The cost for an acceptable drainage
system will be significantly greater than the return on the land.
I have completed many of these cost studies, and would never have recommended that any of my
clients touch such a block of land.
In the end, it would appear that the land owner will learn the true cost of the drainage system and
will, either not proceed or assume that council will ultimately bear the cost. I fail to see why the
citizens of College Station should accept a liability that will run to at least six figures. It would be
cheaper to purchase the lot and turn it into parkland - detention basin, serving the community.
I would suggest that the matter be deferred until these issues can be addressed. I also suggest that
the applicant meet with the local associations to try and understand their perspective.
Yours faithfully
John Ni hols, BE, MIE(Aust),Chartered Professional Engineer