Presentation given by Paul Jensen, PBS&J on the Canyon Water ...

Water Quality Assessment and
Regional Facility Planning for
the Canyon Reservoir
Watershed
GBRA and Comal County
with PBS&J
For the
Texas Water Development Board

STUDY BACKGROUND
• Canyon Reservoir is the major water
resource in the basin and has excellent
water quality
• In the past decade population growth in
the immediate watershed has been
rapid, and similar growth is expected
• Concern that water quality could be
impacted was basis for study

BACKGROUND CONTINUED
• There is good water quality today, with
no indication of a recent decline
• Despite recent population growth, there
appear to be few indications of
problems with existing septic systems
• Accordingly, study focused on avoiding
future problems rather than fixing
present problems

Canyon Water Quality Data
1981-1992 1993-2002
TN (mg/L) 220 263
TKN (mg/L) 296 244
TP (mg/L) 53 50
Chl a (mg/L) 3.4 2.0
TSS (mg/L) 5.7 4.1
Secchi Depth (m) 2.3 2.3

POPULATION PROJECTIONS
• Texas State Data Center projections
employed
• High growth scenario used to insure
that study projections would be
conservative

NUTRIENT LOADS CONSIDERED
• Upstream loads from River
• Point source discharges to reservoir
• OSSF loads in study area
• Runoff loads in study area

UPSTREAM LOADS
• Data from Spring Branch gage analyzed
• Average TSS, TN and TP loads/acre
computed
• These loads applied to study area as a
start
• Used to calibrate runoff calculations

RUNOFF LOADS
• Calculated using procedures developed
from City of Austin data
• Adjusted to Spring Branch rate in 2000
• Method quantifies effect of new
development impervious cover and
rapid drainage causing scour of
tributary streams

PERCENTAGE LOAD REMOVAL
BY CANYON RESERVOIR
TSS
TN
TP
All Data
41
38
74
Dry Year
1996
65
64
85
Wet Year
1997
43
87
75

OSSF LOADS
• Calculated from literature values
• Assumed that all worked as intended
• Used conservative flow and
concentration values leaving septic tank
• Assumed 90% removal of nutrients in
drainfield

Projected TSS Load Changes
to Canyon Lake
Projected TSS Load Changes to Canyon Lake
6,000,000
5,000,000
4,000,000
3,000,000
2,000,000
Upstream
Study Area Runoff
WWTP
1,000,000
-
2000 2010 2020 2030 2040

Projected TN Load Changes to
Canyon Lake
Projected TN Load Changes to Canyon Lake
250,000
200,000
150,000
100,000
50,000
Upstream
Study Area Runoff
OSSF
WWTP
-
2000 2010 2020 2030 2040

Projected TP Load Changes to
Canyon Lake
Projected TP Load Changes to Canyon Lake
35,000
30,000
25,000
20,000
15,000
10,000
Upstream
Study Area Runoff
OSSF
WWTP
5,000
-
2000 2010 2020 2030 2040

Projected Load
Figure 5-3
Projected Runoff and Septic TSS, TN, and TP Loads
as % of Existing Loads at Canyon Lake
Projected Load as % of Existing Load
60
40
20
0
T
S
S
T
N
T
P
T
S
S
T
N
T
P
T
S
S
T
N
2000 2010 2020 2030 2040
T
P
T
S
S
T
N
T
P
T
S
S
T
N
T
P
TSS
TN Runoff
TN Septic
TP Runoff
TP Septic

Development Scenarios
• Path A - Continuation of the
present path
• Path B - Regional Plan to
encourage central wastewater
systems on smaller lots and
incorporating Low Impact
Development features.

Elements of Protection Plan
• Wastewater Treatment
– New WWTP
– OSSFs
• Runoff

Regional WWTPs
• For smaller lot developments
• Would be “zero discharge” facilities
emphasizing beneficial reuse:
– Irrigation of parks, commercial properties and golf
courses
– Possible supply to homeowners for irrigation
• Emphasize management <strong>by</strong> public entity
• Majority Steering Committee support
• Minority of Committee opposed

RUNOFF
Low Impact Development
• Minimize impervious areas
• Disconnect impervious area drainage
• Rainwater harvesting
• Bioretention
• Pond retention and irrigation use

IMPLEMENTING LID
• Goal of keeping post-development
runoff the same as pre-development
can be achieved in many ways
• Recommend that developments above a
minimum size be required to have a PE
certify that runoff will be similar to pre-
development condition

QUANTIFYING EFFECTS OF
PLAN
• Existing flood control ordinance will have
some effect in reducing runoff
• Not take effect until 2010 because of backlog
of platted development
• Because most new homes in subdivisions, LID
applied to 75% of population growth
• Central WWTPs assumed to be used in
subbasin 9, with 1 and 10 also candidates

Load with Recommended Plan
Figure 5-4
Projected Runoff and Septic TSS, TN, and TP Loads
as % of Existing Loads at Canyon Lake
with Recommended Action Plan
Projected Load as % of Existing Load
60
40
20
0
T
S
S
T
N
T
P
T
S
S
T
N
T
P
T
S
S
T
N
2000 2010 2020 2030 2040
T
P
T
S
S
T
N
T
P
T
S
S
T
N
T
P
TSS
TN Runoff
TN Septic
TP Runoff
TP Septic

STUDY AREA TN LOAD CHANGES
Load in Kg/Yr
90,000
80,000
70,000
60,000
50,000
40,000
30,000
20,000
10,000
0
TN with No Action Taken
TN with Recommended Action Plan
2000 2010 2020 2030 2040

STUDY AREA TP LOAD CHANGES
35,000
30,000
Load in Kg/Yr
25,000
20,000
15,000
10,000
5,000
0
TP with No Action Taken
TP with Recommended Action Plan
2000 2010 2020 2030 2040

Recommendations
• Low Impact Development
• On-Site Sewage Facilities
• Regional WWTPs
• Environmental Education
• Water Conservation
• Water Quality Protection Zone

OSSF
• Used for greater than 1 acre lots
• Educate on proper maintenance
• Document OSSF failure data

Environmental Education
• Materials on OSSF operation
• LID concepts
• Minimal use of fertilizers & pesticides

Water Conservation
• Native vegetation
• Rainwater harvesting

Water Quality Protection Zone
• Area where recommendations would be
focused
• Regulations could be enforced <strong>by</strong>
County
• May require legislative action to
establish and grant authority to County