**Barton Springs Residential**

This scenario is intended to be used as a surrogate for all
urban/suburban home and residential uses in the Barton Springs Segment
(BSS) of the Edwards Aquifer. The intention is to couple the edge of
field concentrations from this scenario with the edge of field
concentrations from the impervious surface scenario for Barton Springs
to generate weighted concentrations for areas of varying impervious
cover. Some estimates of impervious fractions in suburban watersheds of
the BSS have been compiled in a City of Austin (COA 2002) report for the
COA jurisdictional section of the Barton Springs Zone (BSZ) and from
local runoff studies obtained from the COA. Within the city of Austin
Jurisdiction of the Barton Springs Zone approximately 7.5% or 5098 acres
consists of impervious surfaces. Within the recharge zone, the city of
Austin restricts impervious cover for new development to 15% of the net
site area and 20% of the site area in the Barton Creek contributing zone
(City of Austin, 2002). However, based on unpublished data obtained from
the City of Austin some residential watersheds in the area may be as
high as 40% (Rich Robinson, COA, personal communication).

  ------------------ -------------- ------------ ------------- -------------- -------------- ---------------
  **Estimates of                                                                             
  impervious                                                                                 
  fractions for                                                                              
  selected                                                                                   
  residential                                                                                
  watersheds in the                                                                          
  area of the BSS.                                                                           
  Obtained from City                                                                         
  of Austin,                                                                                 
  unpublished data                                                                           
  (Rich Robinson,                                                                            
  personal                                                                                   
  communication)**                                                                           

  **Site Name**      **Impervious   **Drainage   **Land Use**  **Recharge**   **Latitude**   **Longitude**
                     Cover**        Area                                                     
                                    (acres)**                                                

  Lost Creek         0.22           209.9        Single Family No             30.28          97.84
  Subdivision                                    Residential                                 

  Rollingwood        0.26           62.9         Single Family Yes            30.27          97.77
                                                 Residential                                 

  Travis Country     0.37           40.7         Single Family Yes            30.25          97.82
  Channel                                        Residential                                 

  Travis Country     0.41           41.6         Single Family Yes            30.24          97.82
  Pipe                                           Residential                                 
  ------------------ -------------- ------------ ------------- -------------- -------------- ---------------

Soils were selected based on vulnerability and the extent within single-
and multi-family residential areas in BSS. Based on a geospatial
analysis of soils (USDA 2006) and land use data (USGS 2003) for
residential areas as well as conversations with local soil experts,
Brackett soils were chosen to represent residential areas in the BSS
(Table 5). Brackett soils are found in both the contributing and
recharge zones of the Edwards Aquifer and are the most common soil on
which residential dwellings are located, accounting for 35% of all soils
in residential areas (USDA 2006; USGS 2003). Brackett soils are often
undulating (Soil Survey Staff 2006) making them desirable for
development due to their scenic nature (Volente 2004). The location of
Brackett soils was also cross-checked with aerial photography to ensure
that the soil chosen coincided with residential areas where pesticides
would reasonably be applied. A local soil expert also confirmed that
Brackett soil is a common soil type in residential areas of the BSS
(Perez, 2006).

The Brackett series represents the 90^th^ percentile of vulnerability in
drainage, erodibility, and slope. These soils are loamy, carbonatic,
thermic, shallow Typic Haplustepts which consists of very shallow to
shallow soils over bedrock. These well drained and moderately permeable
soils formed in residuum over chalky limestone bedrock (USDA 2001).
Brackett is a Hydrologic Group C soil which accounts for approximately
47% of residential soils in drainage. Brackett soils have a USLE K
factor of 0.37 which includes the 90^th^ percentile of these soils in
erodibility (Table 5). Slopes range from 1 to 60 percent (Soil Survey
Staff, 2006); however the most typical range for the Brackett series in
residential areas is 1-12 percent (USDA 2006; USGS 2003).

Crop parameters have been chosen to reflect residential turf areas,
primarily lawns, within the BSS.

The meteorological station selected for this scenario is located in
Austin, Texas. This station is the closest available weather station
that includes data required for PRZM.

+-----------------+----------+-----------------------------------------+
| **Table 1. PRZM |          |                                         |
| 3.12 Climate    |          |                                         |
| and Time        |          |                                         |
| Parameters for  |          |                                         |
| Barton Springs, |          |                                         |
| TX.**           |          |                                         |
+-----------------+----------+-----------------------------------------+
| **Parameter**   | *        | **Source/Comments**                     |
|                 | *Value** |                                         |
+-----------------+----------+-----------------------------------------+
| Starting Date   | Jan. 1,  | Meteorological File from Austin, TX     |
|                 | 1961     | (W13958)                                |
+-----------------+----------+-----------------------------------------+
| Ending Date     | Dec. 31, | Meteorological File from Austin, TX     |
|                 | 1990     | (W13958)                                |
+-----------------+----------+-----------------------------------------+
| Pan Evaporation | 0.69     | PRZM Manual Figure 5.1 (EPA 1998).      |
| Factor (PFAC)   |          |                                         |
+-----------------+----------+-----------------------------------------+
| Snowmelt Factor | 0.36     | PRZM Manual, Table 5.1 (EPA 1998).      |
| (SFAC)          |          |                                         |
+-----------------+----------+-----------------------------------------+
| Minimum Depth   | 25       | Mid point of range (20-30), PRZM        |
| of              |          | Manual, Figure 5.2 (EPA 1998).          |
|                 |          |                                         |
| Evaporation     |          |                                         |
| (ANETD)         |          |                                         |
+-----------------+----------+-----------------------------------------+

  ----------------- ------------- ------------------------------------------
  **Table 2. PRZM                 
  3.12 Erosion and                
  Landscape                       
  Parameters for                  
  Barton Springs --               
  residential.**                  

  **Parameter**     **Value**     **Source/Comments**

  Method to         4 (MUSS)      Default value.
  Calculate Erosion               
  (ERFLAG)                        

  USLE K Factor     0.37 tons     NRCS Soil Data Mart Database for
  (USLEK)           EI^-1^\*      Brackett-Rock outcrop-complex, 1-12%
                                  slopes, Travis County, TX.
                                  (<http://soildatamart.nrcs.usda.gov/>).

  USLE LS Factor    1.34          Calculated according to Haan and Barfield
  (USLELS)                        (1978) equation: LS =
                                  ((λ/72.6)^m^)((430x^2^ + 30x +
                                  0.43)/6.613), where λ = slope length, x =
                                  SLP/100 and m = constant. In this case, λ
                                  = 400 m (default value) and m = 0.5 (EPA
                                  2004).

  USLE P Factor     1             No contour plowing is expected (EPA 2004).
  (USLEP)                         

  Field Area        10 ha         Default value for standard ecological pond
  (AFIELD)                        (EPA, 2004).

  NRCS Hyetograph   4             PRZM Manual, Figure 5.12 (EPA, 1998).
  (IREG)                          

  Slope (SLP)       6 %           Brackett-Rock Outcrop-Complex slope range
                                  1-12% (USDA 2006).

  Hydraulic Length  356 m         Default value for standard ecological pond
  (HL)                            (EPA, 2004)

  Irrigation Flag   1             Homeowners irrigate year round. Kathy
  (IRFLAG)                        Shay, Water Quality Education Manager,
                                  City of Austin Watershed Protection and
                                  Development Review Board, (512-974-2446).

  Irrigation Type   3 (sprinkler) Kathy Shay, City of Austin; and Irrigation
  (IRTYP)                         Guidance for developing PRZM Scenarios,
                                  Table 3; (EPA 2005).

  Leaching Factor   0.1           Irrigation Guidance for developing PRZM
  (FLEACH)                        Scenario, Table 3; (June 15, 2005).

  Fraction of Water 0.95          Irrigation Guidance for developing PRZM
  Capacity when                   Scenario, Table 3; (EPA 2005). BSS
  Irrigation is                   homeowners typically irrigate 3 days/week,
  Applied (PCDEPL)                regardless of available water capacity.

  Maximum Rate at   0.032 cm      Homeowners in the BSS typically apply
  which Irrigation  hr^-1^        about twice as much as the recommended ¾
  is Applied                      inch of water every five days. RATEAP
  (RATEAP)                        value is for 1.5 inches per 5 days (0.3
                                  in/day). Karen Stewart, City of Austin
                                  Water Conservation Department,
                                  (512-974-2978). Irrigation Guidance for
                                  developing PRZM Scenario, Table 1; (EPA
                                  2005).

  \* EI = 100                     
  ft-tons \* in/                  
  acre\*hr                        
  ----------------- ------------- ------------------------------------------

+-----------------+----------+-----------------------------------------+
| **Table 3. PRZM |          |                                         |
| 3.12 Crop       |          |                                         |
| Parameters for  |          |                                         |
| Barton Springs  |          |                                         |
| --              |          |                                         |
| residential.**  |          |                                         |
+-----------------+----------+-----------------------------------------+
| **Parameter**   | *        | **Source/Comments**                     |
|                 | *Value** |                                         |
+-----------------+----------+-----------------------------------------+
| Initial Crop    | 1        | Default value                           |
| (INICRP)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Initial Surface | 2        | 2 = cover crop. Cover crops are         |
| Condition       |          | typically planted in residential areas  |
|                 |          | to keep lawns green when grass goes     |
| (ISCOND)        |          | dormant (Karen Stewart, Senior Water    |
|                 |          | Conservation Specialist, City of Austin |
|                 |          | Water Utility, Date: 3/23/06, Phone:    |
|                 |          | 512-974-2978).                          |
+-----------------+----------+-----------------------------------------+
| Number of       | 1        | Set to number of crops in simulation.   |
| Different Crops |          | Default value.                          |
| (NDC)           |          |                                         |
+-----------------+----------+-----------------------------------------+
| Number of       | 30       | Set to weather data in meteorological   |
| Cropping        |          | file: Austin, TX (W13958).              |
| Periods (NCPDS) |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum         | 0.15     | Expected to be in the range of highly   |
| rainfall        |          | managed turf (0.10 as cited in PA turf  |
| interception    |          | and FL turf scenarios) and non-managed  |
| storage of crop |          | grasses (0.20 as cited in Dunne and     |
| (CINTCP)        |          | Leopold, 1978).                         |
+-----------------+----------+-----------------------------------------+
| Maximum Active  | 15 cm    | Based on managed turf grasses (Nick     |
| Root Depth      |          | Smithamn, Superintendent of Austin      |
| (AMXDR)         |          | Municipal Golf Courses, Date: 3-16-06,  |
|                 |          | Phone: 512-447-2616)                    |
+-----------------+----------+-----------------------------------------+
| Maximum Canopy  | 100%     | Assumes complete turf grass coverage    |
| Coverage        |          | for lawns.                              |
| (COVMAX)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Soil Surface    | 2        | 2 = cover crop. Cover crops are         |
| Condition After |          | typically planted in residential areas  |
| Harvest (ICNAH) |          | to keep lawns green when grass goes     |
|                 |          | dormant (Karen Stewart, Senior Water    |
|                 |          | Conservation Specialist, City of Austin |
|                 |          | Water Utility, Date: 3/23/06, Phone:    |
|                 |          | 512-974-2978).                          |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 1/1/1961 | The average first and last frost dates  |
| Emergence       |          | of the winter season are November 10    |
|                 |          | and March 10, respectively (Karen       |
| (EMD, EMM,      |          | Stewart, Senior Water Conservation      |
| IYREM)          |          | Specialist, City of Austin Water        |
|                 |          | Utility, Date: 3/23/06, Phone:          |
|                 |          | 512-974-2978). Lawn grass goes dormant  |
|                 |          | after the first frost.                  |
|                 |          |                                         |
|                 |          | This scenario was modeled as year round |
|                 |          | coverage.                               |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 1/2/1961 |                                         |
| Maturity        |          |                                         |
|                 |          |                                         |
| (MAD, MAM,      |          |                                         |
| IYRMAT)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 31       |                                         |
| Harvest         | /12/1961 |                                         |
|                 |          |                                         |
| (HAD, HAM,      |          |                                         |
| IYRHAR)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Dry     | 0.0      | Not used in scenario.                   |
| Weight (WFMAX)  |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Canopy  | 7.6 cm   | Karen Stewart, City of Austin Water     |
| Height (HTMAX)  |          | Conservation Department,                |
|                 |          | (512-974-2978).                         |
+-----------------+----------+-----------------------------------------+
| SCS Curve       | 83, 83,  | TR-55 (Table 2-2a). Composite CN for ¼  |
| Number (CN)     | 83       | acre residential lot assuming 38%       |
|                 |          | average impervious area. Assumes year   |
|                 |          | round turf (lawn) coverage with         |
|                 |          | pervious curve number = 74. (USDA,      |
|                 |          | 1986).                                  |
+-----------------+----------+-----------------------------------------+
| Manning\'s N    | 0.110    | San Antonio Hay/Grass (I93HGHGC).       |
| Value (MNGN)    |          | Represents cover code 2 for first year  |
|                 |          | hay/grass, moderately dense cover.      |
+-----------------+----------+-----------------------------------------+
| USLE C Factor   | 0.000 -- | San Antonio Hay/Grass (I93HGHGC)        |
| (USLEC)         | 0.004    |                                         |
+-----------------+----------+-----------------------------------------+

+---------+-------------------+---------------------------------------+
| **Table |                   |                                       |
| 4. PRZM |                   |                                       |
| 3.12    |                   |                                       |
| "Bracke |                   |                                       |
| tt-Rock |                   |                                       |
| Ou      |                   |                                       |
| tcrop-C |                   |                                       |
| omplex" |                   |                                       |
| Soil    |                   |                                       |
| Par     |                   |                                       |
| ameters |                   |                                       |
| for     |                   |                                       |
| Barton  |                   |                                       |
| S       |                   |                                       |
| prings, |                   |                                       |
| TX -    |                   |                                       |
| residen |                   |                                       |
| tial.** |                   |                                       |
+---------+-------------------+---------------------------------------+
| **Para  | **Value**         | **Source/Comments**                   |
| meter** |                   |                                       |
+---------+-------------------+---------------------------------------+
| Total   | 48 cm             | Brackett-Rock outcrop-complex, 1-12%  |
| Soil    |                   | slopes, Travis County, TX. NRCS Soil  |
| Depth   |                   | Data Mart Database                    |
| (CORED) |                   | (<                                    |
|         |                   | http://soildatamart.nrcs.usda.gov/>). |
|         |                   |                                       |
|         |                   | According to an extension agent (Cris |
|         |                   | Perez), residential areas reside on a |
|         |                   | variety of soils. Brackett is a       |
|         |                   | common soil type of residential areas |
|         |                   | in the BSS.                           |
|         |                   |                                       |
|         |                   | Top horizon split in two and thatch   |
|         |                   | layer added as HORIZN 1. Soil         |
|         |                   | parameters of HORIZN 1 according to   |
|         |                   | EPA guidance on development of turf   |
|         |                   | scenario, which is appropriate for    |
|         |                   | modeling residential lawns.           |
|         |                   |                                       |
|         |                   | Additional data were listed for a     |
|         |                   | 5^th^ HORIZN. However, these were not |
|         |                   | included in this soil profile since   |
|         |                   | the 5^th^ HORIZN is composed of       |
|         |                   | bedrock.                              |
|         |                   |                                       |
|         |                   | PRZM Scenario Guidance (2004).        |
|         |                   |                                       |
|         |                   | Adjusted using the relationship % OC  |
|         |                   | = % Organic Matter/1.724 (Doucette    |
|         |                   | 2000).                                |
+---------+-------------------+---------------------------------------+
| Number  | 4                 |                                       |
| of      |                   |                                       |
| H       |                   |                                       |
| orizons |                   |                                       |
| (       |                   |                                       |
| NHORIZ) |                   |                                       |
+---------+-------------------+---------------------------------------+
| Horizon | 2 cm (HORIZN =1)  |                                       |
| Th      |                   |                                       |
| ickness | 10 cm (HORIZN =2) |                                       |
| (THKNS) |                   |                                       |
|         | 5 cm (HORIZN =3)  |                                       |
|         |                   |                                       |
|         | 31 cm (HORIZN =4) |                                       |
+---------+-------------------+---------------------------------------+
| Bulk    | 0.37 g/cm3        |                                       |
| Density | (HORIZN = 1)      |                                       |
| (BD)    |                   |                                       |
|         | 1.4 g/cm3 (HORIZN |                                       |
|         | =2)               |                                       |
|         |                   |                                       |
|         | 1.4 g/cm3 (HORIZN |                                       |
|         | =3)               |                                       |
|         |                   |                                       |
|         | 1.43 g/cm3        |                                       |
|         | (HORIZN =4)       |                                       |
+---------+-------------------+---------------------------------------+
| Initial | 0.47 cm3/cm3      |                                       |
| Water   | (HORIZN =1)       |                                       |
| Content |                   |                                       |
| (THETO) | 0.28 cm3/cm3      |                                       |
|         | (HORIZN =2)       |                                       |
|         |                   |                                       |
|         | 0.28 cm3/cm3      |                                       |
|         | (HORIZN =3)       |                                       |
|         |                   |                                       |
|         | 0.252 cm3/cm3     |                                       |
|         | (HORIZN =4)       |                                       |
+---------+-------------------+---------------------------------------+
| Comp    | 0.1 cm (HORIZN =  |                                       |
| artment | 1)                |                                       |
| Th      |                   |                                       |
| ickness | 5 cm (HORIZN = 2) |                                       |
| (DPN)   |                   |                                       |
|         | 5 cm (HORIZN = 3) |                                       |
|         |                   |                                       |
|         | 1 cm (HORIZN = 4) |                                       |
+---------+-------------------+---------------------------------------+
| Field   | 0.47 cm3/cm3      |                                       |
| C       | (HORIZN =1)       |                                       |
| apacity |                   |                                       |
| (THEFC) | 0.28 cm3/cm3      |                                       |
|         | (HORIZN =2)       |                                       |
|         |                   |                                       |
|         | 0.28 cm3/cm3      |                                       |
|         | (HORIZN =3)       |                                       |
|         |                   |                                       |
|         | 0.252 cm3/cm3     |                                       |
|         | (HORIZN =4)       |                                       |
+---------+-------------------+---------------------------------------+
| Wilting | 0.27 cm3/cm3      |                                       |
| Point   | (HORIZN =1)       |                                       |
| (THEWP) |                   |                                       |
|         | 0.164 cm3/cm3     |                                       |
|         | (HORIZN =2)       |                                       |
|         |                   |                                       |
|         | 0.164 cm3/cm3     |                                       |
|         | (HORIZN =3)       |                                       |
|         |                   |                                       |
|         | 0.145 cm3/cm3     |                                       |
|         | (HORIZN =4)       |                                       |
+---------+-------------------+---------------------------------------+
| Organic | 7.5 % (HORIZN =   |                                       |
| Carbon  | 1)                |                                       |
| Content |                   |                                       |
| (OC)    | 1.16 % (HORIZN    |                                       |
|         | =2)               |                                       |
|         |                   |                                       |
|         | 1.16 % (HORIZN    |                                       |
|         | =3)               |                                       |
|         |                   |                                       |
|         | 0.73 % (HORIZN    |                                       |
|         | =4)               |                                       |
+---------+-------------------+---------------------------------------+

  -----------------------------------------------------------------------------------------------------------------
  **Table 5.                                                                                               
  Soils                                                                                                    
  co-located                                                                                               
  with single-                                                                                             
  and                                                                                                      
  multi-family                                                                                             
  residential                                                                                              
  areas in the                                                                                             
  Barton Spring                                                                                            
  Segment based                                                                                            
  on USDA 2006                                                                                             
  soils data and                                                                                           
  USGS 2003 land                                                                                           
  use data.**                                                                                              
  -------------- ----------- -------- ------------ -------- ----------- -------- ------- -------- -------- --------
  **Soil**       **Total     **%      **Drainage   **KF**   **Slope**   **pH**   **OM    **Sand   **Silt   **Clay
                 Acreage**   Area**   Class**                                    (%)**   (%)**    (%)**    (%)**

  Brackett       10,044      34.8%    C            0.37     1 - 12      8        2       34       38       28

  Tarrant        3,322       11.5%    D            0.32     5 - 18      8        5       22       28       50

  Speck          2,594       9.0%     D            0.32     1 - 3       7        2       34       37       30

  Real           1,891       6.6%     D            0.28     1 - 8       8        6       36       34       31

  Comfort        1,869       6.5%     D            0.32     1 - 8       8        6       28       29       43

  Urban land     1,269       4.4%     D            0.00     0 - 6       0        0       0        0        0

  Rumple         1,120       3.9%     C            0.32     1 - 8       7        2       34       37       30

  Eddy           959         3.3%     C            0.32     1 - 3       8        1       38       36       26

  Volente        832         2.9%     C            0.32     1 - 8       8        3       7        54       39

  Doss           819         2.8%     D            0.32     1 - 5       8        2       7        49       44

  Denton         544         1.9%     D            0.32     1 - 3       8        3       6        48       46

  Purves         448         1.6%     D            0.32     1 - 5       8        3       23       29       48

  Crawford       357         1.2%     D            0.32     0 - 1       7        2       22       28       50

  Austin         343         1.2%     C            0.32     1 - 3       8        3       7        48       45

  Krum           315         1.1%     D            0.32     0 - 1       8        2       26       29       45

  Houston Black  308         1.1%     D            0.32     1 - 3       8        3       17       28       55

  San Saba       307         1.1%     D            0.32     1 - 2       8        3       18       29       53

  Heiden         188         0.7%     D            0.32     1 - 3       8        3       22       28       50

  Bolar          173         0.6%     C            0.32     1 - 3       8        2       34       37       30

  Sunev          163         0.6%     B            0.32     0 - 1       8        2       18       52       30

  Medlin         159         0.5%     D            0.32     1 - 8       8        2       22       28       50

  Tarpley        149         0.5%     D            0.32     1 - 3       7        3       30       30       40

  Castephen      130         0.4%     C            0.32     3 - 5       8        2       34       32       34

  Lewisville     117         0.4%     B            0.32     0 - 1       8        2       8        51       41

  Anhalt         94          0.3%     D            0.32     1 - 3       7        3       26       29       45

  Alluvial land  87          0.3%     A            0.15     0 - 1       8        1       90       0        5

  Patrick        85          0.3%     B            0.32     2 - 5       8        2       28       29       43

  Gruene         59          0.2%     D            0.28     1 - 5       8        2       28       29       43

  Eckrant        28          0.1%     D            0.32     8 - 40      8        7       22       28       50

  Ferris         26          0.1%     D            0.32     8 - 20      8        1       18       29       53

  Orif           17          0.1%     A            0.28     0 - 1       8        2       82       9        9

  Altoga         16          0.1%     C            0.32     3 - 6       8        1       7        48       45

  Oakalla        10          0.0%     B            0.32     0 - 1       8        4       18       48       34

  Seawillow      9           0.0%     B            0.32     1 - 3       8        1       35       34       31

  Tinn           6           0.0%     D            0.32     0 - 1       8        3       22       28       50

  Travis         3           0.0%     C            0.24     1 - 8       7        1       66       19       15

  Hardeman       3           0.0%     B            0.24     3 - 12      8        1       66       20       14

  Whitewright    2           0.0%     C            0.32     1 - 5       8        1       31       33       37

  Gaddy          2           0.0%     A            0.17     0 - 1       8        0       84       7        10

  Bergstrom      1           0.0%     B            0.32     0 - 2       8        2       7        62       31

  Boerne         0           0.0%     B            0.28     1 - 3       8        1       65       20       16
  -----------------------------------------------------------------------------------------------------------------

**Uncertainties**

It should be noted that the BSS is presently, and expected to continue
to be under heavy development pressure (City of Austin, 2002). Although
every attempt was made to select representative soils in residential
areas that would also yield high end runoff and erosion rates based on
the best available data, it is possible that not all soils in
residential areas have been considered due to new development since the
publication of the USGS land cover data set (USGS 2003) which is
generally representative of land cover in 1996.

[Curve Number]{.underline} -- Uses a high end percent impervious area in
TR-55 (USDA 1986) based on unpublished data from COA (Rich Robinson,
Personal Communication). However, within the city of Austin Jurisdiction
of the Barton Springs Zone data suggest that impervious area may be as
low as 7.5% (or 5098 Acres). Within the recharge zone, the city of
Austin restricts impervious cover for new development to 15% of the net
site area and 20% of the site area in the Barton Creek contributing zone
(COA, 2002).

[Irrigation parameters]{.underline}: During the dry summer months, BSS
homeowners use about 12 inches of water per month which is double the
usage of other homeowners that time of year (Stewart, 2006). RATEAP
would therefore be slightly higher during very dry periods: 12 in/mo ≈
0.4 in/day = 0.042 cm/hr. Homeowners apply less water in the winter
months. Actual data for the available water capacity that would trigger
irrigation (PCDEPL) is not available for residential uses. BSS
homeowners typically irrigate 3 days/week, regardless of available water
capacity (Stewart, 2006). PCDEPL was set to 0.95 in order to trigger
irrigation every day at the daily average irrigation rate.

**References**

Austin, City of (COA). 2002. Barton Springs Zone Scientific Inventory.
City of Austin Watershed Protection Department. Environmental Resources
Management Division. Available on-line at
<http://www.cityofaustin.org/.>

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