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Barton Springs Salamander - Residential

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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 However, based on unpublished data obtained from the City of Austin some residential watersheds in the area may be as high as 40% (Rich Robinson, COA, personal communication).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Obtained from City of Austin, unpublished data (Rich Robinson, personal communication)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 NameImpervious Cover Drainage Area (acres)Land Use RechargeLatitudeLongitude
Lost Creek Subdivision 0.22209.9Single Family Residential No30.2897.84
Rollingwood 0.2662.9Single Family Residential Yes30.2797.77
Travis Country Channel 0.3740.7Single Family Residential Yes30.2597.82
Travis Country Pipe 0.4141.6Single Family Residential Yes30.2497.82

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 90th 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 90th 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.
ParameterValue Source/Comments
Starting Date Jan. 1, 1961 Meteorological File from Austin, TX (W13958)
Ending Date Dec. 31, 1990 Meteorological File from Austin, TX (W13958)
Pan Evaporation Factor (PFAC) 0.69 PRZM Manual Figure 5.1 (EPA 1998).
Snowmelt Factor (SFAC) 0.36 PRZM Manual, Table 5.1 (EPA 1998).
Minimum Depth of Evaporation (ANETD) 25Mid point of range (20-30), PRZM Manual, Figure 5.2 (EPA 1998).

Table 2.
PRZM 3.12 Erosion and Landscape Parameters for Barton Springs - residential.
ParameterValue Source/Comments
Method to Calculate Erosion (ERFLAG) 4 (MUSS) Default value.
USLE K Factor (USLEK) 0.37 tons EI-1* NRCS Soil Data Mart Database for Brackett-Rock outcrop-complex, 1-12% slopes, Travis County, TX. (http://soildatamart.nrcs.usda.gov/ Exit EPA Disclaimer).
USLE LS Factor (USLELS) 1.34 Calculated according to Haan and Barfield (1978) equation: LS = ((λ/72.6)m)((430x2 + 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 (USLEP) 1 No contour plowing is expected (EPA 2004).
Field Area (AFIELD) 10 haDefault value for standard ecological pond (EPA, 2004).
NRCS Hyetograph (IREG) 4PRZM Manual, Figure 5.12 (EPA, 1998).
Slope (SLP) 6 %Brackett-Rock Outcrop-Complex slope range 1-12% (USDA 2006).
Hydraulic Length (HL) 356 mDefault value for standard ecological pond (EPA, 2004)
Irrigation Flag (IRFLAG) 1 Homeowners irrigate year round.
Kathy Shay, Water Quality Education Manager, City of Austin Watershed Protection and Development Review Board, (512-974-2446).
Irrigation Type (IRTYP) 3 (sprinkler) Kathy Shay, City of Austin; and Irrigation Guidance for developing PRZM Scenarios, Table 3; (EPA 2005).
Leaching Factor (FLEACH) 0.1 Irrigation Guidance for developing PRZM Scenario, Table 3; (June 15, 2005).
Fraction of Water Capacity when Irrigation is Applied (PCDEPL) 0.95 Irrigation Guidance for developing PRZM Scenario, Table 3; (EPA 2005). BSS homeowners typically irrigate 3 days/week, regardless of available water capacity.
Maximum Rate at which Irrigation is Applied (RATEAP) 0.032 cm hr-1 Homeowners in the BSS typically apply about twice as much as the recommended 3/4 inch of water every five days. 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.
ParameterValue Source/Comments
Initial Crop (INICRP) 1 Default value
Initial Surface Condition (ISCOND) 2 2 = cover crop. Cover crops are typically planted in residential areas 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).
Number of Different Crops (NDC) 1 Set to number of crops in simulation. Default value.
Number of Cropping Periods (NCPDS) 30Set to weather data in meteorological file: Austin, TX (W13958).
Maximum rainfall interception storage of crop (CINTCP) 0.15 Expected to be in the range of highly managed turf (0.10 as cited in PA turf and FL turf scenarios) and non-managed grasses (0.20 as cited in Dunne and Leopold, 1978).
Maximum Active Root Depth (AMXDR) 15 cm Based on managed turf grasses (Nick Smithamn, Superintendent of Austin Municipal Golf Courses, Date: 3-16-06, Phone: 512-447-2616)
Maximum Canopy Coverage (COVMAX) 100%Assumes complete turf grass coverage for lawns.
Soil Surface Condition After Harvest (ICNAH) 2 2 = cover crop. Cover crops are typically planted in residential areas 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 Emergence
(EMD, EMM, IYREM)
1/1/1961 The average first and last frost dates of the winter season are November 10 and March 10, respectively (Karen Stewart, Senior Water Conservation 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 Maturity
(MAD, MAM, IYRMAT)
1/2/1961
Date of Crop Harvest
(HAD, HAM, IYRHAR)
31/12/1961
Maximum Dry Weight (WFMAX) 0.0 Not used in scenario.
Maximum Canopy Height (HTMAX) 7.6 cm Karen Stewart, City of Austin Water Conservation Department, (512-974-2978).
SCS Curve Number (CN) 83, 83, 83 TR-55 (Table 2-2a). Composite CN for 1/4 acre residential lot assuming 38% average impervious area. Assumes year round turf (lawn) coverage with pervious curve number = 74. (USDA, 1986).
Manning's N Value (MNGN) 0.110 San Antonio Hay/Grass (I93HGHGC). Represents cover code 2 for first year hay/grass, moderately dense cover.
USLE C Factor (USLEC) 0.000 - 0.004 San Antonio Hay/Grass (I93HGHGC)

Table 4.
PRZM 3.12 "Brackett-Rock Outcrop-Complex" Soil Parameters for Barton Springs, TX - residential.
ParameterValue Source/Comments
Total Soil Depth (CORED) 48 cm Brackett-Rock outcrop-complex, 1-12% slopes, Travis County, TX. NRCS Soil Data Mart Database ( http://soildatamart.nrcs.usda.gov/ Exit EPA Disclaimer).

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.
Number of Horizons (NHORIZ) 4 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 5th HORIZN. However, these were not included in this soil profile since the 5th HORIZN is composed of bedrock.
Horizon Thickness (THKNS)
  • 2 cm (HORIZN =1)
  • 10 cm (HORIZN =2)
  • 5 cm (HORIZN =3)
  • 31 cm (HORIZN =4)
Bulk Density (BD)
  • 0.37 g/cm3 (HORIZN = 1)
  • 1.4 g/cm3 (HORIZN =2)
  • 1.4 g/cm3 (HORIZN =3)
  • 1.43 g/cm3 (HORIZN =4)
Initial Water Content (THETO)
  • 0.47 cm3/cm3 (HORIZN =1)
  • 0.28 cm3/cm3 (HORIZN =2)
  • 0.28 cm3/cm3 (HORIZN =3)
  • 0.252 cm3/cm3 (HORIZN =4)
Compartment Thickness (DPN)
  • 0.1 cm (HORIZN = 1)
  • 5 cm (HORIZN = 2)
  • 5 cm (HORIZN = 3)
  • 1 cm (HORIZN = 4)
PRZM Scenario Guidance (2004).
Field Capacity (THEFC)
  • 0.47 cm3/cm3 (HORIZN =1)
  • 0.28 cm3/cm3 (HORIZN =2)
  • 0.28 cm3/cm3 (HORIZN =3)
  • 0.252 cm3/cm3 (HORIZN =4)
Wilting Point (THEWP)
  • 0.27 cm3/cm3 (HORIZN =1)
  • 0.164 cm3/cm3 (HORIZN =2)
  • 0.164 cm3/cm3 (HORIZN =3)
  • 0.145 cm3/cm3 (HORIZN =4)
Organic Carbon Content (OC)
  • 7.5 % (HORIZN = 1)
  • 1.16 % (HORIZN =2)
  • 1.16 % (HORIZN =3)
  • 0.73 % (HORIZN =4)
Adjusted using the relationship % OC = % Organic Matter/1.724 (Doucette 2000).

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.
SoilTotal Acreage% Area Drainage ClassKFSlope pHOM (%)Sand (%) Silt (%) Clay (%)
Brackett 10,044 34.8% C 0.37 1 - 12 82 34 38 28
Tarrant 3,322 11.5% D 0.32 5 - 18 85 22 28 50
Speck 2,594 9.0% D 0.32 1 - 3 72 34 37 30
Real 1,891 6.6% D 0.28 1 - 8 86 36 34 31
Comfort 1,869 6.5% D 0.32 1 - 8 86 28 29 43
Urban land 1,269 4.4% D 0.00 0 - 6 00 0 0 0
Rumple 1,120 3.9% C 0.32 1 - 8 72 34 37 30
Eddy 959 3.3% C 0.32 1 - 3 81 38 36 26
Volente 832 2.9% C 0.321 - 88 3 7 54 39
Doss 819 2.8% D 0.321 - 58 2 7 49 44
Denton 544 1.9% D 0.321 - 38 3 6 48 46
Purves 448 1.6% D 0.321 - 58 3 23 29 48
Crawford 357 1.2% D 0.320 - 17 2 22 28 50
Austin 343 1.2% C 0.321 - 38 3 7 48 45
Krum 315 1.1% D 0.320 - 18 2 26 29 45
Houston Black 308 1.1% D 0.321 - 38 3 17 28 55
San Saba 307 1.1% D 0.321 - 28 3 18 29 53
Heiden 188 0.7% D 0.321 - 38 3 22 28 50
Bolar 173 0.6% C 0.321 - 38 2 34 37 30
Sunev 163 0.6% B 0.320 - 18 2 18 52 30
Medlin 159 0.5% D 0.321 - 88 2 22 28 50
Tarpley 149 0.5% D 0.321 - 37 3 30 30 40
Castephen 130 0.4% C 0.323 - 58 2 34 32 34
Lewisville 117 0.4% B 0.320 - 18 2 8 51 41
Anhalt 94 0.3% D 0.32 1 - 3 73 26 29 45
Alluvial land 87 0.3% A 0.15 0 - 1 81 90 0 5
Patrick 85 0.3% B 0.32 2 - 5 82 28 29 43
Gruene 59 0.2% D 0.28 1 - 5 82 28 29 43
Eckrant 28 0.1% D 0.32 8 - 40 87 22 28 50
Ferris 26 0.1% D 0.32 8 - 20 81 18 29 53
Orif 17 0.1% A 0.28 0 - 1 82 82 9 9
Altoga 16 0.1% C 0.32 3 - 6 81 7 48 45
Oakalla 10 0.0% B 0.32 0 - 1 84 18 48 34
Seawillow 9 0.0% B 0.32 1 - 3 81 35 34 31
Tinn 6 0.0% D 0.32 0 - 1 83 22 28 50
Travis 3 0.0% C 0.24 1 - 8 71 66 19 15
Hardeman 3 0.0% B 0.24 3 - 12 81 66 20 14
Whitewright 2 0.0% C 0.32 1 - 5 81 31 33 37
Gaddy 2 0.0% A 0.17 0 - 1 80 84 7 10
Bergstrom 1 0.0% B 0.32 0 - 2 82 7 62 31
Boerne 0 0.0% B 0.28 1 - 3 81 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

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

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/. Exit EPA Disclaimer

Dunne, T., and L. Leopold. 1978. Water in Environmental Planning. W.H. Freeman an Company, New York. 818 pp.

EPA. 1998. Carsel, R.F., J.C. Imhoff, P.R. Hummel, J.M. Cheplick, and A.S. Donigian, Jr. PRZM-3, A Model for Predicting Pesticide and Nitrogen Fate in the Crop Root and Unsaturated Soil Zones: Users Manual for Release 3.0. National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA.

EPA. 2004. Pesticide Root Zone Model (PRZM) Field and Orchard Crop Scenarios: Guidance for Selecting Field Crop and Orchard Scenario Input Parameters. November 15, 2001; Revisions July 2004.

EPA. 2005. Irrigation Guidance for developing PRZM Scenario. June 15, 2005.

Haan, C.T. and B.J. Barfield. 1978. Hydrology and Sedimentology of Surface Mined Lands. Office of Continuing Education and Extension, College of Engineering, University of Kentucky, Lexington, Kentucky 40506. pp. 286.

Perez, C. 2006. NRCS - District Conservationist. Personal communication. March 17 & 20, 2006.

Robinson, R. 2006. City of Austin, Watershed Protection and Development Review Dept., Stormwater Quality Monitoring Program. Phone: 512-974-2394. Personal Communication (March 2006).

Shay, K. 2006. City of Austin, Watershed Protection and Development Review Board, Personal communication, March 16, 2006.

Soil Survey Staff, Natural Resources Conservation Service, United States Department of Agriculture. Official Soil Series Descriptions [Online WWW]. Available URL: http://soils.usda.gov/technical/classification/osd/index.html Exit EPA Disclaimer [Accessed 6 March 2006].

Stewart, K. 2006. City of Austin, Water Conservation Department (512-974-2978), Personal communication, March 22, 2006.

USDA. 2000. Revised Universal Soil Loss Equation (RUSLE) EPA Pesticide Project. U.S. Department of Agriculture, National Resources Conservation Service (NRCS) and Agricultural Research Service (ARS).

USDA. 2001. Official Series Description. Brackett Series. Information from the website: https://soilseries.sc.egov.usda.gov/OSD_Docs/B/BRACKETT.html. Exit EPA Disclaimer

USDA. 2006. Soil Survey Areas of Hays Counties, Texas. U.S. Department of Agriculture, Natural Resources Conservation Service (NRCS), Soil Data Mart. March 1, 2006. Online at: http://soildatamart.nrcs.usda.gov. Exit EPA Disclaimer

USGS, National Mapping Division, Rocky Mountain Mapping Center. 2003. Edwards Aquifer Land Use / Land Cover. Denver, Colorado.

Volente, Village of. 2004. Comprehensive Plan, village of Volente, Texas. Draft Report.


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