The Potential for Beneficial Use The Potential for Beneficial Use of Stormwater Stormwater in Pima County in Pima County of Findings of the City/County Findings of the City/County Study on the Use of Stormwater Stormwater Study on the Use of Evan Canfield PhD, PE Evan Canfield PhD, PE Dave Stewart EIT Dave Stewart EIT Pima County Regional Flood Control Pima County Regional Flood Control District District
‘Harvestable Harvestable’ ’ Water Water ‘ (Rainwater/Stormwater Stormwater) ) (Rainwater/ 100% Neighborhood Tributary Regional Lot Scale Scale Watercourse Watercourse (< 2 ac) 90% 2 to ~100 mi 2 ) 2 ) (2 ac to 64 ac) (0.1 mi (> ~100 mi 80% Harvestable Stormwater 70% WRRC Data USGS Gage 60% y = 0.0734e -0.5845 log (A) USDA ARS Data R 2 = 0.90 Model Developed 50% Model Undeveloped 40% Regression for Developed y = 0.0334e -0.3366 log (A) Regression for Undeveloped 30% R 2 = 0.85 20% 10% 0% 0.000001 0.00001 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 Area (sq mi)
Mean Monthly Rainfall Tucson Airport Mean Monthly Rainfall Tucson Airport (Western Regional Climatic Center) (Western Regional Climatic Center) 3 2.5 1996-2008 1961-1990 Mean Monthly Rainfall (inches) 2 1.5 1 0.5 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Tree Water Use Tree Water Use
Annual Estimate of Plant Water Use Annual Estimate of Plant Water Use � Annual Water Requirement Annual Water Requirement � � City of Tucson City of Tucson – – Water Harvesting Water Harvesting � Development Standard Development Standard • Velvet Mesquite (30 Velvet Mesquite (30’ ’ canopy) canopy) – – 9,000 gal/yr 9,000 gal/yr • • Low Water Use Plant Low Water Use Plant – – 20.2 inches/yr 20.2 inches/yr • � Orange Tree (Wright, U of A Extension 2000) Orange Tree (Wright, U of A Extension 2000) � • 20 20’ ’ Canopy Canopy - - 11,300 gal/yr 11,300 gal/yr • • 30 30’ ’ Canopy Canopy – – 25,500 gal/yr 25,500 gal/yr •
Active Rainwater Harvesting Active Rainwater Harvesting
Root Zone Storage Root Zone Storage Caliche
Water Volume in Tree Root Zone Water Volume in Tree Root Zone (3' root depth) (3' root depth) 8000 7000 Saturation - Sandy Soils (42%) Saturation - Loamy Soils (44%) 6000 Available Water - Sandy Soils (8%) Volume in Root Zone Available Water - Loamy Soils (16%) 5000 (gallons) 4000 3000 2000 1000 0 0 5 10 15 20 25 30 Tree Diameter (feet)
Lot Scale Evaluation Lot Scale Evaluation (1/5 acre lot example) (1/5 acre lot example) Right of Evaluate Effectiveness of Water Harvesting Features Way Directly Connected Impervious Area Pervious R Area o a Water Harvesting Basin d w Lot a Width y Unconnected Impervious Area Directly Connected Impervious Area Length
Conceptual Model Conceptual Model Conceptual Representation Mathematical Representation − 2 ( P 0 . 2 S ) = Q + ( P 0 . 8 S ) Q is the total depth of runoff (inches); P is the daily rainfall depth of precipitation (inches); S is the potential abstraction (inches) Unconnected Impervious Area (UA) 1000 − Directly Connected Impervious Area = CN S 10 Pervious Area (PA) CN is the Curve Number. Rainwater off lot from Directly Connected: = Vol Q ( f ( CN P )] xArea ( ) , DCA i i DCA i DCA Rainwater in to Water Harvesting Basin: = ( ( )] Vol Q f CN P xArea ( UA ) i i UA , i UA = ( ( )] Vol Q f CN P xArea ( PA ) i i PA , i PA (DCA) Storage Accounting in Basin: = − + Δ Storage ( i ) Storage ( i 1 ) Storage Water Harvesting Basin Δ = i − Storage Rainwater ET i (ETo AZmet * Kc)
Data Sets Data Sets � Daily Rainfall Data Daily Rainfall Data – – 108 years of data 108 years of data � gathered at U of A. gathered at U of A. � Mean Daily Reference ET ( Mean Daily Reference ET (ETo ETo) ) – – from from � Campbell Avenue Farm Campbell Avenue Farm Penman Monteith ETo (in/day) 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 0-Jan 30-Jan 29- 30- 29- 29- 28-Jun 28-Jul 27- 26- 26-Oct 25- 25- Feb Mar Apr May Aug Sep Nov Dec Day of Year
Supplemental Water Supplied, and Supplemental Water Supplied, and Harvested Stormwater Stormwater from a from a Lotside Lotside Swale Swale Harvested on a 1/5 acre lot on a 1/5 acre lot 50 Supplemental Water Range of Supplemental Water Required Provided 45 Stormwater 40 Harvested 35 Number of Years 30 25 20 15 10 5 0 9 9 9 9 9 9 9 9 9 9 9 0 9 9 9 9 9 9 9 9 9 9 9 0 1 3 5 7 9 1 3 5 7 9 1 2 1 1 1 1 1 2 2 < - - - - 0 0 0 0 - - - - - - > 0 0 0 0 0 0 0 0 0 0 2 4 6 8 0 0 0 0 0 0 0 2 4 6 8 0 1 1 1 1 1 2 Annual Volume (cubic ft)
Modeled Mesquite Water Requirements (ET) and Modeled Mesquite Water Requirements (ET) and Water Harvested in a Lotside Lotside Swale on a 1/5 Swale on a 1/5 Water Harvested in a acre- -lot lot acre 5.00 Stormwater 4.50 Harvested ET 4.00 3.50 Average Depth (in) 3.00 2.50 2.00 1.50 1.00 0.50 0.00 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month
Supplemental Water Supplied, and Supplemental Water Supplied, and Harvested Stormwater Stormwater from a from a Lotside Lotside Swale Swale Harvested on a 1/5 acre lot on a 1/5 acre lot 50 Supplemental Water Range of Supplemental Water Required Provided 45 Stormwater 40 Harvested 35 Number of Years 30 25 20 15 10 5 0 9 9 9 9 9 9 9 9 9 9 9 0 9 9 9 9 9 9 9 9 9 9 9 0 1 3 5 7 9 1 3 5 7 9 1 2 1 1 1 1 1 2 2 < - - - - 0 0 0 0 - - - - - - > 0 0 0 0 0 0 0 0 0 0 2 4 6 8 0 0 0 0 0 0 0 2 4 6 8 0 1 1 1 1 1 2 Annual Volume (cubic ft)
Potential Root Zone Stormwater Stormwater Potential Root Zone Storage (for illustration purposes only) Storage (for illustration purposes only) Ret Vol Ret Vol # Trees Acres #Lots (ac-ft) (gallons) (1) Tree/Lot 4.8 17 0.35 114,040 22.8 1.3 3.8 9 0.24 78,199 15.6 1.7 4.4 13 0.25 81,457 16.3 1.3 1 Assumes 30’ Velvet Mesquite with 5000 gallons potential storage in root zone
Low Impact Development (LID) Low Impact Development (LID) � LID Planning LID Planning � � Disconnect and minimize Disconnect and minimize � impervious surfaces. impervious surfaces. � Maintain pre Maintain pre- -development development � waterways. waterways. � LID Flow Paths LID Flow Paths � � Lengthen and roughen Lengthen and roughen � overland flow paths. overland flow paths. � LID Infiltration/ Features LID Infiltration/ Features � � Pervious pavement. Pervious pavement. � � Swales, filter strips. Swales, filter strips. � � Bioretention Bioretention. . � � Rainwater catchment Rainwater catchment � systems. systems. � Detention basins. Detention basins. � Source: Low Impact Development Center
Stormwater Quality BMPS in Practice Quality BMPS in Practice Stormwater at Rincon Heights Neighborhood at Rincon Heights Neighborhood Photo: Watershed Management Group (WMG)
Native Vegetation Irrigated with Harvested Native Vegetation Irrigated with Harvested Stormwater at Highland Vista Park at Highland Vista Park Stormwater
Stormwater Harvesting at Harvesting at Stormwater KERP KERP
Water Demand and Harvested Water Demand and Harvested Stormwater at KERP at KERP Stormwater 2004 2005 2006 2007 2007 2008 2008 2004 2005 2006 Demand Demand (in acre- -feet) feet) 582 582 582 582 582 (in acre 582 582 582 582 582 Reclaimed Water 330 180 395 160 188 Reclaimed Water 330 180 395 160 188 Harvested Water 252 402 187 422 394 Harvested Water 252 402 187 422 394 Annual Rainfall Annual Rainfall (in inches) 7.60 9.57 11.81 11.81 9.78 8.67 (in inches) 7.60 9.57 9.78 8.67
Summary Summary � The City/County The City/County stormwater stormwater study found that the study found that the � greatest potential for beneficial use of greatest potential for beneficial use of stormwater was at the lot and neighborhood was at the lot and neighborhood stormwater scales . . scales � Storage is the greatest limiting factor Storage is the greatest limiting factor in in � beneficial use of stormwater stormwater. . beneficial use of � Passive Passive stormwater stormwater harvesting can be an harvesting can be an � excellent strategy to supply water requirements to supply water requirements excellent strategy for deep- -rooted drought rooted drought- -tolerant plants. tolerant plants. for deep � Stormwater Stormwater harvesting is harvesting is best evaluated in terms best evaluated in terms � of a strategy that achieves multiple benefits of a strategy that achieves multiple benefits including flood control, stormwater stormwater water quality water quality including flood control, management, habitat preservation and management, habitat preservation and mitigating urban heat island effects. mitigating urban heat island effects.
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