Agua Hedionda Watershed Management Plan

1. Agua Hedionda Watershed Management Plan Watershed Planning Group Meeting March 27, 2008 Carlsbad, CA

2. Agenda Preliminary Modeling ResultsLID Constraints and Conceptual DesignsEvaluation Process for Identifying Acquisition, Restoration, and BMP Retrofit OpportunitiesFinalizing Goals and Objectives

3. Preliminary Modeling Results

4. Modeling Objectives • Represent watershed hydrology and pollutant loading • Assess hydromodification and water quality • Simulate various development scenarios

5. Model Scenarios • Existing Condition (based on 2007 SANDAG land use) • Predevelopment Condition (all development converted to open space) • Future Condition (based on 2030 SANDAG land use) • Representation of lawn irrigation and BMP treatment has been incorporated

6. LSPC Model • LSPC is the Loading Simulation Program in C++, developed by the U.S. Environmental Protection Agency (EPA) Region 4, with support of Tt • Watershed modeling system includes streamlined HSPF algorithms for simulating hydrology, sediment, and general water quality on land and in stream • Used to represent the build up, wash off, and first order decay processes of pollutants and sediment processes (on land and in channel)

7. Hydrologic Components: Precipitation Interception Evapotranspiration Overland flow Infiltration Interflow Subsurface storage Groundwater flow Groundwater loss Hydrology Schematic of Stanford Watershed Model

8. Model Inputs • Land use data from SANDAG; modified using parcel data for finer resolution of residential categories; future land use modified based on feedback from municipalities • Precipitation from Oceanside Pumping Plant; PET from a variety of CIMIS stations • Model subwatersheds delineated from 10m DEM; stream characteristics based on drainage area:width/depth relationships • Demand-based lawn irrigation

12. Model Parameters • Initial basis for parameterization: • Hydrology: San Diego Region TMDL Model and other SoCal model applications • Bacteria: San Diego Region TMDL Model (Bacti-II Draft) • Nutrients: San Jacinto model • Sediment: SCCWRP regional sediment approach • Local watershed properties • Some parameters adjusted during calibration

13. Model Calibration • Began with regionally calibrated model (to flow and bacteria) • Some additional but limited local calibration was possible • ~1 year of stream flow data (2005-2006) • Wet weather water quality data at one station (El Camino Real Bridge): 1998 – 2006 (25 observations)

14. Mean Daily Flow Model Outlet 1007 vs. Agua Hedionda Creek At El Camino Real Bridge

15. Seasonal Regression and Temporal Aggregate Model Outlet 1007 vs. Agua Hedionda Creek At El Camino Real Bridge

20. BMP Representation • Two general types of BMPs represented in the model • Hydrologic Source Control (HSC) • Storm Water Treatment (SWT) • HSC reduces runoff volumes and rates primarily through infiltration • Examples may include vegetated swales*, biofilters, infiltration basins, permeable pavement, media filters • SWT removes pollutants after they have entered concentrated flow paths • Examples may include extended dry detention*, constructed wetlands, wet ponds, hydrodynamic devices, catch basins * Most common in Agua Hedionda

21. Interpretation of SW Requirements • Existing treatment was determined through a review SUSMP BMPs and from information provided by Carlsbad on older detention ponds • SDRWQB Order 2001-01: requires water quality treatment for priority projects (either volume- or flow-based wq treatment) • Future priority projects must meet Order 2001-01 plus the 2007 Order • Peak flow control for continuous range of storms (channel protection-based requirement) • LID practices (level of requirement unclear) • Assumed that Priority Projects receive treatment in all future development except for Very Low Density (>1ac) and approximately half of Low Density (0.5-1.0ac)

22. ToSWT2 ToHSC1 ToSWT1 ToStream Existing Scenario Infiltration goes to nearby urban pervious baseflow Impervious 55% 10% 5% 30% Untreated Overflow 40% 5% 55% Hydrologic Source Control Untreated Bypass Untreated Bypass StormwaterTreatment 1 StormwaterTreatment 2 Effluent Conc. Effluent Conc. Drainage Areaboxes represent a mix of land use. Stream Segment

23. Future Scenario Infiltration goes to nearby urban pervious baseflow Impervious Variable % Variable % ToHSC1 ToSWT3 + “Existing” Configuration 100% Overflow Hydrologic Source Control Untreated Bypass StormwaterTreatment 3 Effluent Conc. Drainage Area boxes represent different land uses developed in the future. Stream Segment Moderate levels of LID application applied in the form of 4-10% impervious reduction.

24. Three Scenarios • Predevelopment • Existing Condition • Future Conditions w/ BMPs • Future Conditions w/o BMPs

25. Storm Hydrograph 2/12/2001 - 2/14/2001

26. Sediment Loading at Lagoon

27. Next Steps • Integrate with geomorphic analysis • Final QA/QC, generate additional model output, and develop model report • Use model output to target and re-prioritize management recommendations in the WMP (e.g., priority subwatersheds, evaluate loading to lagoon, etc)

28. LID Constraints and Conceptual Designs

29. Future Developmentby Planned Land Use Future Developmentby Planned Land Use

30. Constraints - Slope • As slopes increase, many LID techniques become more difficult to implement • 0% to 15% - Low • 15% to 25% - Medium • >25% - High (hillslope development)

31. Constraints - Slope • For the majority of developing areas, slope is a low to medium constraint • Many high slopes in areas planned for Very Low Density Residential.

32. Constraints - Slope Constraints - Slope

33. Constraints – Soil Erosion Hazard • Soil erosion hazard estimated to be mostly slight to moderate • Correlated to slope • Some localized hotspots

34. Constraints – Soil Erosion Hazard Constraints – Soil Erosion Hazard

35. Constraints – Soil Infiltration • In most of the developing area, infiltration rates are very low • In upper watershed, rates are better but still low

36. Constraints – Soil Infiltration • Low and very low infiltration rates produce the biggest physical constraint to many important LID practices • Not feasible • Dry wells/infiltration basins • More costly to implement (need underdrains) • Bioretention • Permeable asphalt/concrete

37. Constraints – Soil Erosion Hazard Constraints – Soil Infiltration

38. Other Constraints • Arid conditions/low rainfall • Constraint for BMPs with permanent pools (wet ponds) • Not a constraint for vegetation in BMPs, which can be maintained with irrigation/sprinklers

39. Conceptual Designs • Very low density residential in high sloped areas • Not regulated as Priority Projects • Best practice: Cluster development avoiding high slopes and riparian areas • Shared driveways and tucked-under parking • Permeable pavers for sidewalks/patios • Cisterns used to supplement irrigation

40. Conceptual Designs • Single Family Residential • Avoid higher sloped/more erosive areas • Riparian buffer setbacks • Vegetated or rock-lined swales • Extended Dry Detention Basins • Shared driveways and tucked-under parking • Permeable pavers for sidewalks/patios • Cisterns used to supplement irrigation

41. Conceptual Designs • High density mixed-use areas (commercial/multifamily) • Vegetated or rock-lined swales • Extended Dry Detention Basins • Bioretention (with underdrains) • Turf block fire lanes • Roof drains diverted to large flat pervious areas • Cisterns used to supplement irrigation (can be large and incorporated into building design)

42. Conceptual Designs • Warehouse/industrial • Vegetated or rock-lined swales • Extended Dry Detention Basins • Turf block fire lanes • Roof drains diverted to large flat pervious areas • Cisterns used to supplement irrigation (can be large and incorporated into building design)

43. Evaluation Process for Identifying Acquisition, Restoration, and BMP Retrofit Opportunities

44. Land Acquisition and Restoration • Identifying opportunities for • Land Acquisition for Preservation • Buffer Restoration • Wetlands Restoration • Prioritizing opportunities based on Goal #2 • Considering Goal #3 in relation to water quality benefits

45. Goal #2 and Objectives • Protect , restore and enhance habitat in the watershed. • Protect and expand undeveloped natural areas to protect habitat. • Protect, enhance, and restore terrestrial habitat, especially existing vegetation in riparian areas. • Provide riparian habitat to improve and maintain wildlife habitat. • Provide natural area connectivity to improve and maintain wildlife habitat. • Maintain stable stream banks and riparian areas to protect instream aquatic habitat and priority tree species. • Maintain and protect instream habitat to support native aquatic biology. • Maintain and protect lagoon habitat.

46. Goal #3 • Restore watershed functions, including hydrology, water quality, and habitat, using a balanced approach that minimizes negative impacts.

47. Approach • Identify subwatersheds with highest quality natural areas and wildlife habitat  “Priority Subwatersheds” • Prioritize preservation and restoration opportunities by • Priority Subwatersheds • Screening criteria that measure likelihood of achieving Goal #2 and providing water quality benefits

48. Priority Subwatershed Screening Criteria • Natural Areas – naturally vegetated areas • Terrestrial Habitat – natural areas and undeveloped, disturbed land that provide wildlife habitat (e.g., agriculture) • Riparian Habitat – land that supports riparian vegetation • CRAM – Ratings of wetland function. • Aquatic Habitat Rating – Qualitative ratings from field reconnaissance. • MSCP/MHCP Priority Species Observations • Lagoon/Coastal Subwatersheds – Used to further prioritize lagoon and coastal habitat. • Soil Erosion Hazard – Rated by NRCS index as having severe or very severe erosion hazard

49. Comparison to MHCP and MSCP • Multiple Habitat and Species Conservation Plans (MHCP and MSCP) • Checked that connectivity provided between: • MHCP/MSCP planning, core, and linkage areas • AH priority subwatersheds

50. Land Acquisition Screening Criteria • Location within a Priority Subwatershed • Unprotected Natural Areas – naturally vegetated areas that may be developed in the future. • Riparian Habitat – land that supports riparian vegetation. • Location Relative to a Stream Restoration Opportunity • Location relative to invasive species treatment areas • Soil Erosion Hazard – land rated by NRCS index as having severe or very severe erosion hazard.  Used to prioritize parcels for preservation