Investigation and Analysis Report

APPENDIX D Investigation and Analysis Report

REPORT Investigation and Analysis Report Franktown-Parker FP-B1 (Baldwin Gulch) Watershed Dam Supplemental Watershed Planning Study

Submitted to: Douglas County Engineering 100 Third Street, Castle Rock, Colorado 80111

Submitted by: Golder Associates Inc. 44 Union Boulevard, Suite 300, Lakewood, Colorado 80228

+1 303 980-0540

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Table of Contents

1.0 INTRODUCTION ...... 1

1.1 Data Compilation ...... 3

2.0 INVESTIGATION AND ANALYSIS SUMMARY ...... 3

2.1 Hydrology ...... 3

2.2 Embankment Geotechnical Stability ...... 4

2.3 Sediment Deposition ...... 4

2.4 Overall Condition Assessment ...... 5

2.5 Auxiliary Spillway Stability and Integrity ...... 5

2.6 Natural Resources Survey ...... 5

2.6.1 Wildlife ...... 5

2.6.2 Vegetation ...... 6

2.7 Cultural Resources Survey ...... 7

2.8 Air Quality/Noise ...... 7

2.9 Hazard Classification Assessment ...... 7

3.0 ALTERNATIVES ASSESSMENT ...... 7

3.1 Existing Conditions ...... 8

3.2 Design Hydrology (Inflow Design Flood Analysis) ...... 9

3.2.1 State of Colorado Methodology ...... 10

3.2.2 NRCS Methodology ...... 10

3.2.3 Auxiliary Spillway Hydrograph Analysis ...... 11

3.2.4 Design Hydrology Summary ...... 12

3.3 Design Criteria ...... 13

3.4 Preliminary Alternatives ...... 13

3.4.1 Alternative 1 – No Action/Future without Project ...... 15

3.4.2 Alternative 2 – Decommissioning ...... 16

3.4.3 Alternative 3 – Existing Auxiliary Spillway Widening ...... 17

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3.4.4 Alternative 4 – Overtopping Protection ...... 17

3.4.5 Alternative 5 – Roller Compacted Concrete (RCC) Auxiliary Spillway ...... 18

3.4.6 Alternative 6 – Hazard Reclassification through RCC Auxiliary Spillway Construction and Downstream Flood Proofing ...... 19

3.4.7 Alternative 7 – Principal Spillway Replacement and RCC Auxiliary Spillway ...... 20

3.5 Hydrologic & Hydraulic Evaluations of Alternatives ...... 20

3.6 Comparative Estimated Implementation Costs ...... 23

4.0 ECONOMIC EVALUATIONS ...... 24

4.1 Hydrology and Flooding Extents ...... 24

4.1.1 Estimation of Flooding Extents, Depths, and Velocities ...... 24

4.2 Damage Estimates ...... 25

4.2.1 Value Determinations ...... 25

4.2.2 Estimation of Damages ...... 25

4.3 Benefit-Cost Evaluations ...... 27

5.0 SUMMARY AND RECOMMENDATIONS ...... 27

6.0 REFERENCES ...... 28

TABLES (IN TEXT) Table D-1: FP-B1 Dam Characteristics ...... 1 Table D-2: Inflow Design Flood Analysis Summary ...... 4 Table D-3: Design Precipitation Depth Criteria ...... 9 Table D-4: Precipitation Depth Summary using State of Colorado Criteria ...... 10 Table D-5: Precipitation Depth Summary Using NRCS Criteria ...... 10 Table D-6: Composite Curve Number (CN) Estimate ...... 11 Table D-7: Inflow Design Flood Analysis Summary ...... 12 Table D-8: Watershed Dam FP-B1 Design Criteria for Significant & High Hazard Alternatives ...... 13 Table D-9: Watershed Dam FP-B1 Design Criteria for Significant & High Hazard Alternatives ...... 22 Table D-10: Estimated Implementation Costs ...... 23

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TABLES (AT END)

Table D-11: Evaluation Matrix

PHOTOS Photo D-1: Location Map ...... 2 Photo D-2: FP-B1 Embankment and Spillway ...... 9 Photo D-3: Decommissioning Alternative ...... 16 Photo D-4: Typical RCC Embankment Spillway ...... 19

FIGURES

Figure D1: Alternative 1-No Action Alternative

Figure D2: Alternative 2-Decommissioning

Figure D3: Alternative 3-Existing Auxiliary Spillway Widening Alternative (Significant Hazard Classification)

Figure D4: Alternative 4-RCC Overtopping Protection

Figure D5: Alternative 5-RCC Spillway (High Hazard Classification)

Figure D6: Alternative 6-RCC Spillway (Significant Hazard Classification)

Figure D7: Alternative 7-Principal Spillway Replacement & RCC Auxiliary Spillway

Figure D8: Water Surface Profiles for the 100-yr Recurrence Interval Event

Figure D9: Water Surface Profiles for the 500-yr Recurrence Interval Event

Figure D10: Water Surface Profiles for the PMP Event

Figure D11: Golder Dam Breach Inundation Extent and FEMA 100-year Floodplain

Figure D12: 100-year Floodplain Extents with and without Dam

Figure D13: 100-year Storm Event Dam/No Dam Water Surface Profiles

Figure D14: 500-year Storm Event Dam/No Dam Water Surface Profiles

Figure D15: 500-year Floodplain Extents Existing and Proposed Rehabilitation Alternative

Figure D16: Estimated Benefits per Event

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ATTACHMENTS ATTACHMENT D-1 Alternatives Cost Estimate Summary ATTACHMENT D-2 Summary of Damage Estimates ATTACHMENT D-3 Computation of Population at Risk (PAR)

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1.0 INTRODUCTION This Investigation and Analysis (I&A) report summarizes the investigations, studies and evaluations conducted to support the formulation, evaluation and conclusions contained in the Supplemental Environmental Assessment Watershed Planning Study (PLAN-EA) for the Franktown-Parker FP-B1 (Baldwin Gulch) Watershed Dam (NID ID: CO056129). The watershed plan supplement is being developed to evaluate alternatives to bring the dam into compliance with current Natural Resources Conservation Service (NRCS) and State of Colorado performance and dam safety standards.

The dam is a flood control structure located east of Parker, Colorado on Baldwin Gulch, which is a tributary to Cherry Creek. It is located in Section 14, Township 6 South, Range 66 West of the 6th Principal Meridian, in Douglas County, Colorado. The dam is operated and maintained by Douglas County and the Douglas County Conservation District. The dam was constructed as a flood control facility to alleviate the potential for flooding in downstream areas, including residential and commercial structures, and roadways within Baldwin Gulch. The dam was also constructed as part of a system of flood control facilities to alleviate the overall flooding potential within Cherry Creek. If the dam is not modified to meet current State and Federal dam safety requirements, it is likely that the dam would need to be decommissioned and the flood control benefit associated with the facility would be lost. The benefit associated with implementing dam safety improvements to the dam is the reduction in damages associated with keeping the dam in service.

Table D-1 provides a summary of the characteristics of the dam and Photo D-1 provides an overview of the general dam location.

Table D-1: FP-B1 Dam Characteristics Variable Value

Embankment

Crest Elevation (feet NAVD88)1 5,963.6

Length (feet)1 1,500

Maximum Height (feet)1 22

Crest Width (feet)1 13

Embankment Side Slopes (XH:1V)1 2½H:1V

Storage Volume to Auxiliary Spillway Crest (acre-feet)1 148.1

Storage Volume to Dam Crest (acre-feet)1 250.9

Primary Spillway

Type Drop Inlet

Crest Elevation (feet NAVD88)1 5,952.0

Capacity (cfs)2 46.9

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Variable Value

Emergency (Auxiliary) Spillway

Type Vegetated

Crest Elevation (feet NAVD88)1 5,959.4

Freeboard (feet)1 4.2

Width (feet)1 100

Capacity (cfs)2 1,680

Hydrology

Watershed Areas (square miles)1 2.27 Notes: 1) Structural data obtained from 2009 topographic survey conducted by Landmark Mapping, Ltd and provided by Urban Drainage and Flood Control District. 2) Structural data adopted from as-built documentation of the dam (NRCS 1960) adjusted to North American Vertical Datum of 1988 (NAVD1988).

Photo D-1: Location Map

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1.1 Data Compilation Some existing information and data exists for the FP-B1 (Baldwin Gulch) Dam. A list of the available documents that were provided by Douglas County and the NRCS are provided below:  Franktown-Parker Tributaries of Cherry Creek Watershed Work Plan (1960)  As-built Drawings for Detention Dam FP-B1 (1963)  Additional Design Documentation including hydrologic studies, geotechnical investigations and correspondence from NRCS and Colorado DWR files  Flood Hazard Area Delineation: Happy Canyon Creek, Badger Gulch, Newlin Gulch, Baldwin Gulch, Sulphur Gulch, Tallman Gulch (HNTB 1977)  State of Colorado Engineer’s Inspection Reports (1976, 1979, 1988, 1994, 2000, 2006, 2016)  Newlin and Baldwin Gulches and Basin 4600-09 Outfall Systems Planning Study Preliminary Design Report (Kiowa, 1994)  Phase 2 Baldwin Gulch Floodplain Modifications As-constructed Drawings (Carter, 2003)  Franktown Parker – B1 Dam on Baldwin Gulch Hazard Classification Report (Muller Engineering, 2014)  Flood Insurance Study, Douglas County, Colorado and Incorporated Areas. Flood Insurance Study No. 08035CV001A (FEMA, 2005)  Road Closure Evaluation, Technical Memorandum. December 3, 2018 (Douglas County Engineering, 2018) 2.0 INVESTIGATION AND ANALYSIS SUMMARY The existing design and condition of the FP-B1 dam was evaluated as part of developing the Investigation and Analysis Report. This review was based on a site reconnaissance and review of the existing information for the dam and associated components. 2.1 Hydrology A hydrologic evaluation was undertaken by Wilson and Company to estimate peak discharge rates for the Probable Maximum Precipitation (PMP) event and the “sunny day” dam failure scenario for the existing facility (Wilson 2016). The hydrology was updated as part of evaluating alternatives for the facility. The peak Inflow Design Flood (IDF) used for evaluations and alternatives assessment are summarized in Table D-2 below:

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Table D-2: Inflow Design Flood Analysis Summary Precipitation Peak Depth Inflow Storm Event (in) (cfs) Standard

High Hazard

FBH – 100% PMP1 33.73 8061 NRCS-Auxiliary spillway integrity

IDF-90% General Storm2 – USBR 30.35 16771 Colorado DWR-Spillway capacity

1 ASH-P100 +0.26 (PMP-P100) 12.26 2525 NRCS-Auxiliary spillway stability

Significant Hazard

1 FBH – P100 +0.40 (PMP-P100) 16.32 3592 NRCS-Auxiliary spillway integrity

IDF-45% General Storm2 – USBR 15.18 7830 Colorado DWR-Spillway capacity

1 ASH-P100 + 0.12 (PMP-P100) 8.19 1477 NRCS-Auxiliary spillway stability

100-year/24-hour3 4.71 1730 Colorado DWR & NRCS

500-year/24 hour3 6.12 2574 Colorado DWR & NRCS Notes: 1) Table 2-5 in TR-60. Distributed using dimensionless design storm distribution in Figure 2-4. (NRCS 2005). 2) General storm distribution based on methods detailed in Section 3.4 of the Bureau of Reclamation, Flood Hydrology Manual. 3) SCS Type 2 Distribution.

Based on the evaluations undertaken, the General Storm with USBR distribution based on the State of Colorado criteria generated higher peak discharges for both the Significant and High Hazard classifications. As such, those peak discharges and hydrologic models were used to size and evaluate the various alternatives. 2.2 Embankment Geotechnical Stability The stability of the existing FP-B1 dam was assessed in accordance with the Rules and Regulations for Dam Safety and Dam Construction set forth by the State of Colorado Department of Natural Resources, Division of Water Resources, Office of the State Engineer, Dam Safety Branch (State of Colorado 2007) and Earth Dams and Reservoirs (TR-60) (NRCS 2005). Stability was evaluated for steady seepage with phreatic surface fully developed for reservoir at spillway crest elevation, rapid drawdown (upstream slope), and seismic (pseudo-static) conditions. Stability was analyzed for the maximum cross-section for the dam, as presented on the As-Built Drawings. Material properties were developed using existing laboratory test results from the late 1970s, documents provided by NRCS, previous stability analyses for the dams, and engineering judgment where measured or previously specified properties were unavailable. The stability analyses conducted for the as-built configuration of the existing FP-B1 dam indicates that the factors of safety are acceptable in accordance with current State of Colorado and NRCS Rules and Regulations. (Golder 2018a). 2.3 Sediment Deposition The historic sediment deposition in the reservoir impoundment was evaluated based on comparison of historical and more recent topographic data within the reservoir inundation area (Wilson 2016). As this reservoir has not seen large volumes of water stored for long periods of time, the amount of sediment deposition is assumed to be

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minimal. A site reconnaissance of the reservoir pools indicates that minimal sediment has accumulated. This is supported by comparing topographic data following construction with more recent (2014) topographic data. Based on minimal sediment deposition in the reservoir, the useful life of the facility is assumed to be 100 years. 2.4 Overall Condition Assessment The last inspections conducted by the State of Colorado Division of Water Resources indicated no major concerns with the existing outlet works, primary and auxiliary spillways. The existing principal spillway structure and drawdown inlet components appear to be in good condition. However, the principal spillway pipe could not be examined. A more thorough condition assessment was conducted as part of preparing the PLAN-EA (Wilson 2016a). These investigations concluded that the hydraulic structures associated with the FP-B1 dam are generally in good condition and not in need of immediate repair or replacement. 2.5 Auxiliary Spillway Stability and Integrity The Water Resources Site Analysis Program (SITES) was used to develop a model to analyze the integrity and stability of the auxiliary spillway for the ASH and IDF events. TR-60 requires that the stability of the auxiliary spillway (no loss of surface vegetation) be sufficient for the ASH and the integrity of the auxiliary spillway (no loss of reservoir storage) be sufficient for the FBH. No lab testing data was available to determine material properties of the soil in the auxiliary spillway. Golder, therefore, estimated the parameters using typical values from literature and experience. The results show a maximum exit velocity of approximately 14 ft/s and an integrity distance of approximately 440 feet during the ASH for existing conditions. The model predicts some erosion in the spillway but not a complete failure during the ASH event. The maximum exit velocity during the FBH event is approximately 25 ft/s. The model predicts that the auxiliary spillway will fail during the FBH event under existing conditions. 2.6 Natural Resources Survey Environmental investigations were conducted within the anticipated construction footprint to determine the presence of wildlife and wetlands vegetation that could be impacted during construction of any modifications that are warranted (ERO 2015). The footprints were developed based on an estimated impact area required for construction. 2.6.1 Wildlife Following a review of existing data sources, ERO Resources (ERO) conducted a field review of the FP-B1 study area on September 17, 2015 (ERO 2015). Observations of wildlife were recorded and habitat suitability for state sensitive species, federal Threatened and Endangered species, migratory birds, and raptors was evaluated during the site visit. ERO provided a draft wildlife memorandum summarizing wildlife resources potentially occurring in or affected by activities in the FP-B1 study area. Following is a summary of the findings of the site review and ERO’s recommendations for ensuring compliance with the requirements of The National Environmental Policy Act (NEPA), the Endangered Species Act, and other applicable regulations and NRCS policies.

Northern Pocket Gopher. The study area includes potential habitat for the northern pocket gopher; however, no eskers or other evidence of their presence were found during field survey. Therefore, it is unlikely that the northern pocket gopher occurs in this study area.

Swift Fox. The study area is at the extreme eastern edge of swift fox overall range (CPW 2014). Habitat in the study area is suboptimal due to the lack of native-shortgrass prairie typically preferred by swift fox and proximity to

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residences and other human disturbance. No swift foxes or their sign were observed in the study area, and it is unlikely that swift fox occur in the study area.

Federal Threatened, Endangered, or Candidate Animal Species. There is no likelihood for the proposed project activities to affect any federal threatened, endangered, or candidate animal species because of the lack of potentially suitable habitat in the study area.

Raptors and Other Migratory Birds. The FP-B1 study area provides breeding habitat for numerous ground- nesting bird species. At least one potential migratory bird nest was observed in the FP-B1 study area. Additionally, the grassland communities within the study area provide breeding habitat for ground nesting bird species such as the western meadowlark and vesper sparrow. No raptor nests were observed within ½ mile of the FP-B1 study area; however, scattered cottonwoods in the study area and vicinity provided potential nesting trees.

Raptors in Colorado are protected under the Migratory Bird Treaty Act (MBTA). Colorado Parks and Wildlife (CPW) division has published recommended buffer zones for nesting and breeding raptors in the state, which generally range from ¼ to ½ mile from a nest site, depending on the species (CDOW 2008). The U.S. Fish and Wildlife Service (USFWS) typically considers that implementation of the CPW buffers and seasonal restrictions fulfill compliance requirements of the MBTA for raptors.

NRCS policy is to avoid potential impacts on migratory birds to the extent possible by minimizing ground disturbance in migratory bird nesting habitat during nesting season. The nesting season in Colorado is March 15 through July 15. To the extent possible, conducting habitat-disturbing activities (such as tree removal, grading, scraping, and grubbing) in the nonbreeding season would minimize disturbance (or take) of an active migratory bird nest, including nests of ground-nesting species.

If the unintentional take of migratory birds, either individually or cumulatively, would result in a measurable negative effect on a migratory bird population, NRCS policy is to develop additional principles, standards, and practices in coordination with the USFWS to further lessen the amount of unintentional take. If construction must occur during March 15 through July 15, coordination with the USFWS is recommended to determine if preconstruction surveys or other measures, such as mowing, vegetation removal, or grubbing prior to the nesting season, are appropriate.

If habitat-disturbing activities may occur during the raptor breeding season, a pre-construction raptor nest survey within ½ mile of the study area is suggested. The typical breeding seasons for raptors in Colorado ranges from mid-February through July. 2.6.2 Vegetation On September 17, 2015, ERO Resources conducted a site investigation to identify and map the habitats present, record noxious weeds, and investigate the sites for potential habitat for threatened and endangered plants. Wetlands were mapped based on the presence of hydrophytic vegetation, which is a conservative approach since both hydric soils and wetland hydrology were assumed to be present (ERO 2015).

The dominant vegetation community in the study area is disturbed grassland, with a small area within the western portion containing remnants of short- and mid-grass prairie species. Within the eastern portion of the study area and upstream of the dam, it is dominated by smooth brome, curly dock, and leafy spurge. Although curly dock has a wetland indicator status of facultative and may occur in wetlands, it was present with smooth brome and leafy spurge, which are upland species. No wetlands or evidence of channel bed or bank was observed in the study area during the field survey.

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Seven noxious weed species on the Colorado Noxious Weed Inventory Lists B and C were observed in the study area. The survey area consisted of mostly scattered individuals to small populations with a cumulative vegetation cover of approximately 10 percent. 2.7 Cultural Resources Survey ERO conducted a Class III pedestrian survey of the FP-B1 study area in early September 2015 (ERO 2017). The cultural resource survey resulted in the documentation of two cultural resources: one historical reservoir (5DA3412) and one prehistoric open lithic scatter (5DA3413), both of which are recommended not eligible for listing on the National Register of Historic Places (NRHP). 2.8 Air Quality/Noise The dam is located in the Denver-Metro/North Front Range Region, which includes Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson, Larimer, and Weld counties. The region complies with all National Ambient Air Quality Standards, except for ozone and is designated non-attainment for ozone (CDPHE 2015). The nearest monitoring stations are in Douglas. Because the dams are in a non-attainment area, any activity that emits more than one ton per year of a criteria pollutant is required to submit an Air Pollutant Emission Notice (APEN) and Application for Construction Permit to the Colorado Department of Public Health and Environment, Air Quality Control Division (AQCD). Expected emissions, and the need for a permit, will be determined during detailed project design.

There are no records of ambient noise level near the dams. Douglas County currently does not have any noise ordinances in effect. 2.9 Hazard Classification Assessment The hazard classification of the facility was recently upgraded from a low hazard structure to a high hazard structure by the Colorado Division of Water Resources, Dam Safety Branch. (Colorado DWR 2016). Golder performed an independent review of the hazard classification (Golder 2018b). The results of that evaluation indicated that the hazard class could be modified to significant hazard if additional flood proofing/buyouts of one (1) residential structure were considered. This was considered as an option in developing alternatives, which are discussed subsequently.

As indicated previously, Colorado regulations allow for a smaller Inflow Design Flood (IDF) for the structures if an Incremental Drainage Assessment (IDA) indicates that minimal additional damage would occur as the result of a dam failure. As such, an IDA was conducted using the hydraulic model (previously developed by others) to determine the impacts between a no dam scenario and a dam breach scenario for various ratios of the PMP.

The reservoir safely attenuates the 1-percent annual chance (100-year recurrence interval) event without overtopping the embankment or causing the auxiliary spillway to activate. The existing spillway can safely convey the 0.2-percent annual chance (500-year recurrence interval) event. The embankment would overtop for events with magnitudes greater than the approximately 45-percent PMP event, and the reservoir would likely fail due to overtopping and ultimate erosion of the dam crest. In addition, the existing vegetation lined spillway would likely fail during this event. 3.0 ALTERNATIVES ASSESSMENT The proposed improvements will be designed to meet current State of Colorado and Natural Resource Conservation Service (NRCS) Dam Safety Requirements. The current hazard classification for the dam by the

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State of Colorado Department of Water Resources, Dam Safety Branch and NRCS is High Hazard (State of Colorado 2007, NRCS 2005). However, a preliminary Hazard Classification Report and additional hydrologic evaluations completed by Golder Associates Inc. (Golder 2018b) indicates that the appropriate hazard classification for the structure could be “Significant” if structural flood proofing modifications were made to one (1) structure in the downstream inundation zone and easement acquisitions were obtained for the area between the existing Federal Emergency Management Agency (FEMA) regulatory floodplain zone and the predicted “sunny day” failure dam breach zone. As such, the Inflow Design Flood (IDF) for the Franktown-Parker FP-B1 watershed dam could be 45-percent of the Probable Maximum Precipitation (PMP) event according to current State of Colorado and NRCS Dam Safety Standards. However, if the flood proofing modifications and easement acquisitions were not made, the dam would maintain its “High” hazard classification and would require the improvements to be designed for the required controlling IDF (based on current State of Colorado and NRCS dam safety criteria).

While both the embankment and emergency spillway structures are in good condition, modifications are required to safely pass the IDF (for both a Significant and High hazard classification) without overtopping the embankment as the dam was originally designed for a much smaller magnitude event.

Below is a summary of the hydrology used for evaluating alternatives, the design criteria adopted by Golder, preliminary alternatives under consideration, estimated implementation costs, and preliminary recommendations of a Preferred Alternative to be evaluated in further detail as part of the Final Design for the Baldwin Gulch FP-B1 watershed dam. Golder has completed the preliminary engineering evaluations to support the work, which will be summarized in the Investigation and Analysis Report included with the Watershed Plan. Alternatives for both the Significant and High Hazard classification of the structure were evaluated. 3.1 Existing Conditions Based on previous evaluations, the existing dam and appurtenant facilities (principal spillway and auxiliary spillway) are in good condition (Wilson 2016a). The existing geotechnical stability of the embankment meets all current State of Colorado and NRCS dam safety requirements (Golder 2018a). Further, the existing principal spillway can convey the 1-percent annual chance (100-year recurrence interval) runoff event (original design criteria) and has adequate freeboard for the Auxiliary Spillway Hydrograph (ASH) and Freeboard Hydrograph (FBH). However, the existing vegetated spillway includes berms and is in a “perched” condition which is not desirable and would suffer some erosional instability during the FBH.

The dam provides flood protection within downstream areas of Baldwin Gulch that has been developed in recent years and includes several road crossings which include:  Centennial Drive  Pine Drive  Village Creek Parkway  Lincoln Avenue  Parker Road  Twenty Mile Road

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All the existing roadway crossings, except for Centennial Drive, are adequate to convey the attenuated 100-year peak discharge from the reservoir. However, previous dam breach evaluations (Muller 2014) have indicated that if the dam were to fail, significant damages and overtopping of existing roadways would occur. Additional dam breach evaluations conducted by Golder (Golder 2018b) which included unsteady state hydraulic routing indicated that minor overtopping of Pine Drive, Village Creek Parkway and Parker Road would occur during a dam failure of FP-B1.

Photo D-2: FP-B1 Embankment and Spillway 3.2 Design Hydrology (Inflow Design Flood Analysis) The existing conditions hydrology was previously evaluated as part of the investigations and analysis of the existing structure using current State of Colorado Dam Safety Criteria (Wilson 2016b). For purposes of evaluating the alternatives, the hydrology estimates were refined to include both Colorado and NRCS criteria for both High Hazard and Significant Hazard classifications of the dam.

The current State of Colorado and NRCS design criteria for design storm depth is summarized in Table D-3 below:

Table D-3: Design Precipitation Depth Criteria Hazard Class Colorado NRCS

Significant 0.45PMP P100+0.40(PMP-P100)

High 0.90PMP Full PMP

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3.2.1 State of Colorado Methodology Using current State of Colorado Dam Safety criteria, the PMP storm depths were developed using HMR-55A methodology (State of Colorado 2007, USDC 1988). The 100 and 500-year, 24-hour recurrence interval precipitations depths were estimated from NOAA Atlas 14 (USDC 2013). A summary of the precipitation depths used in the hydrology analysis based on State of Colorado standards can be found in D-4 below.

Table D-4: Precipitation Depth Summary using State of Colorado Criteria Precipitation Depth (inches)

Significant High Hazard Hazard Criteria (90% PMP) (45% PMP)

General Storm PMP (24-hour Duration) 30.35 15.18

Local Storm PMP (6-hour Duration) 13.61 6.80

100-year Event (24-hour Duration) 4.71

500-year Event (24-hour Duration) 6.13

No reductions to the precipitation values were applied since the watershed is less than 10 square miles in aerial extent, and the site is below 6,000 feet in elevation. The local storm precipitation distribution was developed based on methods detailed in HMR-55A (USDC 1988). The general storm precipitation distribution was based on methods detailed in Bureau of Reclamation Flood Hydrology Manual (USBR 1989). The 100 and 500-year, 24- hour recurrence interval events were distributed using the SCS Type II distribution.

Runoff losses were determined by utilizing the Green and Ampt Loss method. The parameters were input into an HEC-HMS model to estimate the peak design discharges for the high and significant hazard dam safety classifications (USACE 2017). 3.2.2 NRCS Methodology The NRCS criteria for evaluating the safety of existing dams is documented in TR-60 (USDA 2005). A summary of the precipitation depths used in the hydrology analysis based on these standards can be found in Table D-5 below.

Table D-5: Precipitation Depth Summary Using NRCS Criteria Precipitation Depth (inches)

Significant High Hazard Hazard Criteria (FBH = 100% PMP) (FBH)

PMP (24-hour Duration) 33.73 16.32

100-year Event (24-hour Duration) 4.71

500-year Event (24-hour Duration) 6.13

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No reductions to the precipitation values were applied since the watershed is less than 10 square miles in aerial extent and the site is below 6,000 feet in elevation. The PMP events (FBH) storms were distributed using the dimensionless design storm distribution presented in Figure 2-4 in TR-60 while the 100 and 500-year, 24-hour recurrence interval events were distributed using the SCS Type II distribution.

Runoff losses were calculated using NRCS methods described in TR-60. The watershed consists of primarily undeveloped land with pinyon-juniper and oak-aspen cover. Soils within the watershed are generally clayey to sandy loams. Based on this land use cover and soil type, an estimated composite CN of 57 was calculated. This was adjusted to account for an Antecedent Runoff Condition (ARC) of III to account for saturated conditions within the watershed resulting in an effective CN of 75 (Table 10-1, NEH-4). The composite curve number calculation can be seen in Table D-6 below.

The parameters were input into the HEC-HMS model to estimate the peak design discharges for the high and significant hazard dam safety classifications.

Table D-6: Composite Curve Number (CN) Estimate Cover Type Vegetated1 Land Cover Rural1 Land Cover

Percent of Total Watershed 87% 13%

Oak-Aspen (Fair Condition) CN 48 (estimated 25% of vegetated area) -

Pinyon-Juniper (Fair Condition) CN 58 (estimated 75% of vegetated area) -

Developed (1/2 acre lots) CN - 70

Estimated Composite CN 57

For ARC III2 75 Notes: 1) Wilson 2016. 2) Table 10-1, NEH-4 (USDA 1972).

3.2.3 Auxiliary Spillway Hydrograph Analysis NRCS also required that the Auxiliary Spillway Hydrograph (ASH) also be estimated. The ASH is used to verify auxiliary spillway stability. For the ASH analysis, TR-60 specifies that the rainfall depth should be calculated for high hazard dams by the following equation (USDA 2005):

= + 0.26( )

𝑃𝑃Where𝐴𝐴𝐴𝐴𝐴𝐴 :𝑃𝑃 100 = Precipitation𝑃𝑃𝑃𝑃𝑃𝑃 − 𝑃𝑃100 Depth for ASH Analysis (in) = Precipitation Depth for 100-yr Event (in) 𝑃𝑃𝐴𝐴𝐴𝐴𝐴𝐴 = PMP Partial Duration Depth (in) 𝑃𝑃100

For calculation𝑃𝑃𝑃𝑃𝑃𝑃 of the ASH precipitation depth, the 24-hour duration was used to select the values of P100 and PMP. From Table D-6 above, the 24-hour duration PMP depth is 33.73 inches and the 100-year recurrence interval, 24-hour duration storm depth is 4.71 inches. Using the above equation, the auxiliary spillway precipitation depth (PASH) is 12.26 in. Because the watershed is less than 10 square miles, no aerial reduction factor has been applied.

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The depth of PASH was distributed as shown in Figure 2-4 in TR-60 which shows a dimensionless storm distribution for use in the auxiliary spillway hydrograph analysis. 3.2.4 Design Hydrology Summary Table D-7 provides a summary of the hydrologic evaluations undertaken.

Table D-7: Inflow Design Flood Analysis Summary Peak Depth Inflow Storm Event (in) (cfs) Standard

High Hazard

FBH1 – 100% PMP 33.73 8061 NRCS

90% Local Storm2 – EM111.2.1411 13.61 13561 Colorado DWR

90% Local Storm2 – HMR-5 13.61 13095 Colorado DWR

90% Local Storm2 – USBR 13.61 14226 Colorado DWR

90% General Storm3 – USBR 30.35 16771 Colorado DWR

ASH 12.26 2525 NRCS

Significant Hazard

FBH1 16.32 3592 NRCS

45% Local Storm1 – EM111.2.1411 6.80 6186 Colorado DWR

45% Local Storm1 – HMR-5 6.80 5917 Colorado DWR

45% Local Storm1 – USBR 6.80 6460 Colorado DWR

45% General Storm2 – USBR 15.18 7830 Colorado DWR

ASH1 8.19 1477 NRCS

100-year/24-hour4 4.71 1730 Colorado DWR & NRCS

500-year/24-hour4 6.12 2574 Colorado DWR & NRCS Notes: 1) Table 2-5 in TR-60. Distributed using dimensionless design storm distribution in Figure 2-4. (NRCS 2005). 2) Local storm distributions were developed based on methods detailed in Section 12 of Hydrometeorological Report No. 55A (HMR-55A) (USDC 1988). 3) General storm distribution based on methods detailed in Section 3.4 of the Bureau of Reclamation, Flood Hydrology Manual (USBR 1989). 4) SCS Type 2 Distribution.

September 4, 2019 1911774-2000-3-R-3 Appendix D

3.3 Design Criteria Design criteria that will be used to evaluate and compare alternatives are based on current NRCS and State of Colorado Division of Water Resources requirements. Table D-8 summarizes the design criteria that will be used to evaluate and compare the alternatives.

Table D-8: Watershed Dam FP-B1 Design Criteria for Significant & High Hazard Alternatives Criteria Value Source

Embankment

Min. Design Crest Elevation (feet) 5,963.6 As-built survey

Min. Design Crest Width (feet) 13 Colorado DWR regulations

Max. Side Slope 2½H:1V Stability analysis

Max. RCC Overtopping Velocity (fps) 30 USBR guidelines

Max. ACB Overtopping Velocity (fps) 30 Manufacturer’s recommendation

Max. Reinforced Vegetation Overtopping Velocity (fps) 30 Manufacturer’s recommendation

Static Embankment Stability Factor of Safety 1.5 Colorado DWR/NRCS regulations

Rapid Drawdown Factor of Safety 1.2 Colorado DWR/NRCS regulations

Pseudo-static Embankment Stability Factor of Safety 1.0 Colorado DWR/NRCS regulations

Spillway Capacity

Min. Design Crest Elevation (feet) (100-year WSEL) 5,958.7 Golder hydrologic analysis Notes: 1) Golder Hydrologic Analysis (Golder 2018b) 2) Colorado DWR Regulations (State of CO 2006) 3) TR-60 – NRCS Regulations (NRCS 2005) 4) All elevations are NAVD88. 3.4 Preliminary Alternatives The proposed improvements will be designed to meet current State of Colorado and NRCS dam safety requirements and will likely require modifications to the dam and/or spillway structures. Preliminary alternatives that have been identified for further evaluation include the following: Future without Project/No Action Alternative The No Action Alternative is a required alternative (NWPH 2014, Sec 601.10b). For dams that pose a potential safety hazard from failure, the future-without-project (FWOP) plan or no-action alternative is based on the course of action that the sponsors are most likely to take in the event that no federally financed rehabilitation work was to be undertaken. This includes a deliberate breach. A deliberate breach would be likely to reduce safety risks as compared to a sudden, catastrophic dam failure. This alternative is not considered to be viable as the dam would not meet the Purpose and Need; downgradient residences and flood conveyance structures would no longer have adequate flood protection. However, NRCS requires that this alternative be used as a baseline to compare the action alternatives listed below.

September 4, 2019 1911774-2000-3-R-3 Appendix D

Decommissioning Decommissioning would involve reducing the embankment height and storage volume to a level where the dams are not considered to be jurisdictional structures (less than 10 feet high and 100 acre-feet of storage volume) by either State of Colorado or NRCS standards. Decommissioning would greatly reduce the flood attenuation benefit of the facilities and result in higher peak discharges. Flooding downstream during lower magnitude storm events would likely increase. The decommissioning alternative differs from the FWOP in that it would use federal funds and, thus, be required to meet NRCS standards. As such, conveyance improvements would be required at several downstream road crossings to maintain the flood control benefit associated with the dam. Modifications to the Existing Spillway Modifications to the existing spillway could be implemented to increase the conveyance capacity and reduce the potential for overtopping of the embankment. These alternatives include:  Installation of hydraulically efficient crest structures (ogee, labyrinth)  Crest lowering and installation of fuseplugs/fusegates  Widening/lowering of the existing spillway Based on previous discussions with the NRCS, fuseplugs are not approved under a Categorical Exclusion (CE) and would require a variance. As such, this alternative was determined to be not feasible and was not evaluated further. Increased Freeboard (Embankment Crest Raise) The embankment could be raised to increase spillway conveyance discharges and minimize the potential for overtopping. The embankment would be raised using either downstream, centerline, or upstream construction methods. However, residential structures located upstream have base elevations similar to the maximum pool crest elevation. As such, this alternative was determined to be not feasible and was not evaluated further. Overtopping Protection Overtopping protection of the embankment (or a section of the embankment) could be implemented to protect the embankment from erosion and potential failure. Overtopping protection alternatives include:  Roller-compacted concrete (RCC)  Articulated concrete blocks (ACB)  Geosynthetics or other turf reinforcement mats (TRM) To improve aesthetics of the proposed modifications, the overtopping protection could be covered with topsoil and a native seed mix applied to provide for a more natural landscape. Temporary irrigation and erosion control measures would be required to ensure that adequate vegetation is established. In addition, if the improvements were activated during a flooding event, replacement of the topsoil and vegetation would be required.

Based on previous discussions with the NRCS, articulated concrete blocks (ACB) and turf reinforcement mats (TRM) are not acceptable methods for overtopping protection and, as such, were determined to be not feasible.

September 4, 2019 1911774-2000-3-R-3 Appendix D

Roller Compacted Concrete (RCC) Auxiliary Spillway A roller compacted concrete (RCC) spillway could be constructed within the dam embankment to serve as the primary auxiliary spillway for the facility The existing earthen auxiliary spillway would be abandoned. The proposed auxiliary spillway would be constructed in an excavated section of the main embankment. It would include reinforced concrete cutoff and training walls as well as roller compacted concrete (RCC) on the face of the dam to minimize erosion potential on the embankment.

To improve aesthetics of the proposed modifications, the overtopping protection could be covered with topsoil and a native seed mix applied to provide for a more natural landscape. Temporary irrigation and erosion control measures would be required to ensure that adequate vegetation is established. In addition, if the improvements were activated during a flooding event, replacement of the topsoil and vegetation would be required. Downstream Flood Proofing and RCC Auxiliary Spillway The Hazard Classification Report and hydrologic evaluations completed by Golder indicate that the appropriate hazard classification may be lowered to “Significant” from “High” if flood proofing measures of one (1) structure downstream were implemented. As such, a proposed roller compacted concrete (RCC) spillway could be constructed within the dam embankment in conjunction with flood proofing of the hazards immediately downstream of the dam. Flood proofing downstream hazards would allow the classification to be reduced to “Significant” as the hazards would ultimately be inconsequential. Like the previous RCC spillway alternative, this proposed spillway will serve as the primary auxiliary spillway for the embankment structure. The proposed spillway would be constructed in an excavated section of the main embankment. It would include reinforced concrete cutoff and training walls as well as roller compacted concrete (RCC) on the face of the dam to minimize erosion potential on the embankment. Easements would also be required to limit development that could occur in the zone between the estimated 100-year floodplain extents and the estimated dam breach extents. Principal Spillway Replacement and RCC Auxiliary Spillway Improvements to the principal spillway would include a larger cast-in-place concrete riser structure and pre-cast concrete box culvert outlet to allow for higher discharge rates for larger storms while maintaining existing conditions for smaller storm events. The proposed improvements would be constructed in conjunction with an RCC auxiliary spillway that would replace the existing auxiliary spillway. It would include reinforced concrete cutoff and training walls as well as roller compacted concrete (RCC) on the face of the dam to minimize erosion potential on the embankment.

These alternatives are discussed in more detail in the sections below. 3.4.1 Alternative 1 – No Action/Future without Project Under this alternative, no modifications to the spillway would be made. The existing high hazard classification would remain in-place and, as such, the structure would not meet the required NRCS and State of Colorado Dam Safety requirements for the spillway. A likely outcome would be that the State of Colorado Dam Safety Division would require that the dam be deliberately breached by the Project Sponsor using non-Federal funds. A section of the dam would be breached to a minimum height of 6 feet above the existing Baldwin Gulch channel and the primary spillway converted to a water quality structure. The width of the breach would be approximately 200 feet.

Figure D-1 provides a plan view and sections of the proposed conceptual breach configuration of this alternative.

September 4, 2019 1911774-2000-3-R-3 Appendix D

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Minimizes construction costs  Reduces flood control benefits in downstream areas  Changes use of structure  Minimizes water quality and sediment deposition benefits

3.4.2 Alternative 2 – Decommissioning Under this alternative, the embankment would be breached and armored to protect from erosion. This would likely be the minimum action required to meet Colorado Dam Safety Criteria without any modifications to increase spillway capacity. Since the dam would be breached, minimal flood attenuation would occur, greatly reducing the flood control benefit of the dam. The breach was sized based on flood routing calculations to pass the appropriate IDF for the structure assuming a maximum 9-foot flow depth (assuming 1 foot of freeboard). The remainder of the embankment would remain in its existing condition. The breach would be trapezoidal in shape (with a 3H:1V side slope) and armored. However, erosion of the channel through the breach during larger flood events would be likely. The calculated breach width to meet the above criteria is 200 feet. The maximum velocity during the IDF through the breach is estimated to be approximately 12 fps. This alternative differs from the Future without Project alternative in that Federal funds would be used and, as such, protection of downstream properties and infrastructure would be required (including improvements to downstream roadway conveyances to prevent overtopping).

Figure D-2 provides a plan view and sections of the proposed conceptual breach configuration of this alternative. A meandering low-flow channel could also be re-established through the breach, and the floodplain bench could be vegetated with riparian vegetation. The side slopes would be armored with riprap to minimize the potential for lateral erosion.

Photo D-3: Decommissioning Alternative

September 4, 2019 1911774-2000-3-R-3 Appendix D

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Minimizes construction costs  Reduces flood control benefits in downstream  Re-establishes natural channel system areas  Changes beneficial use of existing structure  Minimizes water quality and sediment deposition benefits

3.4.3 Alternative 3 – Existing Auxiliary Spillway Widening This alternative consists of widening the crest of the spillway by construction of a 210-foot-wide reinforced concrete side channel spillway structure in addition to widening and lowering the downstream spillway channel to reduce velocities and remove the perched spillway condition. The side channel spillway would be constructed in conjunction to downstream flood proofing measures and would be capable of passing the discharge from the 45% General Storm PMP event. Downstream flood proofing measures would lower the dam hazard classification from “High” to “Significant.” The downstream spillway channel would be widened to 150 feet which would convey the required IDF without susceptibility to erosion and overtopping of the dam. Total flow through the spillway is estimated to be approximately 7,200 cubic feet per second (cfs). The construction of this alternative would require easements of induced flooding areas and land within the 1% flood to prevent future construction of home and commercial structures. As a large portion of this land has been recently platted for single-family residential structures, these easements could be relatively costly. Figure D-3 provides a plan view and cross section of the proposed conceptual design of this alternative.

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Prevents the potential of an overtopping failure  Relatively high construction costs during the IDF for a high hazard rating; Meets  Requires reinforcement of vegetated spillway regulatory requirements section  Maintains flood control benefit of structure  Requires obtaining easements for downstream  Maintains existing spillway function land between the existing 100-year regulatory floodplain and the estimated dam breach zone to prevent future development that could raise the hazard classification

3.4.4 Alternative 4 – Overtopping Protection For this alternative, the embankment would be protected from overtopping flows during the IDF using either Roller Compacted Concrete (RCC), Turf Reinforcement Mats (TRM), or Geosynthetics or Articulated Concrete Blocks (ACB). The maximum overtopping flow for Watershed Dams FP-B1 is approximately 2 feet across the entire embankment crest, and the associated anticipated velocities on the face of the dam would be acceptable for the use of these materials. Excavation of the crest and downstream face would be required to maintain the existing geometry of the slope after installation of the overtopping protection. Topsoil and vegetation could be used to cover the erosion resistant overtopping protection to maintain the aesthetics of the embankments. A 30-foot wide RCC or ACB apron and end sill wall are also required at the toe of the dam to minimize the potential for scour.

September 4, 2019 1911774-2000-3-R-3 Appendix D

The principal spillway would be replaced to meet NRCS design standards for a dam with a high hazard classification. The new principal spillway would consist of a drop inlet with a two-way, reinforced concrete, covered riser (4 feet wide by 8 feet long by 15.0 feet high) and a 30-inch diameter, steel pipe encased in reinforced concrete outlet conduit. The outlet conduit pipe would include a 20-inch orifice plate to ensure the same discharge during the 100-year recurrence interval event.

Figure D-4 provides a plan view and cross section of the proposed conceptual design of this alternative.

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Prevents the potential of an overtopping failure  Relatively high construction costs during the IDF; Meets regulatory requirements  Larger construction footprint  Maintains flood control benefit of structure  Maintenance of existing vegetated spillway  Maintains existing spillway function  Aesthetics if not covered with topsoil and re- vegetated which requires maintenance

3.4.5 Alternative 5 – Roller Compacted Concrete (RCC) Auxiliary Spillway This alternative consists of constructing a roller compacted concrete (RCC) spillway section and abandoning the existing earthen auxiliary spillway. The proposed auxiliary spillway would be constructed in an excavated section of the main embankment. It would include reinforced concrete cutoff and training walls as well as RCC on the face of the dam to minimize erosion potential on the embankment. The proposed RCC spillway would be approximately 470 feet wide with a crest elevation of approximately 5,958.8 feet and would be capable of conveying the runoff from the high hazard classification IDF event without overtopping the dam, meeting both the State of Colorado and NRCS dam safety requirements for a High Hazard structure.

NRCS and Colorado Dam Safety rules require that the Douglas County protect property and homes in the flood pool surcharge area (upgradient of the dam) from inundation by obtaining easements or protecting dwellings by floodproofing. The inundation footprint incudes several discontinuous areas (total about 2.5 acres) that are outside the current easement controlled by Douglas County. In addition, there are two home that would be partially inundated by the IDF flood pool. The areas are shown on Figure C-6 in Appendix C. A berm would be constructed within the county easement boundary to protect property and structures from inundation during the IDF.

Figure D-5 provides a plan view and profile of the proposed spillway.

Advantages and disadvantages of this alternative are summarized in the table below:

September 4, 2019 1911774-2000-3-R-3 Appendix D

Advantages Disadvantages  Prevents the potential of an overtopping failure  Moderate high construction costs during the IDF; Meets NRCS and State of  Requires maintenance of the RCC overtopping Colorado regulatory requirements section  Maintains flood control benefit of structure  Aesthetics if not covered with topsoil and re-  Maintains existing spillway function vegetated which requires maintenance

Photo D-4: Typical RCC Embankment Spillway

3.4.6 Alternative 6 – Hazard Reclassification through RCC Auxiliary Spillway Construction and Downstream Flood Proofing Like the previous alternative, this alternative consists of excavating the embankment and constructing a roller compacted concrete (RCC) spillway section. However, this spillway would be constructed in conjunction with flood proofing measures and easement acquisitions downstream to minimize potential hazards downstream, allowing for a “Significant” hazard classification of the structure to be obtained. The existing auxiliary spillway on the right abutment would be maintained and a new RCC auxiliary spillway section would be added on the face of the embankment. The proposed RCC spillway would be approximately 135-feet-wide with a crest elevation of approximately 5,958.8 feet. The layout of the proposed improvements would be similar to that for the High Hazard spillway with the exception that the RCC spillway width would be smaller. The construction of this alternative would require easements of induced flooding areas and land within the 1-percent recurrence interval flood to prevent future construction of home and commercial structures.

This alternative also includes replacement of the existing principal spillway as in Alternative 5.

Figure D-6 provides a plan view and profile of the proposed modifications for this alternative.

September 4, 2019 1911774-2000-3-R-3 Appendix D

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Prevents the potential of an overtopping failure  Requires flood proofing one (1) residential during the IDF; Meets regulatory requirements structure  Maintains flood control benefit of structure  Requires obtaining easements for downstream  Maintains existing spillway function land between the existing 100-year regulatory floodplain and the estimated dam breach zone to prevent future development that could raise the hazard classification  Requires maintenance of the existing earthen spillway

3.4.7 Alternative 7 – Principal Spillway Replacement and RCC Auxiliary Spillway This alternative consists of excavating and removing the principal spillway and replacing it with a larger cast-in- place reinforced concrete inlet riser and box culvert outlet. This would allow for increased discharge rates through the principal spillway during the lower frequency of occurrence storm events. The proposed riser would be constructed in addition to a roller compacted concrete (RCC) spillway section. Hydrologic/hydraulic evaluations indicated that installing a riser structure capable of passing the entire IDF is not feasible due to the large size of the riser and outlet required. As such, an RCC spillway would also be required to convey the IDF and replace the existing auxiliary spillway on the right abutment. The existing auxiliary spillway profile would be decommissioned.

The proposed concrete riser structure would be approximately 5-feet by 15-feet with a 4ft x 6in low level orifice to control the discharges of smaller storms and provide for a water quality benefit. The outlet would be replaced with a 12 ft by 5 ft reinforced concrete box culvert (RCBC). To maintain flood control benefits during the 100-year and 500-year recurrence interval events, the RCC spillway would be approximately 420 feet wide with a crest elevation of approximately 5,958.8 feet for the full PMP event.

Figure D-7 provides a plan view and profile of the proposed modifications for this alternative.

Advantages and disadvantages of this alternative are summarized in the table below:

Advantages Disadvantages  Prevents the potential of an overtopping failure  Moderate construction costs during the IDF; Meets regulatory requirements  Aesthetics if not covered with topsoil and re-  Maintains flood control benefit of structure vegetated which requires maintenance  Maintains existing spillway function  Changes in 100-year and 500-year recurrence interval flood discharges requiring additional floodplain management

3.5 Hydrologic & Hydraulic Evaluations of Alternatives To estimate the impacts of the proposed alternatives on the downstream floodplain, the existing conditions hydrologic model was modified to include the proposed alternatives. As previously stated, the dam is currently classified as a “High” Hazard facility. However, additional alternatives were evaluated assuming that a Significant Hazard classification could be maintained with downstream flood proofing measures and easement acquisitions. The following alternatives were evaluated using the hydrologic model developed for the base line evaluations:

September 4, 2019 1911774-2000-3-R-3 Appendix D

 Alternative 1 – FWOP  Alternative 2-Decommissioning  Alternative 3-Existing Auxiliary Spillway Widening (Significant Hazard)  Alternative 4-RCC Overtopping Protection  Alternative 5-RCC Auxiliary Spillway  Alternative 6-RCC Auxiliary Spillway (Significant Hazard)  Alternative 7-Principal Spillway Replacement and RCC Auxiliary Spillway Table D-9 on the following page provides a summary of the evaluations undertaken for the considered alternatives.

September 4, 2019 1911774-2000-3-R-3 Appendix D

Table D-9: Watershed Dam FP-B1 Design Criteria for Significant & High Hazard Alternatives Existing Conditions No Dam (Decommissioning) Widened Spillway (210 ft) RCC Spillway (470 ft) Flood Proofing w/RCC (135 ft) Outlet Spillway w/RCC (420 ft) Crest of Dam = 5963.6 ft Peak Elev. Discharge (cfs) Discharge (cfs) Elev. (feet) Discharge (cfs) Elev. (feet) Discharge (cfs) Elev. (feet) Discharge (cfs) Elev. (feet) Discharge (cfs) Elev. (feet) (feet) High Hazard - 90% PMP

Peak Qin 16771 5965.7 16771 N/A N/A N/A 16771 5963.6 N/A N/A 16771 5963.6

Peak Qout 16713 16771 N/A 16577 N/A 16605

Downstream Watershed - Peak Qout 11654 11654 N/A 11654 N/A 11654

@ Cherry Creek - Peak Qout 27605 27914 N/A 27270 N/A 27336 Significant Hazard - 45% PMP

Peak Qin 7830 5964.7 7830 N/A 7830 5963.6 N/A N/A 7830 5963.6 N/A N/A

Peak Qout 7708 7830 7281 N/A 7318 N/A

Downstream Watershed - Peak Qout 5511 5511 5511 N/A 5511 N/A

@ Cherry Creek - Peak Qout 12341 12944 11649 N/A 11677 N/A ASH - High Hazard Peak Qin 2525 5963.3 2525 N/A N/A N/A 2525 5960.2 N/A N/A 2525 5960.2 Peak Qout 2336 2525 N/A 2508 N/A 2510

Downstream Watershed - Peak Qout 1780 1780 N/A 1780 N/A 1780 @ Cherry Creek - Peak Qout 3856 4242 N/A 4180 N/A 4185 ASH - Significant Hazard Peak Qin 1477 5961.7 1477 N/A 1477 5960.3 N/A N/A 1477 5960.5 N/A N/A Peak Qout 1099 1477 1337 N/A 1328 N/A

Downstream Watershed - Peak Qout 1041 1041 1041 N/A 725 N/A @ Cherry Creek - Peak Qout 1775 2467 2156 N/A 1651 N/A 100-year

Peak Qin 1730 5958.7 1730 N/A 1730 5958.7 1730 5958.7 1730 5958.7 1730 5958.8

Peak Qout 40 1730 40 40 40 38

Downstream Watershed - Peak Qout 1291 1291 1291 1291 1291 1291

@ Cherry Creek - Peak Qout 1296 2662 1296 1296 1296 1296 500-year

Peak Qin 2574 5960.5 2574 N/A 2574 5959.7 2574 5959.4 2574 5959.9 2574 5959.3

Peak Qout 384 2574 674 849 627 978

Downstream Watershed - Peak Qout 1869 1869 1869 1869 1869 1869 @ Cherry Creek - Peak Qout 1884 4038 1888 1889 1887 1889

September 4, 2019 1911774-2000-3-R-3 Appendix D

A previous hydraulic model was developed as part of the hazard classification study for the dam (Golder 2018b). The peak flows from the hydrologic analysis were input into the hydraulic model for the alternatives being considered to determine the estimated downstream impacts associated with the alternatives. For the decommissioning alternative, peak discharges and flooding elevations during the 1-percent annual chance (100-year recurrence interval) event would increase and both Pine Drive and Parker Road would be overtopped. For the RCC spillway and modified existing spillway alternatives, peak discharges and water surface elevations during the 1-percent annual chance (100-year recurrence interval) event would remain essentially the same. For all alternatives evaluated, the existing Centennial Drive would be overtopped during the 1-percent annual chance (100-year recurrence interval) event and therefore, it is recommended that the crossing be modified to ensure access to upstream residents during flooding events is maintained. However, there is a secondary entrance into the developed area which may be adequate during emergency situations.

Figures D-8, D-9, and D-10 provide hydraulic profiles of Baldwin Gulch downstream of the dam for the various alternatives considered compared to existing conditions for the 100-year, 500-year and IDF events, respectively. It should be noted that the flows for the RCC overtopping protection should not deviate from existing conditions. As such, hydraulic profiles for RCC overtopping protections are not provided.

During the Inflow Design Flood (IDF) event (which was determined to be 90-percent of the Probable Maximum Precipitation (PMP) for a High Hazard facility using USBR rainfall/runoff methodology), all the downstream roadways would be inundated. 3.6 Comparative Estimated Implementation Costs Implementation costs for the alternatives presented above were estimated based on unit rates of similar projects in Metro Denver and preliminary unit rates from vendors. Table D-10 below provides a summary of the estimated implementation costs for the alternatives for Watershed Dams FP-B1. The costs were estimated for comparative purposes only and include 25-percent contingency. Attachment D1 provides a breakdown of the quantities and unit rates used to determine the implementation costs.

Table D-10: Estimated Implementation Costs Estimated Alternative Cost

Alternative 1-No Action/Future Without Project $27.2M

Alternative 2-Decommissioning $27.8M

Alternative 3-Existing Auxiliary Spillway Widening (Significant Hazard Classification) $25.7M

Alternative 4-RCC Overtopping Protection $7.0M

Alternative 5-RCC Auxiliary Spillway (High Hazard Classification) $3.0M

Alternative 6-RCC Auxiliary Spillway (Significant Hazard Classification) $24.6M

Alternative 7-Principal Spillway Replacement and RCC Auxiliary Spillway $3.2M

The decommissioning alternative includes provisions for conveyance upgrades that would be required at Pine Drive, Lincoln Avenue and Parker Road with the dam removed. In addition, the significant hazard alternatives include estimated costs for easement acquisitions in the area between the 1-percent annual chance (100-year

September 4, 2019 1911774-2000-3-R-3 Appendix D

recurrence interval) regulatory floodplain and the estimated dam breach zone to limit development within this area that could impact the future hazard classification of the facility. Estimates from the Douglas County real estate office indicates that these property values could be on the order of $23 million. Figure D-11 provides an overview of the estimated dam breach zone compared to the FEMA regulatory floodplain extents. 4.0 ECONOMIC EVALUATIONS Economic evaluations were undertaken to determine the estimated benefits of rehabilitating the Franktown-Parker FP-B1 (Baldwin Gulch) Watershed Dam (NID ID: CO056129). If the dam is not modified to meet current State and Federal dam safety requirements, it is likely that the State of Colorado Dam Safety Division would require that the dam be deliberately breached by the Project Sponsor using non-Federal funds. A section of the dam would be breached to a minimum height of 6 feet above the existing Baldwin Gulch channel and the primary spillway converted to a water quality structure. The benefit associated with implementing dam safety improvements to the dam is the reduction in damages associated with keeping the dam in service.

It should be noted that land has recently been platted by Douglas County for high-end single-family residence construction in the estimated dam breach zone and, as such, future benefits associated with maintaining the dam would likely be greater. 4.1 Hydrology and Flooding Extents The original structure was designed to store the 1-percent annual chance (100-year recurrence interval) flooding event without overtopping of the auxiliary/emergency spillway. The majority of benefits are associated with flood attenuation within the reservoir for events up to the 0.2-percent annual chance (500-year recurrence interval) event. Previous hydrologic evaluations related to extreme storm events (floods with magnitudes greater than the 50-percent Probable Maximum Precipitation (PMP)) conducted as part of the hazard classification and alternatives investigations indicate that the realized benefits for these extreme floods are not as great as the benefits for the more frequent flooding events.

The existing hydrologic model developed for the facility was revised to incorporate these frequency storms and the results of the model are consistent with values reported in the Flood Insurance Study (FIS) for Douglas County, Colorado (FEMA 2016) and the original design for the structure. The 2-year recurrence interval maximum water surface elevation within the reservoir is near the principal spillway crest and the 100-year maximum water surface elevation is estimated to be just below the auxiliary/emergency spillway crest of the structure. The structure can safely pass the runoff from the 0.2-percent annual chance (500-year recurrence interval) event with residual freeboard through the auxiliary spillway. 4.1.1 Estimation of Flooding Extents, Depths, and Velocities The peak discharges for the 1-percent annual chance (100-year recurrence interval) event for the with dam and without dam scenarios were input into a hydraulic model developed by Golder to determine floodplain extents, velocities and flooding depths downstream of the dam. In general, the attenuated flows with the dam in place for the 100-year and 500-year recurrence interval events are confined to the main portion of the Baldwin Gulch channel with minimal spreading on to the floodplain. With the dam removed, the floodplain extents, depths, and velocities increased significantly, and several roadways (including Parker Road and Pine Drive) would be overtopped. Figure D-12 shows the approximate 100-year recurrence interval flooding extents with and without the dam in place. Figures D-13 and D-14 show the approximate 100-year and 500-year recurrence interval flood

September 4, 2019 1911774-2000-3-R-3 Appendix D

profiles, respectively with and without the dam in place. Figure D-15 shows the approximate 500-year recurrence interval flood extents with the existing dam and the proposed rehabilitation alternative. 4.2 Damage Estimates Damage estimates for the with and without dams were determined based on estimating structural and land values located within the inundated area and estimating damages based on approximate depth and velocities and Federal Insurance Administration (FIA) US Army Corps of Engineers (USACE) depth damage curves (FIA 1999 and USACE 1992). Costs for disruption of traffic and environmental damages were also estimated. Present worth and average annual damages were estimated by annualizing the estimated damages for the various frequency events. A summary of the damage estimates is provided in Attachment D2. 4.2.1 Value Determinations Values of land and structures within the floodplain extents for the “with” and “without” dam scenarios were based on Douglas County Tax Assessor’s Geographical Information (GIS) database. The floodplain extents were used to develop a tabulation of impacted parcels, structure and land values, structure type, land type and land area. The values estimated in the database were tabulated and organized into land and structure type. Table 1 provides a summary of the GIS database values and Table 2 provides a summary of the data by land and structure type. The following structures were determined for use in determining damage estimates:  Single-level Residential Structure ...... SL  Single-level Residential Structure with Basement ...... SLB  Two-story Residential Structure ...... TS  Two-story Residential Structure with Basement ...... TSB  Commercial Structure ...... OS  Mobile Home ...... MH These structure classifications are consistent with Federal Insurance Administration (FIA) categories.

Table 3 lists the total value of the land, structure, and contents for the various structure types for the parcels located within the 100-year floodplain extents with and without the dams in place. Contents are estimated at 30% of structure value. 4.2.2 Estimation of Damages Damage estimates for the with and without dams were determined based on the estimated structural, land and contents values located within the inundated area, and damages were estimated based on approximate depth and velocities and Federal Insurance Administration (FIA) and US Army Corps of Engineer’s depth damage curves for the various structure types. In general, the depths increased by 1.0 to 3.0 foot for the “with” and “without” dam scenarios and velocities increased by 0.5 to 3 feet per second (fps) during the 100-year and 500- year recurrence interval events. Average depths are between 0.5 and 1.5 feet across the floodplain extents for the no dam scenario.

For purposes of estimating damages, the average depth-damage relationship from FIA and USACE depth- damage curves was assumed to be between 1 to 2 feet within the floodplain inundation extents for the various structure types that would be potentially impacted.

September 4, 2019 1911774-2000-3-R-3 Appendix D

The percent damages for the other frequency events were estimated based on the approximate difference in peak flow rate for the various frequency events compared to the 100-year recurrence interval event. The existing Baldwin Gulch channel and roadway crossings can convey the 500-year recurrence interval event (with the dam in place). The following damage reductions were assumed for the various frequency events incorporated in the analysis:  500-year ...... 116%  100-year ...... 100%  50-year ...... 43%  10-year ...... 4%  5-year...... 0%  2-year...... 0% Other estimated costs associated with flooding include emergency services costs, clean-up and maintenance costs, agricultural losses, water quality/environmental damages, disruption to traffic and roadway damages and damage to infrastructure (water, sewer, power, and telecommunications). These costs were based on assumed relationships as provided below:  Emergency Services Costs 8% of structural and contents damages  Clean-up/maintenance Costs 5% of structural and contents damages  Environmental Damages $1,500 per acre within riparian areas impacted  Roadway Damages $50,000 per crossing impacted  Infrastructure Damages $25,000 per utility impacted  Traffic Disruption Costs Based on information from Douglas County Engineering traffic study (42,300 total traffic hours @ $14.80/hour)

Parker Road, Pine Drive, and Centennial Drive would overtop during the 100-year frequency event without the dam in place and, as such, traffic disruption costs and potential damages would likely occur. Parker Road is a major arterial road with an estimated average daily traffic (ADT) count of 48,000 vehicles/day. In addition, Lincoln Avenue is classified as a major road with an estimated average daily traffic of 13,000 vehicles/day. ADT for Village Creek Parkway was estimated at approximately 2,500 vehicles/day. Traffic disruption costs were based on an assumed 1-week closure time for repairs and a traffic study conducted by Douglas County (Douglas County Engineering, 2018). Based on the hydraulic evaluations undertaken, it was assumed that no damage to roadways or infrastructure would occur for events with magnitudes less than the 10-year recurrence interval event.

Additional costs were also added for alternatives that involve decommissioning or removal of the dam to account for additional floodplain management associated with changes to the 100-year recurrence interval floodplain downstream of the dam.

The Population at Risk (PAR) during a potential dam breach was also estimated utilizing spreadsheets developed by the NRCS. The PAR is estimated to be 13 (see Attachment D3).

September 4, 2019 1911774-2000-3-R-3 Appendix D

4.3 Benefit-Cost Evaluations Based on economic evaluations that were undertaken, the estimated average annual benefits are approximately $51,630 with a present worth of approximately $1.7 million (assuming a 100-year project life and a 2.875% discount rate). The benefit-cost ratio of the various alternatives was based on the estimated benefits (reduction in damages) of bringing the dam into compliance with current dam safety requirements divided by the cost of the alternative. For the No Action and Decommissioning alternatives, additional costs for roadway conveyance improvements were included in the costs of implementation. Estimated operational and maintenance costs over the 100-year project life were included in the cost estimates. The RCC auxiliary spillway (High Hazard Classification) (Alternative 5) alternative had a benefit cost ratio of approximately 0.6 and highest overall benefit- cost ratio of the alternatives considered.

Table D-11 includes an alternative evaluation matrix that compares other criteria such as implementation costs, feasibility of implementation, public safety, construction risk, feasibility of funding and operation and maintenance used in evaluating the alternatives as well as a comparison of the benefits and costs of the alternatives. The following factors and weighting criteria were developed for each of the alternatives:  Implementation Costs ...... 15%  Feasibility of Implementation ...... 20%  Public Safety ...... 25%  Construction Risk ...... 20%  Feasibility of Funding ...... 10%  Operation and Maintenance ...... 10% Based on the results of the evaluation matrix, the RCC auxiliary spillway (High Hazard) alternative had the highest overall rankings using these other criteria. 5.0 SUMMARY AND RECOMMENDATIONS The most cost-effective alternative is to construct a new 470-foot-wide RCC auxiliary spillway within the embankment to accommodate the IDF for a High Hazard dam classification and replacement of the existing principal spillway to meet NRCS requirements for a high hazard facility. This is more cost effective then the Significant Hazard alternatives as land within the potential dam breach zone has recently been platted by Douglas County for single family residence construction and, as such, the Significant Hazard alternatives would require the purchase of high value property which would make the alternatives cost prohibitive.

This alternative has an estimated benefit-cost ratio of approximately 0.6.

Decommissioning of the dam would change the beneficial use of the structure and increase flood hazards downstream during more frequent runoff events (100- to 500-year recurrence interval events). These increases in discharges would cause Pine Drive, Lincoln Avenue and Parker Road to become overtopped during the 100-year recurrence interval event and, as such, additional road crossing improvements would be required which would add to the overall project costs.

September 4, 2019 1911774-2000-3-R-3 Appendix D

6.0 REFERENCES Carter Burgess. 2003. Phase 2 Baldwin Gulch Floodplain Modifications As-Constructed Drawings. July.

Colorado Division of Wildlife (CDOW). 2008. Recommended Buffer Zones and Seasonal Restrictions for 42 Colorado Raptors. Available at: https://cpw.state.co.us/Documents/WildlifeSpecies/LivingWithWildlife/- RaptorBufferGuidelines2008.pdf. Last accessed: May 2017.

Douglas County Board of Commissioners, El Paso County Board of Commissioners, Elbert County, Cherry Creek Soil Conservation District. 1960. Watershed Work Plan, Franktown-Parker Tributaries of Cherry Creek Watershed. Prepared with assistance from the US Department of Agriculture, Soil Conservation Service. April.

Douglas County Engineering. 2018. Dam Road Closure Evaluation, Technical Memorandum. December 3.

ERO Resources Corporation. 2015. Memorandum, Baldwin Gulch Dam – Summary of Natural Resources Assessment. Draft. November 19.

ERO Resources Corporation. 2017. Cultural Resource Survey for Franktown Parker Watershed Dam FP-B1 (Baldwin Gulch Dam), Douglas County, Colorado. Draft. July.

Federal Emergency Management Agency (FEMA). 2005. Flood Insurance Study, Douglas County, Colorado and Incorporated Areas. Flood Insurance Study No. 08035CV001A. September 30.

Federal Insurance Administration. 1999. Depth-Damage Curves.

Golder Associates Inc. (Golder). 2018a. Technical Memorandum, Baldwin Gulch (FP-B1) Dam Geotechnical Stability Evaluation. January 3.

Golder Associates Inc. (Golder). 2018b. Technical Memorandum, Hazard Classification Report on Franktown- Parker Watershed Dam FP-B1. Draft. January 22.

Howard, Needles, Tammen, & Bergendoff (HNTB). 1977. Flood Hazard Area Delineation for Happy Canyon Creek, Badger Gulch, Newlin Gulch, Baldwin Gulch, Sulphur Gulch, Tallman Gulch. November.

Kiowa Engineering Corporation. 1994. Newlin & Baldwin Gulches and basin 4600-09 Outfall Systems Planning Study Preliminary Design Report. December.

Muller Engineering Company, Inc. 2014. Franktown Parker – B1 Dam on Baldwin Gulch: Hazard Classification Report. Prepared for Urban Drainage and Flood Control District. November.

Natural Resources Conservation Service. 2005. “Earth Dams and Reservoirs (TR-60)”. U.S. Department of Agriculture, Conservation Engineering Division. July.

State of Colorado, Division of Water Resources (DWR). 2007. “Rules and Regulations for Dam Safety and Dam Construction, Department of Natural Resources, Division of Water Resources, Office of the State Engineer, Dam Safety Branch, January.

State of Colorado, Division of Water Resources (DWR). 2013. “Dam Safety Project Review Guide,” Division of Water Resources, April.

September 4, 2019 1911774-2000-3-R-3 Appendix D

State of Colorado, Division of Water Resources (DWR). 2016. Transmittal of Dam Safety Engineer’s Inspection Report (EIR), Franktown Parker FPB-1, DAMID: 080129, Water Division 1, Water District 8. Dam Safety Branch, Department of Natural Resources. Letter to Linda Pollick from John Hunyadi, PE, dated December 2.

U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). 1963. As-built drawings, Detention Dam FP-B1. April 16.

U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS). 2014. National Watershed Program Manual, April. Amended January 2015.

U.S. Department of Agriculture. 2014. “Soil Survey of Castle Rock Area, Colorado,” Natural Resources Conservation Service.

US Army Corps of Engineers (USACE). 1992. Catalog of Residential Depth-Damage Functions Used by the Army Corps of Engineers in Flood Damage Estimation, US Army Corp of Engineers Water Resources Support Center Institute for Water Resources, Fort Belvoir, Virginia. Authored by Stuart Davis and Leigh Skaggs. May.

US Department of Transportation (USDOT). 2018. Benefit-Cost Analysis Guidance for Discretionary Grant Programs. June.

Wilson & Company, Inc. (Wilson). 2016a. Memorandum, Franktown-Parker FP-B1 Watershed Planning Study Hydraulic Structures Conditions Assessment. March.

Wilson & Company, Inc. (Wilson). 2016b. Memorandum, Franktown-Parker FP-B1 Watershed Planning Study Hydrology Analysis. March.

Wilson & Company, Inc. (Wilson). 2016c. Memorandum, Franktown-Parker FP-B1 Watershed Planning Study Sediment Deposition Analysis. March.

Table

September 2019 Table D-11 19117764 Evaluation Matrix

Scoring Criteria * Operation and Implementation Feasibility of Public Construction Feasibility of Maintanence Total Costs Implementation Safety Risk Funding Issues Addtl. Roadway Alternative ID Rank Conveyance Addtl. Estimated Alternative 15% 20% 25% 20% 10% 10% 100% Approx. Initial Improvement Legal/Floodplain Annual O&M Benefit/Cost No. Capital Cost Costs Management Fees Cost Ratio B/C Rank * Scoring from 1 to 5 where 1 is the best option 1 No Action (Future Without Project) 4.0 5.0 5.0 2.0 4.0 1.0 3.8 7 $ 27,200,000 $ 250,000 $ 2,500 0.1 6 2 Decommissioning 4.0 4.5 5.0 2.0 4.0 1.0 3.7 6 $ 27,800,000 $ - $ 250,000 $ 2,500 0.1 7 3 Existing Spillway Modifications (Significant Hazard) 5.0 4.0 3.0 3.5 2.0 2.0 3.4 4 $ 25,700,000 $ - $ - $ 7,500 0.1 5 4 RCC Overtopping Protection 5.0 4.0 3.0 3.0 4.0 3.0 3.6 5 $ 7,000,000 $ - $ - $ 7,500 0.2 3 5 RCC (High Hazard) Spillway 2.0 2.0 1.0 1.0 2.0 2.0 1.6 1 $ 3,000,000 $ - $ - $ 5,000 0.6 1 6 RCC (Significant Hazard) Spillway and Floodproofing 5.0 4.0 3.0 1.0 4.0 2.5 3.2 3 $ 24,600,000 $ - $ - $ 7,500 0.1 4 7 New Principal and RCC Auxiliary Spillway 3.0 3.0 2.0 2.0 2.0 1.5 2.3 2 $ 3,200,000 $ - $ - $ 5,000 0.5 2

Figures

Path: \\Denver\acad\14\1420113\PRODUCTION\_A CULVERT SURVEY\Baldwin Gulch\Alternatives Report Figures\ | File Name: 1420113F001.dwg | Last Edited By: pacampbell Date: 2018-07-20 Time:12:46:59 PM | Printed By: NRosenthal Date: 2019-03-22 Time:12:26:16 PM DOUGLAS COUNTYENGINEERING CONSULTANT CLIENT REVIEWED PREPARED DESIGNED APPROVED YYYY-MM-DD SWR MBR CPB PFC 2018-01-15 BALDWIN GULCHWATERSHED DAMFP-B1 PROJECT NO. PROJECT TITLE 1420113 WATER SURFACE PROFILESFORTHE100-YR RECURRENCE WATERSHED PLANNINGSTUDY INTERVAL EVENT

REV. ---- FIGURE D8

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: ANSI B 0 1 in Path: \\Denver\acad\14\1420113\PRODUCTION\_A CULVERT SURVEY\Baldwin Gulch\Alternatives Report Figures\ | File Name: 1420113F002.dwg | Last Edited By: pacampbell Date: 2018-07-20 Time:12:51:26 PM | Printed By: NRosenthal Date: 2019-03-22 Time:12:27:29 PM DOUGLAS COUNTYENGINEERING CONSULTANT CLIENT REVIEWED PREPARED DESIGNED APPROVED YYYY-MM-DD SWR MBR CPB PFC 2018-05-14 BALDWIN GULCHWATERSHED DAMFP-B1 PROJECT NO. PROJECT TITLE 1420113 WATER SURFACE PROFILESFORTHE500-YR RECURRENCE WATERSHED PLANNINGSTUDY INTERVAL EVENT

REV. ---- FIGURE D9

REVIEWED PREPARED DESIGNED APPROVED YYYY-MM-DD SWR MBR CPB PFC 2018-05-14 BALDWIN GULCHWATERSHED DAMFP-B1 PROJECT NO. PROJECT 1420113 TITLE WATERSHED PLANNINGSTUDY WATER SURFACE PROFILESFORTHEPMP EVENT

REV. ----

D10 FIGURE

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: ANSI B 0 1 in LEGEND

BALDWIN GULCH DAM FP-B1

PARCEL BOUNDARIES

L UNINCORPORATED DAM BREACH INUNDATION EXTENT (GOLDER) B

T DOUGLAS COUNTY

S FEMA 100-YEAR FLOODPLAIN

E R

C ZONE AE

N W

O ZONE AE (FLOODWAY) R

C PINE LN

MEADOWGATE LN

S P AR K E R

R D

e D PONDEROSA DR e R r A

C N

S y r F r E e L h D C T

R D

N AVE P LINCOL E I

E E C R R E C E E K G A Feet T L O IL CENTENNIAL DR P V 0 400 800 1,600 A V E REFERENCE 1. AERIAL IMAGERY: NATIONAL AGRICULTURE IMAGERY PROGRAM, USDA. IMAGE CAPTURED NOVEMBER 2015. 2. PARCEL BOUNDARIES: DOUGLAS COUNTY ASSESSOR'S OFFICE. TWENTY MILE RD SAGEBRUSH DR

CLIENT TOWN OF PARKER DOUGLAS COUNTY ENGINEERING

HOMESTEAD RD PROJECT BALDWIN GULCH DAM FP-B1 SUPPLEMENTAL WATERSHED PLAN

TITLE GOLDER DAM BREACH INUNDATION EXTENT AND FEMA 100-YEAR FLOODPLAIN IF IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM: CONSULTANT YYYY-MM-DD 2018-05-21 in1 PREPARED KJC

DESIGN KJC PLAZA DR REVIEW CB APPROVED SR PROJECT No. FIGURE 1420113

Path: M:\BaldwinGulch\Mapping\201804\11x17_BaldwinGulch_FigD10_InundationComparisons.mxd D11 0 LEGEND UNINCORPORATED DAM DOUGLAS COUNTY 100-YEAR FLOODPLAIN (WITH DAM)

100-YEAR FLOODPLAIN (WITHOUT DAM)

PARCEL BOUNDARY CROWN CREST BLVD CREST CROWN INUNDATED PROPERTIES (DAM) PINE LN INUNDATED PROPERTIES (WITHOUT DAM)

)" STRUCTURE LOCATION

MEADOWGATE LN

S PARKER RD

D OSA DR R PONDER A

R D

LN AVE E LINCO )" )" P I N

D )"

R Y

W )" )"

K E

C E R

E R E C )" K E )" T G Feet O A L 0 375 750 1,500 P IL CENTENNIAL DR A V V E REFERENCE 1. AERIAL IMAGERY: NATIONAL AGRICULTURE IMAGERY PROGRAM, USDA. IMAGE CAPTURED NOVEMBER 2015. 2. PROPERTY OWNERSHIP DATASET: DOUGLAS COUNTY ASSESSOR'S OFFICE. SAGEBRUSH DR 3. ELEVATION DATA: CONTOURS DERIVED FROM NATIONAL ELEVATION DATASET (NED), USGS.

TWENTY MILE RD CLIENT TOWN OF PARKER DOUGLAS COUNTY

HOMESTEAD RD PROJECT BALDWIN GULCH DAM FP-B1

TITLE 100-YEAR FLOODPLAIN EXTENTS WITH AND WITHOUT DAM IF IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM: CONSULTANT YYYY-MM-DD 2017-04-24 in1 PREPARED KJC

DESIGN KJC REVIEW CB PLAZA DR APPROVED SR PROJECT No. FIGURE 1420113

Path: M:\BaldwinGulch\Mapping\11x17_BaldwinGulch_Fig1_100yrExtents.mxd D12 0 Path: \\Denver.golder.gds\acad\14\1420113\PRODUCTION\_B Economic Evaluations\ | File Name: 1420113B001.dwg DOUGLAS COUNTY CONSULTANT CLIENT CONSULTANT CLIENT REVIEWED PREPARED DESIGNED REVIEWED PREPARED DESIGNED APPROVED YYYY-MM-DD APPROVED YYYY-MM-DD SWR PFC CPB CPB 2017-04-24 100-YEAR STORM EVENTDAM/NODAMWATER SURFACE BALDWIN GULCHDAMFP-B1 ECONOMIC EVALUATIONS REPORT PROJECT NO. PROJECT PROJECT NO. PROJECT TITLE 1420113 TITLE PROFILES

REV. REV. A FIGURE D13

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: ANSI B 0 1 in Path: \\Denver.golder.gds\acad\14\1420113\PRODUCTION\_B Economic Evaluations\ | File Name: 1420113B002.dwg DOUGLAS COUNTY CONSULTANT CLIENT REVIEWED PREPARED DESIGNED APPROVED YYYY-MM-DD SWR PFC CPB CPB 2017-04-24 BALDWIN GULCHDAMFP-B1 ECONOMIC EVALUATIONS REPORT PROJECT NO. PROJECT 500-YEAR STORM EVENTDAM/NODAMWATER SURFACE TITLE 1420113 PROFILES REV. A FIGURE D14

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: ANSI B 0 1 in C R LEGEND O

N 500-YEAR FLOODPLAIN (PROPOSED DESIGN)

E 500-YEAR FLOODPLAIN (EXISTING)

L PARCEL BOUNDARIES (EXISTING)

D UNINCORPORATED DOUGLAS COUNTY

PINE LN

MEADOWGATE LN

S P AR K E R

R D

D R PONDEROSA DR A N

LN AVE E LINCO

P I N

Feet 0 350 700 1,400

REFERENCE Y

W 1. AERIAL IMAGERY: NATIONAL AGRICULTURE IMAGERY PROGRAM, USDA.

K 2. PARCEL BOUNDARIES: DOUGLAS COUNTY ASSESSOR'S OFFICE, 2016.

P K

E E C R R C E E CLIENT E G K A L T DOUGLAS COUNTY ENGINEERING IL CENTENNIAL DR O V P A V E PROJECT BALDWIN GULCH DAM FP-B1 SUPPLEMENTAL WATERSHED PLAN TWENTY MILE RD SAGEBRUSH DR TITLE 500-YEAR FLOODPLAIN EXTENTS EXISTING AND PROPOSED REHABILITATION ALTERNATIVE

TOWN OF PARKER IF THISMEASUREMENT DOES NOT MATCH WHATIS SHOWN, THE SHEET SIZEHAS BEEN MODIFIED FROM: CONSULTANT YYYY-MM-DD 2019-04-15 in1 PREPARED KJC

HOMESTEAD RD DESIGN KJC REVIEW MB

APPROVED CB PROJECT No. FIGURE 19117764

Path: M:\BaldwinGulch\Mapping\201904\11x17_BaldwinGulch_FigureD15.mxd D15 0 Figure D16 Estimated Benefits per Event FB-B1 Supplemental Watershed Plan

$1,800,000

$1,600,000

$1,400,000

$1,200,000

$1,000,000 Damages/Benefits

$800,000 Incremental

$600,000 Estiamted

$400,000

$200,000

$0 500‐year Event 100‐year Event 50‐year Event 10‐year Event 5‐year Event 2‐year Event Probability of Occurrence

ATTACHMENT D-1 Alternatives Cost Estimate Summary

September 2019 19117764

No Alternative Estimated Cost Rank 1 No Action/Future Without Project $27,200,000 6 2 Decommissioning $27,800,000 7 3 Spillway Widening/Lowering + Flood Proofing (Significant) $25,700,000 5 4 RCC Overtopping $7,000,000 3 5 RCC Spillway (High) $3,000,000 1 6 RCC Spillway + Flood Proofing (Significant) $24,600,000 4 7 RCC Spillway + Principal Spillway Replacement $3,200,000 2 September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 1 - No Action (Future without Project) ESTIMATED S. Rogers DATE: 3/15/2019 Alternative BY: UNIT TOTAL NO DESCRIPTION QUANTITY UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $40,000.00 $40,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $5,000.00 $5,000 5 Earthwork 5a Excavation (Embankment) 32,700 cubic yards $6.00 $196,200 5b Riprap 1,300 cubic yards $65.00 $84,500 6 Principal Spillway Decommissioning 1 lump sum $15,000.00 $15,000 7 Reclamation and Seeding 2 acres $8,500.00 $17,000 8 Instrumentation and Monitoring 1 lump sum $6,000.00 $6,000 9 Downstream Floodproofing 1 lump sum $ 10,000.00 $10,000 10 Roadway Crossing Improvements 10a Pine Drive 1 lump sum $ 319,000 $319,000 10b Lincoln Avenue 1 lump sum $ 495,000 $495,000 10c Parker Road 1 lump sum $ 1,562,000 $1,562,000 9 Unlisted Items (10%) $32,000 Construction Cost Subtotal $2,806,700 Contingency (25%) $701,700 Engineering (8%) $224,500 Constr. Oversight, QA/QC Testing, As-builts (5%) $140,300 Permitting $60,000 Land Acquisition $23,223,200 Legal/Project Administration $40,000 Total Estimated Costs $27,196,400 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 2 - Decommissioning Alternative ESTIMATED S. Rogers DATE: 3/15/2019 BY: UNIT TOTAL NO DESCRIPTION QUANTITY UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $50,000.00 $90,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Embankment) 32,700 cubic yards $6.00 $196,200 5b Exisiting Spillway Re-grading 19,600 cubic yards $3.50 $68,600 5c Riprap 1,500 cubic yards $65.00 $97,500 6 Principal Spillway Modifications (Water Quality) 1 lump sum $20,000.00 $20,000 7 Reclamation 7a Reclamation and Seeding (Wetlands) 2 acres $15,000.00 $30,000 7b Reclamation and Seeding (Grasses) 2 acres $6,500.00 $13,000 8 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 9 Downstream Floodproofing 1 lump sum $ 26,200.00 $26,200 10 Roadway Crossing Improvements 10a Pine Drive 1 lump sum $ 319,000 $319,000 10b Lincoln Avenue 1 lump sum $ 495,000 $495,000 10c Parker Road 1 lump sum $ 1,562,000 $1,562,000 11 Unlisted Items (10%) $284,000 Construction Cost Subtotal $3,246,500 Contingency (25%) $811,600 Engineering (3%) $97,400 Constr. Oversight, QA/QC Testing, As-builts (5%) $162,300 Permitting $100,000 Land Acquisition $23,223,200 Legal/Project Administration $100,000 Total Estimated Costs $27,741,000 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 3 - Auxiliary Spillway Widening/Lowering ESTIMATED S. Rogers DATE: 3/15/2019 Alternative (160 ft) BY: UNIT TOTAL NO DESCRIPTION QUANTITY UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $90,000.00 $160,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Auxiliary Spillway) 12,400 cubic yards $6.00 $74,400 5b Excavation (Principal Spllway) 7,500 cubic yards $6.00 $45,000 5c Riprap 700 cubic yards $65.00 $45,500 6 Principal Spillway Replacement 6a Reinforced Concrete Tower 30 cubic yards $750.00 $22,500 6b 30-inch Steel Outlet Conduit 210 linear feet $500.00 $105,000 6c Steel Pipe Concrete Encasement 90 cubic yards $600.00 $54,000 6d Filter Diaphragm 10 cubic yards $75.00 $750 6e Trash Racks and Metal Work 1 lump sum $30,000.00 $30,000 7 Reinforced Concrete Auxiliary Spillway 7a Concrete Spillway Weir 80 cubic yards $750.00 $60,000 7b Concrete Training Walls 140 cubic yards $750.00 $105,000 7c Concrete Floor 1,260 cubic yards $600.00 $756,000 8 Reclamation and Seeding 2 acres $6,500.00 $13,000 9 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 10 Downstream Flood Proofing 1 lump sum $ 30,000.00 $30,000 11 Unlisted Items (10%) $132,000 Construction Cost Subtotal $1,678,150 Contingency (25%) $419,500 Engineering (12%) $201,400 Constr. Oversight, QA/QC Testing, As-builts (5%) $83,900 Permitting $40,000 Land Acquisition $23,223,200 Legal/Project Administration $50,000 Total Estimated Costs $25,696,150 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 4 - RCC Overtopping Alternative ESTIMATED S. Rogers DATE: 3/15/2019 BY: TOTAL NO DESCRIPTION QUANTITY UNIT UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $250,000.00 $250,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Embankment) 15,500 cubic yards $6.00 $93,000 5b Excavation (Principal Spillway) 7,500 cubic yards $6.00 $45,000 5b Excavation (Apron) 7,600 cubic yards $6.00 $45,600 5c Riprap 2,600 cubic yards $65.00 $169,000 5d RCC Topsoil Cover 8,700 cubic yards $35.00 $304,500 6 Principal Spillway Replacement 6a Reinforced Concrete Tower 30 cubic yards $750.00 $22,500 6b 30-inch Steel Outlet Conduit 210 linear feet $500.00 $105,000 6c Steel Pipe Concrete Encasement 90 cubic yards $600.00 $54,000 6d Filter Diaphragm 10 cubic yards $75.00 $750 6e Trash Racks and Metal Work 1 lump sum $30,000.00 $30,000 7 RCC Overtopping Protection 7a RCC Overtopping 16,600 cubic yards $150.00 $2,490,000 7b RCC Apron 3,300 cubic yards $150.00 $495,000 7c Reinforced Concrete Cutoff Walls 560 cubic yards $450.00 $252,000 8 Existing Auxiliary Spillway Cutoff Wall 30 cubic yards $450.00 $13,500 9 Reclamation and Seeding 3 acres $6,500.00 $19,500 10 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 11 Unlisted Items (10%) $415,000 Construction Cost Subtotal $4,849,350 Contingency (25%) $1,212,300 Engineering (6%) $291,000 Constr. Oversight, QA/QC Testing, As-builts (10%) $484,900 Permitting $40,000 Legal/Project Administration $50,000 Total Estimated Costs $6,927,550 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 5 - RCC Spillway Alternative - 400 ft ESTIMATED S. Rogers DATE: 3/15/2019 (High Hazard) BY: TOTAL NO DESCRIPTION QUANTITY UNIT UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $120,000.00 $160,000 2 Erosion Control Plan and Construction Permits 1 lump sum $12,500.00 $12,500 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Embankment) 10,340 cubic yards $6.00 $62,040 5b Excavation (Principal Spillway) 7,500 cubic yards $6.00 $45,000 5c Excavation (Apron) 2,625 cubic yards $6.00 $15,750 5d Existing Auxiliary Spillway Re-grading 19,600 cubic yards $3.50 $68,600 5e Riprap 810 cubic yards $65.00 $52,650 6 Principal Spillway Replacement 6a Reinforced Concrete Tower 30 cubic yards $750.00 $22,500 6b 30-inch Steel Outlet Conduit 210 linear feet $500.00 $105,000 6c Steel Pipe Concrete Encasement 90 cubic yards $600.00 $54,000 6d Filter Diaphragm 10 cubic yards $75.00 $750 6e Trash Racks and Metal Work 1 lump sum $30,000.00 $30,000 7 RCC Auxiliary Spillway 7a RCC 4,440 cubic yards $150.00 $666,000 7b Concrete Walls 70 cubic yards $750.00 $52,500 7c Cutoff/Low Flow Channel Walls 175 cubic yards $450.00 $78,750 7d RCC Topsoil Cover 4,040 cubic yards $35.00 $141,400 8 Reclamation and Seeding 5.0 acres $6,500.00 $32,500 9 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 10 Upstream Floodproofing 1 lump sum $ 170,300.00 $170,300 11 Unlisted Items (10%) $161,000 Construction Cost Subtotal $1,961,240 Contingency (25%) $490,300 Engineering (15%) $294,200 Constr. Oversight, QA/QC Testing, As-builts (8%) $156,900 Permitting $40,000 Legal/Project Administration $50,000 Total Estimated Costs $2,992,600 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 6 - RCC Spillway Alternative - 160 ft ESTIMATED S. Rogers DATE: 6/13/2017 (Significant Hazard) BY: UNIT TOTAL NO DESCRIPTION QUANTITY UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $120,000.00 $120,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Embankment) 2,910 cubic yards $6.00 $17,460 5b Excavation (Apron) 755 cubic yards $6.00 $4,530 5c Riprap 235 cubic yards $65.00 $15,275 6 Principal Spillway Replacement 6a Reinforced Concrete Tower 30 cubic yards $750.00 $22,500 6b 30-inch Steel Outlet Conduit 210 linear feet $500.00 $105,000 6c Steel Pipe Concrete Encasement 90 cubic yards $600.00 $54,000 6d Filter Diaphragm 10 cubic yards $75.00 $750 6e Trash Racks and Metal Work 1 lump sum $30,000.00 $30,000 7 RCC Auxiliary Spillway 7a RCC 1,000 cubic yards $150.00 $150,000 7b Concrete Walls 70 cubic yards $750.00 $52,500 7c Cutoff/Low Flow Channel Walls 50 cubic yards $450.00 $22,500 7d RCC Topsoil Cover 1,160 cubic yards $35.00 $40,600 8 Exisiting Auxiliary Spillway Concrete Cutoff Wall 30 cubic yards $450.00 $13,500 9 Reclamation and Seeding 4.0 acres $6,500.00 $26,000 10 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 11 Downstream Floodproofing 1 lump sum $ 30,000.00 $30,000 12 Unlisted Items (10%) $56,000 Construction Cost Subtotal $805,615 Contingency (25%) $201,400 Engineering (18%) $145,000 Constr. Oversight, QA/QC Testing, As-builts (10%) $80,600 Permitting $40,000 Land Acquisition $23,223,200 Legal/Project Administration $50,000 Total Estimated Costs $24,545,800 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated. September 2019 19117764

COST ESTIMATE PROJECT: Baldwin Gulch FP-B1 Watershed Planning Study DESIGN Conceptual PROJECT NO: 1420113 LEVEL: ITEM: Alternative No. 7 - RCC Spillway Alternative - 420 ft and ESTIMATED S. Rogers DATE: 6/13/2017 New Principal Spillway BY: TOTAL NO DESCRIPTION QUANTITY UNIT UNIT COST COST 1 Mobilization/De-mobilization 1 lump sum $120,000.00 $190,000 2 Erosion Control Plan and Construction Permits 1 lump sum $15,000.00 $15,000 3 Dewatering/Diversion 1 lump sum $10,000.00 $10,000 4 Erosion Control 1 lump sum $10,000.00 $10,000 5 Earthwork 5a Excavation (Embankment) 9,240 cubic yards $6.00 $55,440 5b Excavation (Principal Spillway) 7,500 cubic yards $6.00 $45,000 5c Excavation (Apron) 2,345 cubic yards $6.00 $14,070 5d Existing Spillway Re-grading 19,600 cubic yards $3.50 $68,600 5e Riprap 2,800 cubic yards $65.00 $182,000 6 Principal Spillway Replacement 6a Reinforced Concrete Tower 35 cubic yards $750.00 $26,250 6b 12 ft x 5 ft RCBC 140 linear feet $1,200.00 $168,000 6c Filter Diaphragm 20 cubic yards $75.00 $1,500 6d Trash Racks and Metal Work 1 lump sum $35,000.00 $35,000 7 RCC Auxiliary Spillway 7a RCC 3,800 cubic yards $150.00 $570,000 7b Concrete Walls 300 cubic yards $750.00 $225,000 7c Cutoff/Low Flow Channel Walls 80 cubic yards $450.00 $36,000 7d RCC Topsoil Cover 3,610 cubic yards $35.00 $126,350 8 Reclamation and Seeding 5.0 acres $6,500.00 $32,500 9 Instrumentation and Monitoring 1 lump sum $10,000.00 $10,000 10 Upstream Floodproofing 1 lump sum $ 170,300.00 $170,300 11 Unlisted Items (10%) $177,000 Construction Cost Subtotal $2,168,010 Contingency (25%) $542,000 Engineering (10%) $216,800 Constr. Oversight, QA/QC Testing, As-builts (5%) $108,400 Permitting $40,000 Legal/Project Administration $50,000 Total Estimated Costs $3,125,200 1. Preliminary cost estimate developed using unit rates from other similar projects in the Northern Colorado. Final cost Notes: estimate will be updated based on final design. 2. Dewatering/diversion assumes that irrigation flows will need to be maintained during construction. 3. Construction Oversight, QA/QC Testing, as-built documentation, permitting and legal fees are estimated.

ATTACHMENT D-2 Summary of Damage Estimates

September 2019 Assessor's Data 19117764

PRIMARY TOTAL TOTAL PRIMARY PRIMARY PROPERTY PRIMARY PRIMARY PRIMARY STATE PARCEL ACCOUNT ACCOUNT ACTUAL ASSESSED TOTAL PRIMARY PROPERTY PROPERTY PROPERTY STREET PROPERTY PRIMARY PROPERTY STREET PRIMARY PROPERTY OWNER MAILING PRIMARY OWNER OWNER OWNER NUMBER NUMBER TYPE LEGAL DESCRIPTION VALUE VALUE ACRES STREET NAME CITY ZIPCODE NUMBER SUFFIX ADDRESS ADDRESS1 CITY STATE ZIPCODE OWNER NAME 2233-142-08-006 R0451895 Exempt MOST TRACT B STROH EXEMPTION PLAT 17.789 AM/L$ 225,000 $ 65,250 17.789 PINE PARKER 80134 11944 DR 11944 PINE DR PO BOX 1030 PARKER CO 80134 GRACE BAPTIST CHURH OF PARKER INC 2233-142-99-016 R0482298 Exempt PART PARCEL B STROH EXEMPTION 0.181 AM/L$ 217 $ 60 0.181 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-142-99-010 R0409717 Exempt STREETS IN CENTENNIAL RANCH AKA PINE DR CENTENNIAL DR; JAKE'S RANCH$ - $ - 6.37 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-01-011 R0409754 Residential LOT 19 CENTENNIAL RANCH 2.74 AM/L$ 1,965,592 $ 156,460 2.74 JAKES RANCH PARKER 801380000 11935 RD 11935 JAKES RANCH RD 11935 JAKES RANCH RD PARKER CO 801380000 RICHARD JENNINGS & LESLEY JENNINGS 2233-140-01-019 R0409764 Residential LOT 27 CENTENNIAL RANCH 3.45 AM/L$ 942,423 $ 75,020 3.45 CENTENNIAL PARKER 80138 7330 DR 7330 CENTENNIAL DR 7330 CENNTENNIAL DR PARKER CO 80138 JOHN J HUMPHRIES 2233-140-01-010 R0409753 Residential LOT 18 CENTENNIAL RANCH 5.05 AM/L$ 2,539,802 $ 202,170 5.05 CENTENNIAL PARKER 731031503 7251 DR 7251 CENTENNIAL DR 435 NW 22ND ST OKLAHOMA CITY OK 731031503 SOLID ROCK TRUST 2233-140-01-012 R0409755 Residential LOT 20 CENTENNIAL RANCH 2.48 AM/L$ 1,390,662 $ 110,700 2.48 JAKES RANCH PARKER 801388739 11965 RD 11965 JAKES RANCH RD 11965 JAKES RANCH RD PARKER CO 801388739 DAVID BOYER & MICHELLE BOYER 2233-140-01-018 R0409725 HOA TRACT D CENTENNIAL RANCH 2.12 AM/L$ - $ - 2.12 None 80134 None None M&M PROPERTY MANAGEMENT PARKER CO 80134 CENTENNIAL RANCH HOMEOWNERS ASSOCIATION 2233-140-01-015 R0409759 Residential LOT 23 CENTENNIAL RANCH 2.30 AM/L$ 862,645 $ 68,670 2.3 CENTENNIAL PARKER 801388737 7425 DR 7425 CENTENNIAL DR 7425 CENTENNIAL DR PARKER CO 801388737 ROBERT B MILLER 2233-140-01-017 R0409761 Residential LOT 25 CENTENNIAL RANCH 2.88 AM/L$ 1,031,090 $ 82,070 2.88 CENTENNIAL PARKER 80138 7410 DR 7410 CENTENNIAL DR 7410 CENTENNIAL DR PARKER CO 80138 BRENT J GALE & LUCY M GALE 2233-140-01-021 R0409723 HOA TRACT B CENTENNIAL RANCH 35.08 AM/L$ - $ - 35.08 None 80138 None None 7438 CENTENNIAL DR PARKER CO 80138 CENTENNIAL RANCH HOMEOWNERS ASSOCIATION 2233-140-01-042 R0436923 Vacant Land TRACT D HOMESTEAD HILLS FLG 3 13.4 AM/L$ 231,000 $ 66,990 13.4 PONDEROSA PARKER 801349560 7695 LN 7695 PONDEROSA LN 16012 PARKSIDE DR PARKER CO 801349560 GREGORY J BALDWIN & JENNIFER T BALDWIN 2233-140-01-041 R0436922 Residential TRACT C HOMESTED HILLS FLG 3 12.78 AM/L$ 631,348 $ 50,260 12.78 PONDEROSA PARKER 801388629 7687 LN 7687 PONDEROSA LN 13661 N TRAVOIS TRL PARKER CO 801388629 EAST PONDEROSA LLC 2233-140-01-016 R0409760 Residential LOT 24 CENTENNIAL RANCH 3.31 AM/L$ 1,480,973 $ 117,890 3.31 CENTENNIAL PARKER 80138 7438 DR 7438 CENTENNIAL DR 7438 CENTENNIAL DR PARKER CO 80138 STEVEN A BUDNACK 2233-140-01-020 R0409762 Residential LOT 26 CENTENNIAL RANCH 3.83 AM/L$ 1,068,624 $ 85,060 3.83 CENTENNIAL PARKER 80134 7290 DR 7290 CENTENNIAL DR 7290 CENTENNIAL DR PARKER CO 80134 BEVERLY J CRAVEN & E RANDY CRAVEN 2233-140-01-014 R0409758 Residential LOT 22 CENTENNIAL RANCH 2.48 AM/L$ 943,723 $ 75,120 2.48 CENTENNIAL PARKER 801380000 7311 DR 7311 CENTENNIAL DR 7311 CENTENNIAL DR PARKER CO 801380000 JOHN F PEISNER & PAMELA J PEISNER 2233-140-01-013 R0409756 Residential LOT 21 CENTENNIAL RANCH 2.30 AM/L$ 1,563,864 $ 124,480 2.3 JAKES RANCH PARKER 801388738 11950 RD 11950 JAKES RANCH RD 11950 JAKES RANCH RD PARKER CO 801388738 KENNETH H EWING 2233-140-01-004 R0095791 Residential TRACT 1 HOMESTEAD HILLS 3 TOTAL ACREAGE 8.08 AM/L$ 455,127 $ 36,230 8.08 PONDEROSA PARKER 801380000 7769 LN 7769 PONDEROSA LN 7769 PONDEROSA LN PARKER CO 801380000 JAMES R DUDLEY JR 2233-142-99-017 R0482299 Exempt PART PARCEL B STROH EXEMPTION 1.638 AM/L$ 1,966 $ 570 1.638 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-07-036 R0436725 Residential MOST OF LOT 1 PARKER HILLS ESTATES TOTAL ACREAGE 4.633 AM/L$ 460,765 $ 36,680 4.633 BALDWIN GULCH PARKER 80138 7053 CIR 7053 BALDWIN GULCH CIR 7053 BALDWIN GULCH CIR PARKER CO 80138 GERALD LEE RIEDEL 2233-142-01-037 R0438449 Vacant Land MOST OF LOT 11 CENTENNIAL RANCH 3.171 AM/L$ 325,000 $ 94,250 3.171 SAGEBRUSH PARKER 801385500 7150 DR 7150 SAGEBRUSH DR 3452 MEADOWLARK CT PARKER CO 801385500 BARTON J KELLOGG & JENNIFER R KELLOGG 2233-142-01-040 R0436858 Residential MOST OF LOT 10 CENTENNIAL RANCH 14-6-66 TOTAL ACREAGE 3.440 AM/L$ 1,392,277 $ 110,830 3.44 WARRINGTON PARKER 801388735 11621 CT 11621 WARRINGTON CT 11621 WARRINGTON CT PARKER CO 801388735 MICHAEL S BLANDINA & DIANE M BLANDINA 2233-143-99-018 R0475121 Exempt ROW PARKER HILLS ESTATES 1.832 AM/L$ - $ - 1.832 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-142-01-041 R0436854 Residential MOST OF LOT 9 CENTENNIAL RANCH TOTAL ACREAGE 3.356 AM/L$ 1,391,470 $ 110,760 3.356 WARRINGTON PARKER 801380000 11561 CT 11561 WARRINGTON CT 11561 WARRINGTON CT PARKER CO 801380000 FRANCIS LANG & BARBARA LANG 2233-142-08-005 R0451897 Residential PART TRACT B STROH EXEMPTION PLAT 4.311 AM/L$ 832,269 $ 66,250 4.311 CENTENNIAL PARKER 801387214 7125 DR 7125 CENTENNIAL DR 7125 CENTENNIAL DR PARKER CO 801387214 ALEJANDRO J KOFFMANN & JAMIE MARIE KOFFMANN 2233-142-01-042 R0438014 Residential MOST LOT 8 CENTENNIAL RANCH 3.506 AM/L$ 1,039,737 $ 82,760 3.506 WARRINGTON PARKER 80138 11541 CT 11541 WARRINGTON CT 11541 WARRINGTON CT PARKER CO 80138 GREG LEWICKI 2233-142-01-039 R0436727 Residential MOST OF LOT 12 CENTENNIAL RANCH TOTAL ACREAGE 3.121 AM/L$ 1,130,451 $ 89,980 3.121 SAGEBRUSH PARKER 801380000 7120 DR 7120 SAGEBRUSH DR 7120 SAGEBRUSH DR PARKER CO 801380000 ROBERT KENNAH & CRYSTAL KENNAH 2233-143-99-010 R0446315 Exempt ROW NORTH EDGE SW1/4 14-6-66 PT HOMESTEAD HILLS RD$ - $ - 0 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-142-08-003 R0436852 HOA MOST OF TRACT C CENTENNIAL RANCH TOTAL ACREAGE 0.347 AM/L$ - $ - 0.347 None 80138 None None 7438 CENTENNIAL DR PARKER CO 80138 CENTENNIAL RANCH HOMEOWNERS ASSOCIATION 2233-140-07-004 R0232645 Residential LOT 11 PANORAMA AMENDED 4.753 AM/L 391-1002$ 446,935 $ 35,580 4.753 PANORAMA PARKER 80138 11480 CT 11480 N PANORAMA CT 11480 N PANORAMA CT PARKER CO 80138 MICHAEL J DOHERTY & BARBARA A DOHERTY 2233-140-03-007 R0100351 Residential LOT 1 PINE VALLEY 2.062 AM/L$ 510,427 $ 40,630 2.062 ROBIN PARKER 80138 7621 RD 7621 ROBIN RD 7621 E ROBIN RD PARKER CO 80138 ALLEN V BRUNO & KATHERINE L BRUNO 2233-140-01-022 R0409747 Residential LOT 13 CENTENNIAL RANCH 2.75 AM/L$ 1,004,293 $ 79,940 2.75 SAGEBRUSH PARKER 801388734 7145 DR 7145 SAGEBRUSH DR 7145 SAGEBRUSH DR PARKER CO 801388734 MICHAEL KELLY LIVING TRUST 2233-140-07-033 R0093921 Residential LOT 3 PARKER HILLS ESTS 5 AM/L$ 741,237 $ 59,010 5 HOMESTEAD PARKER 801380000 7210 RD 7210 HOMESTEAD RD 7210 HOMESTEAD RD PARKER CO 801380000 ROBERT W KNEPPER & KANDY J KNEPPER 2233-140-01-024 R0409749 Residential LOT 15 CENTENNIAL RANCH 2.39 AM/L$ 777,632 $ 61,900 2.39 SAGEBRUSH PARKER 80138 7255 DR 7255 SAGEBRUSH DR 7255 SAGEBRUSH DR PARKER CO 80138 DAVID EDWARDS & MELISSA A EDWARDS 2233-140-01-031 R0409739 Residential LOT 5 CENTENNIAL RANCH 3.63 AM/L$ 961,875 $ 76,570 3.63 SAGEBRUSH PARKER 801388733 7270 DR 7270 SAGEBRUSH DR 7270 SAGEBRUSH DR PARKER CO 801388733 GREENLEY FAMILY TRUST 2233-141-99-001 R0446309 Exempt ROW HOMESTEAD HILLS 3$ - $ - 0 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-01-009 R0409722 Exempt TRACT A CENTENNIAL RANCH 4.78 AM/L$ 28,680 $ 8,320 4.78 None 80138 None None 19801 E MAINSTREET PARKER CO 80138 PARKER WATER & SANITATION DISTRICT 2233-140-01-028 R0409726 Residential LOT 1 CENTENNIAL RANCH 3.60 AM/L$ 1,049,648 $ 83,550 3.6 SAGEBRUSH PARKER 801388740 7405 DR 7405 SAGEBRUSH DR 7405 SAGEBRUSH DR PARKER CO 801388740 KYUNG WON SHIN 2233-140-01-006 R0332977 Residential LOT 1 HOMESTEAD HILLS 1 AMENDED 4.83 AM/L$ 746,868 $ 59,450 4.83 PONDEROSA PARKER 801380000 7641 LN 7641 PONDEROSA LN 7641 PONDEROSA LN PARKER CO 801380000 PAULA ANN FREDERICKSEN 2233-140-07-032 R0232549 Residential LOT 1 PANORAMA AMENDED 4.847 AM/L 409-377$ 640,032 $ 50,950 4.847 PANORAMA PARKER 801387938 11491 CT 11491 N PANORAMA CT 11491 PANORAMA CT PARKER CO 801387938 KENNETH A RAMEY & LISA R RAMEY 2233-140-03-006 R0093471 Vacant Land TRACT 67 HOMESTEAD HILLS 1 TOTAL ACREAGE 8.31 AM/L$ 210,000 $ 60,900 8.31 HOMESTEAD PARKER 800141717 7576 RD 7576 HOMESTEAD RD 2392 S KENTON ST DENVER CO 800141717 R E DEVLIN & CO 2233-132-99-002 R0446306 Exempt ROW HOMESTEAD HILLS 1$ - $ - 0 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-01-033 R0409741 Residential LOT 7 CENTENNIAL RANCH 3.80 AM/L$ 1,475,310 $ 117,430 3.8 WARRINGTON PARKER 801388735 11562 CT 11562 WARRINGTON CT 11562 WARRINGTON CT PARKER CO 801388735 THOMAS MCCANN 2233-143-99-011 R0446316 Exempt ROW PANORAMA AMENDED SW1/4 14-6-66 PANORAMA CT$ - $ - 0 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-07-034 R0100431 Residential LOT 2 PARKER HILLS EST 5 AM/L 323-518$ 437,282 $ 34,810 5 HOMESTEAD PARKER 801387914 7152 RD 7152 HOMESTEAD RD 7152 HOMESTEAD RD PARKER CO 801387914 RICHARD D SKALECKE & BERNADINE E SKALECKE 2233-140-01-023 R0409748 Residential LOT 14 CENTENNIAL RANCH 2.39 AM/L$ 1,001,732 $ 79,740 2.39 SAGEBRUSH PARKER 80138 7205 DR 7205 SAGEBRUSH DR 7205 SAGEBRUSH DR PARKER CO 80138 BRIGITTE A STEEGHS 2233-140-01-030 R0409736 Residential LOT 4 CENTENNIAL RANCH 3.630 AM/L$ 916,493 $ 72,950 3.63 SAGEBRUSH PARKER 80138 7300 DR 7300 SAGEBRUSH DR 7300 SAGEBRUSH DR PARKER CO 80138 LUTHER HUNNINGS & MELINDA HUNNINGS 2233-140-01-025 R0409751 Residential LOT 16 CENTENNIAL RANCH 2.39 AM/L$ 848,478 $ 67,540 2.39 SAGEBRUSH PARKER 801388734 7285 DR 7285 SAGEBRUSH DR 7285 SAGEBRUSH DR PARKER CO 801388734 CYNTHIA R HASKELL & RICK HASKELL 2233-140-01-026 R0409752 Residential LOT 17 CENTENNIAL RANCH 2.93 AM/L$ 930,352 $ 74,060 2.93 SAGEBRUSH PARKER 80138 7315 DR 7315 SAGEBRUSH DR 7315 SAGEBRUSH DR PARKER CO 80138 FAWAZ FAMILY TRUST ETAL 2233-140-01-029 R0409734 Residential LOT 3 CENTENNIAL RANCH 4.10 AM/L$ 2,472,000 $ 196,770 4.1 SAGEBRUSH PARKER 80138 7390 DR 7390 SAGEBRUSH DR 7390 SAGEBRUSH DR PARKER CO 80138 COLLEEN F PISCIOTTA 2233-140-01-027 R0409729 Residential LOT 2 CENTENNIAL RANCH 3.52 AM/L$ 2,261,616 $ 180,020 3.52 SAGEBRUSH PARKER 801388734 7375 DR 7375 SAGEBRUSH DR 7375 SAGEBRUSH DR PARKER CO 801388734 VINAY K SIKKA & ANITA SIKKA 2233-140-07-003 R0105312 Residential LOT 32 PINE VALLEY 2.76 AM/L$ 363,573 $ 28,940 2.76 ROBIN PARKER 801380000 7530 RD 7530 ROBIN RD 7530 E ROBIN RD PARKER CO 801380000 MARVIN LYNN MITCHELL & PAULA HINES MITCHELL 2233-140-01-032 R0409740 Residential LOT 6 CENTENNIAL RANCH 3.62 AM/L$ 1,039,635 $ 82,750 3.62 SAGEBRUSH PARKER 801380000 7240 DR 7240 SAGEBRUSH DR 7240 SAGEBRUSH DR PARKER CO 801380000 MARTIN D SHEA & LILIAN SHEA 2233-140-01-040 R0436921 Residential TRACT B HOMESTEAD HILLS FLG 3 8.52 AM/L$ 504,887 $ 51,260 8.52 PONDEROSA PARKER 80138 7665 LN 7665 PONDEROSA LN 7665 E PONDEROSA LN PARKER CO 80138 KELLY G ELLINGSON KATHERINE H ELLINGSON 2233-140-01-007 R0332978 Residential LOT 2 HOMESTEAD HILLS 1 AMENDED 4.83 AM/L$ 1,370,230 $ 109,070 4.83 PONDEROSA PARKER 80126 7627 LN 7627 PONDEROSA LN 8941 KITTIWAKE ST LITTLETON CO 80126 MICHAEL R LEVY & JULIE S LEVY 2233-140-03-005 R0102672 Residential TRACT 66 HOMESTEAD HILLS 1 7.15 AM/L 135-281$ 785,838 $ 62,560 7.15 HOMESTEAD PARKER 801388813 7686 RD 7686 HOMESTEAD RD 12167 S TALLKID CT PARKER CO 801388813 GRETCHEN M HALKER & MATTHEW T HALKER 2233-140-02-006 R0097316 Residential TRACT 33 EXC N 44 FT HOMESTEAD HILLS 1 7.62 AM/L$ 382,314 $ 30,440 7.62 HOMESTEAD PARKER 801380000 7691 RD 7691 HOMESTEAD RD 7691 HOMESTEAD RD PARKER CO 801380000 DALE W BASTIAN & MARYBETH E BASTIAN 2233-144-99-001 R0446310 Exempt ROW PINE VALLEY SUB $ - $ - 0 None 801042425 None None 100 3RD ST CASTLE ROCK CO 801042425 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS 2233-140-01-008 R0332979 Residential LOT 3 HOMESTEAD HILLS 1 AMENDED 6.51 AM/L$ 509,377 $ 40,550 6.51 HOMESTEAD PARKER 801380000 7565 RD 7565 HOMESTEAD RD 7565 HOMESTEAD RD PARKER CO 801380000 MICHELLE SAWYER & STEVEN SAWYER 2233-140-03-011 R0105451 Residential LOT 5 PINE VALLEY 2.98 AM/L$ 371,205 $ 29,540 2.98 ROBIN PARKER 801380000 7849 RD 7849 ROBIN RD 7849 E ROBIN RD PARKER CO 801380000 DEWIGHT BATT & COLLEEN BATT 2233-140-03-017 R0403970 Residential TRACT 65A HOMESTEAD HILLS 1 AS MODIFIED BY LOT LINE ADJ CERTS 9713092$ 455,690 $ 36,280 4.924 HOMESTEAD PARKER 801380000 7780 RD 7780 HOMESTEAD RD 7780 HOMESTEAD RD PARKER CO 801380000 ROBERT A HAEFLEIN & MARSHA K HAEFLEIN 2233-140-02-004 R0097076 Residential LOT 32 A PEARSON'S SUB 4.691 AM/L 332-115$ 831,139 $ 66,160 4.691 PONDEROSA PARKER 801380000 7742 LN 7742 PONDEROSA LN 7742 PONDEROSA LN PARKER CO 801380000 ALEKSEI M KAC ESTHER J KAC 2233-140-03-008 R0102541 Residential LOT 2 PINE VALLEY 2.44 AM/L$ 394,000 $ 31,360 2.44 ROBIN PARKER 801380000 7677 RD 7677 ROBIN RD 7677 E ROBIN RD PARKER CO 801380000 RYAN FAMILY TRUST 2233-140-02-007 R0091539 Residential TRACT 34 HOMESTEAD HILLS 1 TOTAL ACREAGE 5 AM/L$ 640,015 $ 50,950 5 HOMESTEAD PARKER 80138 7781 RD 7781 HOMESTEAD RD 7781 HOMESTEAD RD PARKER CO 80138 JON C BOESEN & KELLY M BOESEN 2233-140-03-016 R0403955 Residential TRACT 64A HOMESTEAD HILLS 1 AS MODIFIED BY LOT LINE ADJ CERTS 9713092$ 547,617 $ 43,600 4.912 HOMESTEAD PARKER 801380000 7842 RD 7842 HOMESTEAD RD 7842 HOMESTEAD RD PARKER CO 801380000 CHERYL A URBAN 2233-140-02-005 R0101266 Residential LOT 32 B PEARSON'S SUB 4.502 AM/L$ 521,089 $ 41,480 4.502 PONDEROSA PARKER 801380000 7676 LN 7676 PONDEROSA LN 7676 PONDEROSA LN PARKER CO 801380000 PAUL J VALDEZ & MONICA L JESCH 2233-140-03-010 R0101995 Residential LOT 4 PINE VALLEY 3.22 AM/L$ 434,067 $ 34,550 3.22 ROBIN PARKER 801380000 7813 RD 7813 ROBIN RD 7813 E ROBIN RD PARKER CO 801380000 MARY COLEMAN SEELY Total 67$ 48,517,591 $ 4,088,120 304.37 September 2019 PARCEL VALUES NO DAM 19117764

NO DAM SPN ACCOUNT # OWNER NAME LEGAL_DESC UPDATE DATE ACCOUNT TYPE ACTUAL VALUE ASSESSED VALUE 1 223310399008 R0338942 CDOT TR IN SW1/4 10‐6‐66. 0.1394 AM/L 5/24/2011 Exempt $0 $0 1 223310309012 R0209824 TOWN OF PARKER TRACT A PINE LANE 9.02 AM/L 7/30/2015 Exempt $54,120 $15,690 1 223310399007 R0304303 CDOT TRACT IN SW1/4 10‐6‐66 .861 AM/L 6/17/2009 Exempt $0 $0 1 223310399011 R0339815 CDOT 25 FT STRIP ALONG EAST R.O.W. HWY # 83 IN NW1/4SW1/4 10‐ 5/24/2011 Exempt $0 $0 1 223314001010 R0409753 SOLID ROCK TRUST LOT 18 CENTENNIAL RANCH 5.050 AM/L 10/26/2015 Residential $2,539,802 $202,170 1 223314001011 R0409754 RICHARD JENNINGS & LESLEY JENNINGS LOT 19 CENTENNIAL RANCH 2.740 AM/L 10/26/2015 Residential $1,965,592 $156,460 1 223315111005 R0459673 PARKER WATER & SANITATION DISTRICT LOT 2 LINCOLN CREEK VILLAGE FLG 1 1.37 AM/L 10/8/2015 Exempt $8,220 $2,390 1 223314001020 R0409762 BEVERLY J CRAVEN & E RANDY CRAVEN LOT 26 CENTENNIAL RANCH 3.830 AM/L 7/9/2004 Residential $1,068,624 $85,060 1 223315112003 R0459678 CONNIE D GERDES & PATTY A GERDES LOT 5 LINCOLN CREEK VILLAGE FLG 1 7.09 AM/L 2/4/2016 Vacant Land $617,681 $179,130 1 223315111003* MOST OF LOT 1 LINCOLN CREEK VILLAGE FLG 1 4.5 AM/L MTD 2/26/2014 *now broken up into smaller parcels for development 1 223314208006 R0451895 GRACE BAPTIST CHURH OF PARKER INC MOST PARCEL B STROH EXEMPTION PLAT 17.789 AM/L 2/1/2016 Exempt $225,000 $65,250 1 223314299015 R0482297 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS PART PARCEL B STROH EXEMPTION 0.732 AM/L PT PINE DR RO 2/1/2016 Exempt $878 $250 1 223314208005 R0451897 ALEJANDRO J KOFFMANN & JAMIE MARIE KOFFMANN PART PARCEL B STROH EXEMPTION PLAT 4.311 AM/L 2/1/2016 Residential $832,269 $66,250 1 223314299017 R0482299 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS PART PARCEL B STROH EXEMPTION 1.638 AM/L 2/4/2016 Exempt $1,966 $570 1 223314299013 R0482292 TOWN OF PARKER PART PARCEL B STROH EXEMPTION (PT PINE DR ROW) 0.256 A 2/4/2016 Exempt $307 $90 1 223310406026 R0446077 TOWN OF PARKER PT LOT 15 PARKER VILLAGE 1 0.790 AM/L 7/31/2012 Exempt $0 $0 1 223310399001 R0378293 TOWN OF PARKER PUBLIC STREETS LYING WITHIN THE BOUNDARIES OF MACLACHL 7/30/2015 Exempt $0 $0 1 223310399005 R0447141 CDOT ROW FOR HIGHWAY 83 (PARKER RD) IN SW1/4 10‐6‐66 8.50 A 6/5/2014 Exempt $0 $0 1 223310399032 R0485878 CDOT ROW FOR HWY 83 IN SW1/4 10‐6‐66 1.983 AM/L 6/9/2014 Exempt $0 $0 1 223315199023 R0482295 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS ROW IN NE1/4 & SE1/4 15‐6‐66 3.795 AM/L (PT PINE DR) 2/26/2014 Exempt $4,554 $1,320 1 223315199019 R0474734 TOWN OF PARKER ROW TRACT NE1/4NE1/4 15‐6‐66 4.033 AM/L AKA LINCOLN B 2/4/2016 Exempt $23,406 $6,790 1 223315199011 R0459688 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS ROW WITHIN LINCOLN CREEK VILLAGE FLG 1 2ND AMEND 0.63 10/8/2015 Exempt $0 $0 1 223314299010 R0409717 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS STREETS IN CENTENNIAL RANCH AKA PINE DR CENTENNIAL DR; J 1/14/2015 Exempt $0 $0 1 223310399004 R0446129 TOWN OF PARKER TR IN SW1/4 10‐6‐66 EASTSIDE OF STATE HWY 83 AKA PART OF P 7/31/2012 Exempt $0 $0 1 223315199020 R0474735 TOWN OF PARKER TR NE1/4NE1/4 15‐6‐66 1.000 AM/L MTD XXXXX 2/4/2016 Exempt $4,674 $1,360 1 223315100026 R0474736 TOWN OF PARKER TR NE1/4NE1/4 15‐6‐66 2.22 AM/L 10/8/2015 Exempt $13,320 $3,860 1 223314001009 R0409722 PARKER WATER & SANITATION DISTRICT TRACT A CENTENNIAL RANCH 4.780 AM/L 7/30/2012 Exempt $28,680 $8,320 1 223315111001 R0459669 LIBERTY SAVINGS BANK FSB TRACT A LINCOLN CREEK VILLAGE FLG 1 1.0 AM/L 2/26/2014 Vacant Land $6,000 $1,740 1 223310308001 R0382966 DIAMOND SHAMROCK STATIONS INC TRACT A MACLACHLAN SUB #1 0.50 AM/L 7/30/2015 Vacant Land $3,000 $870 1 223310310011 R0459414 TOWN OF PARKER TRACT A PARKER AUTO PLAZA FLG 1 8.10 AM/L 7/30/2015 Exempt $9,720 $2,820 1 223314001021 R0409723 CENTENNIAL RANCH HOMEOWNERS ASSOCIATION TRACT B CENTENNIAL RANCH 35.080 AM/L 8/7/2014 HOA $0 $0 1 223315111002 R0459670 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS TRACT B LINCOLN CREEK VILLAGE FLG 1 0.76 AM/L 10/8/2015 Exempt $4,560 $1,320 1 223310310007 R0396421 APEX CAPITAL INVESTMENTS INC TRACT B MACLACHLAN SUBDIVISION FILING #2. 1776 SQ FT OR 0 7/30/2015 Vacant Land $246 $70 1 223315112008 R0459683 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS TRACT C LINCOLN CREEK VILLAGE FLG 1 3.54 AM/L 10/8/2015 Exempt $21,240 $6,160 1 223310310013 R0459416 PARKER AUTO PLAZA OWNERS ASSOCIATION INC TRACT C PARKER AUTO PLAZA FLG 1 1.47 AM/L 7/17/2008 Commercial $8,820 $2,560 1 223315112009 R0459684 CONNIE D GERDES & PATTY A GERDES TRACT D LINCOLN CREEK VILLAGE FLG 1 0.69 AM/L 2/26/2014 Vacant Land $828 $240 1 223315112007 R0459682 CONNIE D GERDES & PATTY A GERDES TRACT E LINCOLN CREEK VILLAGE FLG 1 2.01 AM/L 4/3/2015 Vacant Land $2,412 $700 1 223310300030 R0362921 PUBLIC SERVICE CREDIT UNION TRACT IN SW1/4 10‐6‐66 1.061 AM/L 7/31/2012 Commercial $325,000 $94,250 Total $7,770,919 $905,690 $6,731,287 $604,190 September 2019 PARCEL VALUES DAM 19117764

DAM NO DAM SPN ACCOUNT # OWNER NAME LEGAL_DESC UPDATE DATE ACCOUNT TYPE ACTUAL VALUE ASSESSED VALUE 1 1 223310309012 R0209824 TOWN OF PARKER TRACT A PINE LANE 9.02 AM/L 7/30/2015 Exempt $54,120 $15,690 1 1 223314208006 R0451895 GRACE BAPTIST CHURH OF PARKER INC MOST PARCEL B STROH EXEMPTION PLAT 17.789 AM/L 2/1/2016 Exempt $225,000 $65,250 1 1 223314299017 R0482299 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS PART PARCEL B STROH EXEMPTION 1.638 AM/L 2/4/2016 Exempt $1,966 $570 1 1 223310406026 R0446077 TOWN OF PARKER PT LOT 15 PARKER VILLAGE 1 0.790 AM/L 7/31/2012 Exempt $0 $0 1 1 223310399001 R0378293 TOWN OF PARKER PUBLIC STREETS LYING WITHIN THE BOUNDARIES OF MACLACH 7/30/2015 Exempt $0 $0 1 1 223310399005 R0447141 CDOT ROW FOR HIGHWAY 83 (PARKER RD) IN SW1/4 10‐6‐66 8.50 A 6/5/2014 Exempt $0 $0 1 1 223315199023 R0482295 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS ROW IN NE1/4 & SE1/4 15‐6‐66 3.795 AM/L (PT PINE DR) 2/26/2014 Exempt $4,554 $1,320 1 1 223315199019 R0474734 TOWN OF PARKER ROW TRACT NE1/4NE1/4 15‐6‐66 4.033 AM/L AKA LINCOLN B 2/4/2016 Exempt $23,406 $6,790 1 1 223315199011 R0459688 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS ROW WITHIN LINCOLN CREEK VILLAGE FLG 1 2ND AMEND 0.6 10/8/2015 Exempt $0 $0 1 1 223314299010 R0409717 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS STREETS IN CENTENNIAL RANCH AKA PINE DR CENTENNIAL DR; 1/14/2015 Exempt $0 $0 1 1 223315199020 R0474735 TOWN OF PARKER TR NE1/4NE1/4 15‐6‐66 1.000 AM/L MTD XXXXX 2/4/2016 Exempt $4,674 $1,360 1 1 223314001009 R0409722 PARKER WATER & SANITATION DISTRICT TRACT A CENTENNIAL RANCH 4.780 AM/L 7/30/2012 Exempt $28,680 $8,320 1 1 223315111001 R0459669 LIBERTY SAVINGS BANK FSB TRACT A LINCOLN CREEK VILLAGE FLG 1 1.0 AM/L 2/26/2014 Vacant Land $6,000 $1,740 1 1 223310310011 R0459414 TOWN OF PARKER TRACT A PARKER AUTO PLAZA FLG 1 8.10 AM/L 7/30/2015 Exempt $9,720 $2,820 1 1 223314001021 R0409723 CENTENNIAL RANCH HOMEOWNERS ASSOCIATION TRACT B CENTENNIAL RANCH 35.080 AM/L 8/7/2014 HOA $0 $0 1 1 223315111002 R0459670 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS TRACT B LINCOLN CREEK VILLAGE FLG 1 0.76 AM/L 10/8/2015 Exempt $4,560 $1,320 1 1 223310310007 R0396421 APEX CAPITAL INVESTMENTS INC TRACT B MACLACHLAN SUBDIVISION FILING #2. 1776 SQ FT OR 7/30/2015 Vacant Land $246 $70 1 1 223315112008 R0459683 DOUGLAS COUNTY BOARD OF COUNTY COMMISSIONERS TRACT C LINCOLN CREEK VILLAGE FLG 1 3.54 AM/L 10/8/2015 Exempt $21,240 $6,160 1 1 223315112009 R0459684 CONNIE D GERDES & PATTY A GERDES TRACT D LINCOLN CREEK VILLAGE FLG 1 0.69 AM/L 2/26/2014 Vacant Land $828 $240 Total $384,994 $111,650 September 2019 Table 1 (MASTER) 19117764

TOTAL # OF GAP LAND USE TYPE (ACRES) TOTAL # OF TOTAL VALUE OF INUNDATION TOTAL BUILDINGS ON Cultivated Introduced Upland Introduced Upland Western Great Plains Western Great Plains Western Great INTERSECTED INTERSECTED Developed, High Developed, Low Western Great SCENARIO ACRES INTERSECTED Cropland/Open Vegetation ‐ Annual Vegetation ‐ Perennial Foothill and Piedmont Riparian Woodland and Plains Shortgrass PROPERTIES PROPERTIES Intensity Intensity Plains Floodplain PROPERTIES Space Grassland Grassland and Forbland Grassland Shrubland Prairie Dam 7.6 19 $384,994 2 3.71 0.29 0.02 0.00 2.37 0.00 0.51 0.52 0.22 No Dam 32.2 38 $7,770,919 7 16.38 2.15 0.05 0.68 7.90 0.23 1.64 2.66 0.76 Difference 25 19 $7,385,925 5 12.67 1.86 0.03 0.68 5.53 0.23 1.13 2.14 0.54

DATA SOURCES *Property information: Douglas County Assessor's Office. Up to date as of March 2017. *Land use/cover information: U.S. Geological Survey Gap Analysis Program‐ Land Cover Data v2.2 September 2019 Table 2 (100-year GIS Data) 19117764

Total Acreage Parcels/Structures Land Use Assessor's Values Infrastructure Total Total Acreage in Open Approx. No. Acreage in Floodplain No. of Space/Vacant Residential Commercial/In Approx. No. Approx. No. Approx. No. of Floodplain < 2 feet No. of Structures Lands in Lands in dustrial Lands Other Lands in Assessed of Roadway of Water of Sanitary Gas/Electric Depth > 2 Depth Parcels in in Floodplain Floodplain in Floodplain Floodplain Improved Value Structure Value Crossings Lines Sewer Lines Utilities Entity feet (acres) (acres) Floodplain Floodplain MH OS SL SLB TS TSB (acres) (acres) (acres) (acres) in Floodplain ($) ($) Impacted Impacted Impacted Impacted

With Dam 7.60.0192 001001 7.30.30.00.0 $ 384,994 $ - 0 0 0 0 Without Dam 7.624.6387 022012 30.32.20.00.07,$ 770,919 $ 905,690 4 2 1 2 Difference0.024.6195 021011 22.91.90.00.07,$ 385,925 $ 905,690 4 2 1 2 September 2019 Table 3 (Value Comps) 19117764

Estimated Value Type of Structure and Estimated Approximate Value Total Estimated Total Improved Land Total Structure Estimated Value in Value in Contents Entity Floodplain Floodplain Value MH OS SL SLB TS TSB

With Dam $ 384,994 $ - $ - $ - $ - $ - $ - $ - $ - Without Dam $ 7,770,919 $ 905,690 $ 393,975 $ - $ - $ - $ - $ - $ - Difference$ 7,385,925 $ 905,690 $ 393,975 $ - $ - $ - $ - $ - $ - September 2019 Table 4 (100-year Damage Calcs) 19117764

Estimated Structural and Estimated Estimated Emergency Traffic Clean-up & Contents Environmental Infrastructure Services Disruption Maintenance Entity Damages Damages1 Damages2 Costs3 Costs4 Costs5 TOTAL 500-year Event $418,139 $39,794 $376,183 $33,451 $724,632 $20,907 $1,613,106 100-year Event $361,248 $34,380 $325,000 $28,900 $626,040 $18,062 $1,393,630 50-year Event $156,397 $14,884 $140,704 $12,512 $271,034 $7,820 $603,350 10-year Event $15,791 $1,503 $14,207 $1,263 $27,366 $790 $60,919 5-year Event $0 $0 $0 $0 $0 $0 $0 2-year Event $0 $0 $0 $0 $0 $0 $0 Average Annual Damages $13,383 $1,274 $12,040 $1,071 $23,192 $669 $51,629

Infrastructure Peak Peak and Traffic Discharge Discharge Other Related Upstream of Downstream Damage Reductions Damages6 Damages6 Dam (cfs)7 of Dam (cfs)7 500-year 116% 116% 2560 627 100-year 100% 100% 1670 416 50-year 43% 43% 1350 352 10-year 4% 4% 700 223 5-year 0% 0% 89 15 2-year 0% 0% 58 11

Annual Inflation Rate 2.875% Project Life 100 years Present Worth Conversion Factor 32.74 Average Annual Damages $51,629 Present Worth Damages $1,690,273

Interval Probability Interval Average Annual Recurrence Interval Flood Probability Interval Damages ($) Damages ($) Damages ($) Damages ($) 2‐year 0.5 $ ‐ 0.3 $ ‐ $ ‐ $ ‐ 5‐year 0.2 $ ‐ 0.1$ 30,460 $ 3,046 $ 3,046 10‐year 0.1$ 60,919 0.08$ 332,135 $ 26,571 $ 29,617 50‐year 0.02$ 603,350 0.01$ 998,490 $ 9,985 $ 39,602 100‐year 0.01$ 1,393,630 0.008$ 1,503,368 $ 12,027 $ 51,629 500‐year 0.002$ 1,613,106

Vehicle Hours of Travel per Road Closures 42,300 hours Value of Travel ‐ Time Savings $ 14.80 per hour

Notes: 1. Environmental damages estimated at $1,500/acre for additional area impacted. 2. Infrastructure damages estimated as $25,000 per utility crossing impacted and $50,000 per roadway crossing impacted. 3. Emergency services costs estimated as 8% of structural and contents damages. 4. Traffic disruption costs based on traffic study prepared by Douglas County (Dec, 2018) and USDOT Benefit-Cost Analysis Guidance for Discretionary Grant Programs (June, 2018) 5. Clean-up and maintenance costs estimated as 5% of structural and contents damages. 6. Ratios of damages to 100-year flood event based on approximate ratios of FEMA floodplain discharges upstream and below of the dam compared to road/bridge capacity (500-year event with dam). 7. Peak discharges estimated from hydrologic data from FEMA and UDFCD. September 2019 B_C Summary Sheet 19117764

Parameter Total land removed from floodplain (acres) 1 24.6 Structures removed from floodplain 1 5 Parcels removed from floodplain 1 19 Open Space/Vacant land removed from floodplain (acres) 1 22.9 Roadways removed from flooding 1 4

Average Annual Damages Local Benefits Reduction in local damages (structures and contents)$ 13,383 Total Local Benefits$ 13,383 Regional Benefits Decreased access/traffic costs$ 23,192 Decreased clean-up costs$ 669 Decreased infrastructure losses$ 12,040 Decreased emergency services costs$ 1,071 Decreased water quality/environmental damages$ 1,274 Total Regional Benefits$ 38,246 Net Total Benefits$ 51,629 Present Worth Damages$ 1,690,273

Notes: 1. Based on estimated 100-year flooding extents. September 2019 Business_Road Data 19117764

Estimated Business/Critical Facility Monthly Income Building Type Grace Baptist Church 18811 Ponderosa Drive 18761 Ponderosa Drive

Estimated Daily Approx. 100-year Approx. 500-year Traffic Count Overtopping Overtopping Roadways (vehicles/day) Depth Depth Twenty Mile Road 2500 Parker Road 48000 0.5 1.0 Lincoln Avenue 13000 0.5 Village Creek Parkway 2500 Pine Drive 2500 1.0 1.5 Centennial Drive 200 3.0 4.0

Utilities (water, sewer, electric) Parker Water and Sanitation District September 2019 Table 5 (FIA Depth-Damage Info) 19117764

Federal Insurance Administration Depth Damage Curves

OS OS OS STRUCTURE CONTENTS Structure Contents DEPTH DAMAGE RELATIONSHIP DEPTH DAMAGE RELATIONSHIP DRY 0 DRY 0.00 0 0.17 0 0.12 avg 1-3' 0.23 0.31 1 0.17 1 0.24 2 0.25 2 0.33 3 0.28 3 0.35 4 0.3 4 0.37 5 0.31 5 0.41 6 0.4 6 0.45 7 0.43 7 0.50 8 0.43 8 0.55 9 0.45 9 0.60 10 0.46 10 0.60

MH MH MH STRUCTURE CONTENTS Structure Contents DEPTH DAMAGE RELATIONSHIP DEPTH DAMAGE RELATIONSHIP DRY 0 DRY 0.00 0 0.1 0 0.03 avg 1-3' 0.60 0.47 1 0.44 1 0.27 2 0.63 2 0.49 3 0.73 3 0.64 4 0.78 4 0.70 5 0.79 5 0.76 6 0.81 6 0.78 7 0.82 7 0.79 8 0.82 8 0.81 9 0.82 9 0.83 10 0.82 10 0.83

Descriptions

SL Single-level Residential SLB Single-level Residential with basement TS Two-story Residential TSB Two-story Residential with basement OS Commercial Structure MH Mobile Home September 2019 Table 6 (USACOE Depth-Damage) 19117764

Single Level no Basement (SL) Single Level with Basement (SLB) Two Story no Basement (TS) Two Story with Basement (TSB) Split Level no Basement Split Level with Basement Standard Standard Standard Standard Standard Standard Mean of Depth Structure Contents Deviation of Structure Contents Deviation of Structure Contents Deviation of Structure Contents Deviation of Structure Contents Deviation of Contents Deviation of Damage Damage Damage Damage Damage Damage Damage ‐8 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% ‐7 0.0% 0.0% 0.0% 0.7% 0.8% 1.3% 0.0% 0.0% 0.0% 1.7% 1.0% 2.1% 0.0% 0.0% 0.0% 0.0% 0.7% 0.0% ‐6 0.0% 0.0% 0.0% 0.8% 2.1% 1.1% 0.0% 0.0% 0.0% 1.9% 2.3% 2.1% 0.0% 0.0% 0.0% 2.5% 1.4% 1.8% ‐5 0.0% 0.0% 0.0% 2.4% 3.7% 0.9% 0.0% 0.0% 0.0% 2.9% 3.7% 1.8% 0.0% 0.0% 0.0% 3.1% 2.4% 1.6% ‐4 0.0% 0.0% 0.0% 5.2% 5.7% 0.9% 0.0% 0.0% 0.0% 4.7% 5.2% 1.7% 0.0% 0.0% 0.0% 4.7% 3.8% 1.5% ‐3 0.0% 0.0% 0.0% 9.0% 8.0% 0.9% 0.0% 0.0% 0.0% 7.2% 6.8% 1.6% 0.0% 0.0% 0.0% 7.2% 5.4% 1.6% ‐2 0.0% 0.0% 0.0% 13.8% 10.5% 0.9% 0.0% 0.0% 0.0% 10.2% 8.4% 1.5% 0.0% 0.0% 0.0% 10.4% 7.3% 1.6% ‐1 2.5% 2.4% 2.7% 19.4% 13.2% 0.8% 3.0% 1.0% 4.1% 13.9% 10.1% 1.4% 6.4% 2.2% 2.9% 14.2% 9.4% 1.6% 0 13.4% 8.1% 2.0% 25.5% 16.0% 0.9% 9.3% 5.0% 3.4% 17.9% 11.9% 1.3% 7.2% 2.9% 2.1% 18.5% 11.6% 1.6% 1 23.3% 13.3% 1.6% 32.0% 18.9% 1.0% 15.2% 8.7% 3.0% 22.3% 13.8% 1.4% 9.4% 4.7% 1.9% 23.2% 13.8% 1.7% 2 32.1% 17.9% 1.6% 38.7% 21.8% 1.1% 20.9% 12.2% 2.8% 27.0% 15.7% 1.5% 12.9% 7.5% 1.9% 28.2% 16.1% 1.9% 3 40.1% 22.0% 1.8% 45.5% 24.7% 1.4% 26.3% 15.5% 2.9% 31.9% 17.7% 1.8% 17.4% 11.1% 2.0% 33.4% 18.2% 2.1% 4 47.1% 25.7% 1.9% 52.2% 27.4% 1.6% 31.4% 18.5% 3.2% 36.9% 19.8% 2.0% 22.8% 15.3% 2.2% 38.6% 20.2% 2.4% 5 53.2% 28.8% 2.0% 58.6% 30.0% 1.9% 36.2% 21.3% 3.4% 41.9% 22.0% 2.3% 28.9% 20.1% 2.4% 43.8% 22.1% 2.6% 6 58.6% 31.5% 2.1% 64.5% 32.4% 2.1% 40.7% 23.9% 3.7% 46.9% 24.3% 2.6% 35.5% 25.2% 2.7% 48.8% 23.6% 2.9% 7 63.2% 33.8% 2.2% 69.8% 34.5% 2.4% 44.9% 26.3% 3.9% 51.8% 26.7% 2.9% 42.3% 30.5% 3.2% 53.5% 24.9% 3.2% 8 67.2% 35.7% 2.3% 74.2% 36.3% 2.5% 48.8% 28.4% 4.0% 56.4% 29.1% 3.1% 49.2% 35.7% 3.8% 57.8% 25.8% 3.4% 9 70.5% 37.2% 2.4% 77.7% 37.7% 2.7% 52.4% 30.3% 4.1% 60.8% 31.7% 3.4% 56.1% 40.9% 4.5% 61.6% 26.3% 3.6% 10 73.2% 38.4% 2.7% 80.1% 38.6% 2.8% 55.7% 32.0% 4.2% 64.8% 34.4% 3.7% 62.6% 45.8% 5.3% 64.8% 26.3% 3.9% 11 75.4% 39.2% 3.0% 81.1% 39.1% 2.9% 58.7% 33.4% 4.2% 68.4% 37.2% 4.2% 68.6% 50.2% 6.0% 67.2% 26.3% 4.2% 12 77.2% 39.7% 3.3% 81.1% 39.1% 2.9% 61.4% 34.7% 4.2% 71.4% 40.0% 5.0% 73.9% 54.1% 6.7% 68.8% 26.3% 4.8% 13 78.5% 40.0% 3.7% 81.1% 39.1% 2.9% 63.8% 35.6% 4.2% 73.7% 43.0% 6.2% 78.4% 57.2% 7.4% 69.3% 26.3% 5.7% 14 79.5% 40.0% 4.1% 81.1% 39.1% 2.9% 65.9% 36.4% 4.3% 75.4% 46.1% 7.8% 81.7% 59.4% 7.9% 69.3% 26.3% 5.7% 15 80.2% 40.0% 4.5% 81.1% 39.1% 2.9% 67.7% 36.9% 4.6% 76.4% 49.3% 9.8% 83.8% 60.5% 8.3% 69.3% 26.3% 5.7% 16 80.7% 40.0% 4.9% 81.1% 39.1% 2.9% 69.2% 37.2% 5.0% 76.4% 52.6% 12.4% 84.4% 60.5% 8.7% 69.3% 26.3% 5.7% September 2019 Table 7 (Unit Rates) 19117764

Benefits Data Average Value Min Value Max Value Unit Floodplain Easement $18,500 $10,000 $24,000 acre Estimated Contents Value1 43.5% 10% 250% percent of structure value Single Story‐No Basement 43.4% 10% 250% percent of structure value Single Story‐Basement 43.5% 10% 246% percent of structure value Two Story‐No Basement 40.2% 10% 249% percent of structure value Two Story‐Basement 44.1% 10% 250% percent of structure value Split Level‐No Basement 42.1% 10% 249% percent of structure value Split Level‐Basement 43.5% 10% 246% percent of structure value Mobile Home 63.6% 10% 247% percent of structure value Increased Land Value $15,000 $5,000 $40,000 acre 1. Values adopted from EM 1110‐2‐1619, Risk Based Analysis for Flood Damage Reduction Studies (USACOE, 1996) 2. Adopted from Economic Guidance Memorandum (EGM) 04‐01, Generic Depth‐Damage Relationships for Residential Structure s (USACOE, 2003) 3. From Federal Insurance Administration Depth‐Damage Curves.

Consequences Data Average Value Min Value Max Value Unit Percent Structure Damages Single-level Residential (SL)2 32.1% 13.4% 41.9% percent Single-level Residential with basement (SLB)2 38.7% 25.5% 46.9% percent Two-story Residential (TS)2 20.9% 9.3% 29.2% percent Two-story Residential with basement (TSB)2 27.0% 17.9% 33.7% percent Commercial Structure (OS)3 23.3% 17.0% 28.0% percent Mobile home (MH)3 60.0% 10.0% 73.0% percent Percent Contents Damages Single-level Residential (SL)2 17.9% 8.1% 23.8% percent Single-level Residential with basement (SLB)2 21.8% 16.0% 26.1% percent Two-story Residential (TS)2 20.9% 5.0% 18.4% percent Two-story Residential with basement (TSB)2 15.7% 11.9% 19.5% percent Commercial Structure (OS)3 30.7% 12.0% 41.0% percent Mobile home (MH)3 46.7% 3.0% 76.0% percent Percent Emergency Services Costs 8.0% 3.0% 15.0% percent Percent Clean-up/Maintenance Costs 5.0% 2.0% 8.0% percent Estimated Infrastructure Damages $25,000 $3,000 $100,000 per crossing Agricultural Losses $500 $200 $2,000 acre Environmental Damages $1,500 $700 $2,500 acre Roadway Damages $50,000 $25,000 $200,000 per crossing

Construction Unit Costs Average Value Min Value Max Value Unit Embankment $7 $6 $10 cubic yard Excavation $3 $2 $6 cubic yard Excavate & Haul $7 $5 $10 cubic yard In-channel Work (cut and fill) $10 $6 $16 cubic yard Concrete (CIP-Reinforced) $700 $500 $1,000 cubic yard Concrete (Non-reinforced) $300 $250 $500 cubic yard CIP Headwalls $400 $200 $800 linear feet CIP Wingwalls $1,080 $700 $1,600 each Riprap (12-24" diameter) $80 $60 $110 cubic yard Asphalt Roads $7 $6 $10 sq. feet Gravel Roads $7 $6 $10 cubic yard Road Reconstruction $7 $6 $10 sq. feet Railroad Reconstruction $500 $250 $700 linear foot Fence $4 $3 $5 linear foot Revegetation/seeding $7,000 $5,000 $10,000 acre Topsoil (remove and replace) $5 $4 $6 cubic yard Reservoir Storage (purchase) $2,000 $800 $15,000 acre-foot Irrigation siphon crossing $100,000 $60,000 $150,000 each

Other Costs Average Value Min Value Max Value Unit Construction Contingency 30% 25% 40% percent Engineering/Permitting 15% 10% 20% percent Engineering Costs to Manage FP $30,000 $10,000 $40,000 per parcel Legal Fees 3% 2% 5% percent Unlisted Items 10% 5% 15% percent City Management Expenses 5% 3% 6% percent Floodproofing $75,000 $35,000 $100,000 per structure

FEMA Approved BCA Rates (adjusted) Average Value Min Value Max Value Unit Monthly Rental Costs $1.50 $0.75 $2.00 per sf/month Disruption Costs $22.00 $21.00 $24.00 per hour Vehicle Displacement Costs $32.00 $30.00 $34.00 per vehicle/hour Electric Power Outage $190.00 $180.00 $195.00 per capita/day Water-Potable $410.00 $390.00 $450.00 per capita/day Water-Irrigation $45.00 $35.00 $50.00 per capita/day Wastewater $35.00 $32.00 $40.00 per capita/day September 2019 Alts. Matrix 19117764

Scoring Criteria * Operation and Implementation Feasibility of Public Construction Feasibility of Maintenance Total Costs Implementation Safety Risk Funding Issues Addtl. Roadway Alternative ID Rank Conveyance Addtl. Estimated Alternative 15% 20% 25% 20% 10% 10% 100% Approx. Initial Improvement Legal/Floodplain Annual O&M Benefit/Cost No. Capital Cost Costs Management Fees Cost Ratio B/C Rank * Scoring from 1 to 5 where 1 is the best option 1 No Action (Future Without Project) 4.0 5.0 5.0 2.0 4.0 1.0 3.8 7 $ 27,200,000 $ 250,000 $ 2,500 0.1 6 2 Decommissioning 4.0 4.5 5.0 2.0 4.0 1.0 3.7 6 $ 27,800,000 $ - $ 250,000 $ 2,500 0.1 7 3 Existing Spillway Modifications (Significant Hazard) 5.0 4.0 3.0 3.5 2.0 2.0 3.4 4 $ 25,700,000 $ - $ - $ 7,500 0.1 5 4 RCC Overtopping Protection 5.0 4.0 3.0 3.0 4.0 3.0 3.6 5 $ 7,000,000 $ - $ - $ 7,500 0.2 3 5 RCC (High Hazard) Spillway 2.0 2.0 1.0 1.0 2.0 2.0 1.6 1 $ 2,800,000 $ - $ - $ 5,000 0.6 1 6 RCC (Significant Hazard) Spillway and Floodproofing 5.0 4.0 3.0 1.0 4.0 2.5 3.2 3 $ 24,600,000 $ - $ - $ 7,500 0.1 4 7 New Principal and RCC Auxiliary Spillway 3.0 3.0 2.0 2.0 2.0 1.5 2.3 2 $ 2,900,000 $ - $ - $ 5,000 0.6 2

ATTACHMENT D-3 Computation of Population at Risk (PAR)

COMPUTATION OF POPULATION AT RISK (PAR)

STATE CO BY MWB DATE 6/15/17

DAM Franktown-Parker Watershed Dam FP-B1 CHECKED BY SWR DATE 6/15/17

DESIGN HAZARD YEAR BUILT 1964 L DRAINAGE AREA 2.27 mi2 CLASS CURRENT HAZARD WORK PLAN DATE 1971 H DAM HEIGHT 27 ft CLASS ver sht 1 of 1 POPULATION AT RISK DURING DAM FAILURE 2013-01 Number of Structures PAR per Exposure Structures (Elevated) Impacted by Inundation Depth Above Natural with Inundation PAR Potential Breach Ground Total Depths >=2.0 Ft. <2.0 Ft >=2.0 Ft.

Mobile Homes 0 02.6 0

Seasonal Use RV's 0 0

Other 00

Number of Structures PAR per Exposure Structures (With Foundations) Impacted Inundation Depth Above Natural with Inundation PAR by Potential Breach Ground Total Depths >=1.0 Ft. <1.0 Ft >=1.0 Ft.

Homes 1 12.6 3

Seasonal Use Homes and Cabins 0 0

Duplexes 0 0

Apartments 010 0

Commercial Buildings 05 0

Schools (Not in Use) 05 0

Hospitals (in Use) 020 0

Other (motels) 030 0 213 units

Number of Roads, Highways and Railways PAR per Exposure Highways and Railroads Road Overflow Depth with Inundation PAR Total Depths >=1.0 Ft. <1.0 Ft >=1.0 Ft. Main Local Roads and Minor State Highways Centennial Drive, Villagecreek Parkway 2 22 4

Pine Drive 1 12 2

Major State and Minor Federal Highways

SH 83 (Parker Road) 1 14 4

Highway Name(s) or Number(s) 04 0

Major Federal and Interstate Highways

I-25 008

Highway Name(s) or Number(s) 08 0

Railroads

UPSF Freight Traffic Only 03 0

Amtrak Passenger Traffic 020 0 TOTAL NUMBER OF PEOPLE AT RISK (PAR) 13

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