Author: frstormflood

AARON T. CVAR, Ph.D., P.E.

PROFESSIONAL REGISTRATION
Colorado Professional Engineer 
Wyoming Professional Engineer

EDUCATION
B.S., Civil Engineering, Colorado State University, 1996
M.S., Civil Engineering, Colorado State University, 1999 
Ph.D., Civil Engineering, Colorado State University, 2014

President/Owner (2008-present) – Front Range Stormwater & Floodplain Consulting, LLC, Fort Collins, Colorado.  > Provided expert testimony and forensic engineering studies in support of water-related litigation  > Conducted flood studies, and provided consultation regarding FEMA flood map interpretation, Letters of Map Revision (LOMR)  > Provided consulting involving storm water management plans (SWMP) and storm drainage plans, reports, and design > Designed irrigation systems, irrigation ponds, and flow measurement structures > Applied Geographic Information Systems to numerous hydrologic studies  Project Engineer (1999-2004), Senior Engineer (2004-2008) – Northern Engineering Services, Inc., Fort Collins, Colorado.  > Managed teams of engineers and production staff, provided mentoring and guidance > Successfully managed project budgets and schedules  > Provided expert testimony and forensic engineering studies in support of water-related litigation  > Conducted numerous master drainage studies and stormwater plans for residential, commercial, and municipal projects.  > Worked comprehensively with FEMA’s National Flood Insurance Program on interpretation of flood mapping and application of FEMA Regulations  > Prepared numerous floodplain analyses and studies according to FEMA guidelines > Managed land development projects-ensured quality design and drafting of grading plans, pipelines, and basic infrastructure  > Observed construction of pipelines, detention ponds, stormwater channels and provided post-construction certification  > Incorporated sustainability, Best Management Practices (BMPs), Low Impact Design (LID) into the design of numerous detention and water quality ponds, open channels, and general drainage designs Associate Water Resource Engineer (1998-1999) – Ballofet and Associates, Inc., Fort Collins, Colorado. > Assisted with Research and formulation of water supply master plan studies > Designed detention and water quality ponds, drainage channels, and storm sewer systems >Drafted construction drawings for drainage infrastructure Development Review Engineer (1997-1998) – City of Fort Collins Stormwater Utility, Fort Collins, Colorado. > Reviewed stormwater quality and erosion control plans, drainage plans, and drainage reports for compliance with City drainage criteria  > Approved post-construction drainage certifications for detention ponds, water quality ponds, open channels, and other drainage infrastructure  > Inspected construction sites to ensure proper best management practices and erosion control measures were in place and functional > Communicated verbally and in writing with design consultants and contractors on design issues, code and criteria violations Engineering Intern (summer 1996) – Northstar Engineering and Surveying, Inc., Pueblo, Colorado. > Designed detention ponds, small open channels and storm line systems > Drafted drafted plans in AutoCad for stormwater infrastructure and general construction details   > Worked portion of summer with survey crew and experienced general survey work with Total Station survey equipment SELECTED PROJECT EXPERIENCE STORMWATER ANALYSIS/DESIGN East I-25 Basin Drainage Master Plan, Loveland, Colorado – 1.5 square mile master drainage study South Gateway Master Drainage Study, Laramie, Wyoming – 300 ac. stormwater modeling study   Master Drainage Study for Highland Meadows Golf Course Subdivision, Windsor, Colorado – 640 ac. master drainage study  Master Drainage Study for Timnath Ranch Third Filing, Timnath, Colorado – 600 ac. master drainage study  Master Drainage Study for Timnath South Subdivision, Timnath, Colorado – 370 ac. master drainage study  Master Drainage Study for Wellington East, Wellington, Colorado – 300 ac. master drainage study  Storm Drainage Design for Timnath Ranch Third Filing, Timnath, Colorado – 600 ac. site drainage infrastructure design (commercial and residential mix) Storm Drainage Design for Timnath South Subdivision, Timnath, Colorado – 370 ac. site drainage infrastructure design (residential) Storm Drainage Design for Centerra East, Loveland, Colorado – 300 ac. site drainage infrastructure design (commercial) Storm Drainage Design for Windshire Park, Windsor, Colorado – 200 ac. site drainage infrastructure design (residential) Storm Water Management Plan (SWMP) – Centerra Parkway Expansion, Loveland, Colorado – Formulated SWMP for half-mile roadway expansion  Storm Water Management Plan (SWMP) – Centerra East Drainage Infrastructure, Loveland, Colorado – Formulated SWMP for construction of drainage infrastructure for 300 ac. commercial site Storm Water Management Plan (SWMP) – Hageman Earth Cycle, Fort Collins, Colorado – Formulated SWMP for commercial site handling recycling of yard waste and landscaping materials  Storm Water Management Plan (SWMP) – AFCO Steel Plant, Greeley, Colorado – Formulated SWMP for industrial site handling and storing steel products Storm Water Management Plan (SWMP) – Ranch-Way Feeds, Fort Collins, Colorado – Formulated SWMP for commercial site handling and storing agricultural feed products  FLOODPLAIN ANALYSIS/STUDIES Letter of Map Revision (LOMR) for Interchange Business Park, Fort Collins, Colorado – Half-mile FEMA jurisdictional floodplain map revision  Conditional Letter of Map Revision (CLOMR) for Block One Commercial Development, Fort Collins, Colorado – FEMA jurisdictional floodplain map revision including re-work of effective HEC-2 modeling of Cache La Poudre River Letter of Map Revision (LOMR) for The Town of Severance, Severance, Colorado – 1.5-mile FEMA jurisdictional floodplain map revision Letter of Map Amendment (LOMA) for Timnath Ranch Third Filing, Timnath, Colorado – One-mile FEMA jurisdictional floodplain map amendment  Letter of Map Revision (LOMR) for Lee MLD, Fort Collins, Colorado –Quarter-mile FEMA jurisdictional floodplain and floodway map revision Letter of Map Revision Based on Fill (LOMR-F) for Wellington Downs, Wellington, Colorado – 15 ac. multi-lot LOMR-F to remove lots from FEMA jurisdictional floodplain Letter of Map Revision Based on Fill (LOMR-F) for Poudre Heights, Windsor, Colorado – 10 ac. multi-lot LOMR-F to remove lots from FEMA jurisdictional floodplain Letter of Map Revision Based on Fill (LOMR-F) for Soth residence, Larimer County, Colorado – single lot LOMR-F and accompanying flood hydrology and hydraulic study to remove residence from FEMA jurisdictional floodplain Flood Study for Mountain Greenery Resort, Larimer County, Colorado – Quarter-mile flood hydrology and hydraulic study under Larimer County jurisdiction Approximate Zone A Flood Study for Androvich Property, Weld County, Colorado – Flood hydrology and hydraulic study under Weld County jurisdiction to establish 100-year peak discharge rate and Base Flood Elevations Approximate Zone A Flood Study for Hammond Property, Larimer County, Colorado – Flood hydrology and hydraulic study under Larimer County jurisdiction to establish 100-year peak discharge rate and Base Flood Elevations and floodway  Breach Analysis and Inundation Study for John Law Reservoir, Severance, Colorado – Modeled dam breach scenario for irrigation reservoir, and resulting flood wave inundation through multiple downstream proposed and existing residential subdivisions.  Breach Analysis and Inundation Study for Bayfield Water Treatment Plant, Bayfield, Colorado – Modeled dam breach scenario for water treatment plant reservoir, and resulting flood wave inundation through existing residential and commercial areas.  Relocation of McClellands Creek Channel, Fort Collins, Colorado – Quarter-mile floodplain channelization study and design under City of Fort Collins jurisdiction EXPERT WITNESS/LITIGATION SUPPORT Expert Testimony – Schiller Case, Logan County, Colorado – Provided expert testimony and forensic engineering study for litigation involving flooding of farm   Expert Testimony – Wall Case, Weld County, Colorado – Provided expert testimony and forensic engineering study for litigation involving flooding of residence   Forensic Engineering Study – Foothills Estates Subdivision, Larimer County, Colorado – Provided forensic engineering study for litigation involving subdivision flooding Forensic Engineering Study – Coyote Ranch Apartments, Denver, Colorado –Provided forensic engineering study for litigation involving apartment complex flooding Forensic Engineering Study – Ace Hardware of Wellington, Wellington, Colorado – Provided forensic engineering study for litigation involving flooding of business DRAINAGE MITIGATION STUDIES Drainage Mitigation Study – Stadium Village Apartments, Fort Collins, Colorado – Conducted mitigation study for appartment complex flooding Drainage Mitigation Study – Villas at Ptarmigan, Windsor, Colorado – Conducted mitigation study and designed solutions for subdivision drainage problemsDrainage Mitigation Design – Wall Residence, Weld County, Colorado- Provided design construction plans for pump system to mitigate flooding  Drainage Mitigation Design – Harmony Crossing Subdivision, Fort Collins, Colorado – Provided design construction plans for mitigation of failing detention pond outlet structure

Bioretention cells are also commonly referred to as  “Rain Gardens”.  Porous Landscape Detention (PLD) is also a type of bioretention.  Bioretention is typically utilized in more intensely developed areas  – commercial, multi-family developments, etc.  Often, bioretention cells are designed for confined spaces such as: 

• Parking lot islands
• Street medians
• Landscaped areas between drives, parking areas, roads and sidewalks, etc.
• Planter boxes collecting roof drains, street drains, etc.

The soil mixture/growing media is critical for a bioretention cell. See recommendations on soil mixtures in the Urban Storm Drainage Criteria Manual  (USDCM) Volume 3, by the Urban Drainage and Flood Control District, December 2010.

Urban Drainage and Flood Control District website 

It is critical that bioretention cells be protected during the construction process from sources of sediment.  In typical construction, large areas of land can be left exposed to erosion.  If a bioretention cell is downstream of areas of exposed/unvegetated land, there is potential for large volumes of sediment to be discharged into the cell during a storm event.  This could result irreparable damage to the growing media of the cell.

Photos: A. Cvar

Extended Detention is probably one of the most effective green stormwater practices, and is also one of the most practical means of achieving stormwater sustainability goals.

How Does Extended Detention Work? 

Stormwater can hold a number of pollutants:

• Solids
• Nutrients
• Pathogens
• Suspended Solids
• Trash 
• Metals
• Oils

Extended Detention allows for settling of suspended solids.  Many pollutants bind to suspended solids, and by removing these solids, we can enhance stormwater quality.

Smaller, more frequent storms are the predominant factor in stormwater pollutant loading.  The Extended Detention Basin’s holding volume is intended to capture runoff from the average storm event.  Typically, Extended Detention Basins are designed to capture runoff from the average storm (approximately a 1-year runoff event) and release over a 40-hour period. Again, this time period can vary with municipalities and drainage criteria.

Photos: A. Cvar

How does sustainability and green practices relate to stormwater?

When you think of true stormwater sustainability, you think of what happens in nature.  Nature has it’s own way of:

• Reducing runoff volumes by infiltration
• Reducing soil loss through vegetation
• Reducing pollutants in storm runoff by infiltration and biological uptake

What are we trying to achieve with stormwater sustainability?

Nature is a good example to follow as it works to reduce runoff volumes by infiltration, reduce soil loss through vegetation, enhance habitat,  and reduce pollutants in storm runoff by infiltration and biological uptake.

When we develop land, we change the natural system. Often, we increase both the peak runoff rate (typically measured in cubic feet per second, CFS) as well as the volume of runoff (typically measured in cubic feet or acre feet).  The increase in both developed runoff rate and volume can be harmful to downstream channels, resulting in degradation.  This degradation has effects on habitat as well as water quality by increasing sediment loads.

In addition to increasing runoff, we also introduce new sediment loads and pollutants into the natural system through the development process.  During construction, we can introduce new sediment loads by exposing previously vegetated soil.  After development is completed, we often see a whole new set of pollutants in storm runoff.

The primary objectives of stormwater sustainability are to mitigate these changes to the natural system.  
We can do this by:

1. Incorporating Construction BMP’s
2. Encouraging Stormwater Infiltration
3. Incorporating Stormwater Infiltration
4. Implementing Stormwater Settling Basins

1—Incorporate Contruction BMP’s

BMPs during construction should be implemented to reduce erosion, capture sediment, and contain hazardous materials. 

2–Encourage Stormwater Infiltration

Increases in both runoff rate and volume resulting from land development can be harmful to downstream systems.  By encouraging infiltration, we are seeking to mitigate the effects of land development.

Infiltration can also improve water quality through filtration and biological uptake which occur during the infiltration process.

3—Incorporate Stormwater Filtration

Developed runoff can contain a number of pollutants such as suspended solids, trash, and oils.  Filtration can be an effective means at removal of such pollutants.

4—Implement Stormwater Settling Basins

Many of the pollutants in stormwater bind to suspended solids/sediment.  By removing suspended solids, we can also reduce pollutants in stormwater.  Additionally, removing suspended solids helps downstream channels and receiving waters by reducing sediment loading.

A common design standard is to capture a certain amount of stormwater runoff (roughly the volume of a 1-year storm event) and release the water slowly over a 40-hour period.  This holding period allows for the settling of suspended solids in turbid stormwater.

Photos: A. Cvar

Sustainable practices such as extended detention, flat grading of pond bottom, micropools, and trickle channels can often be incorporated into the lower stage of detention ponds.

Extended Detention has been shown to have a very high total suspended solid (TSS) removal rate. Extended detention can often be incorporated into the lower stage of detention ponds, and is therefore very practical to implement.  Typically, Extended Detention volume is roughly 5% to 10% of required detention volume.  Adding an Extended Detention component to a detention pond is typically not a significant encumbrance.

One of the main challenges with integration of extended detention with detention is pond maintenance and outlet clogging.

An important question is, how will the pond be landscaped?  Do you expect a high volume of vegetation that can clog outlets?

Photos: A. Cvar

Depending on the municipality, detention ponds are required to hold different volumes of storm runoff. Often, detention ponds are required to hold up to a 100-year storm volume, and release at a 2-year or 10-year historic rate of flow.

 Such a pond would have a “2-stage” outlet structure.  For the first stage, the structure would release up to a certain flow rate at up to the 2-year storm volume.  For the second stage, the structure would release up to a certain flow rate at up to the 100-year storm volume.

Wet ponds can add tremendous aesthetic value to a project. When we talk about a “wet” pond, we are typically referring to a detention pond that functions also as a holding pond.  Stormwater can be detained on top of the permanent storage volume.  The storage volume may be there for practical reasons such as holding a certain amount of irrigation water, or simply for aesthetic purposes.

Some considerations with wet detention ponds:

Photos: A. Cvar

Detention Ponds are not typically designed to reduce the volume of storm runoff (typically measured in cubic feet or acre feet); rather, their intent is to reduce the runoff rate (typically measured in cubic feet per second, CFS).

In order to reduce the volume of storm runoff, it is necessary to implement design features which enhance infiltration.

Runoff is  stored in this underlying gravel layer and allowed to slowly infiltrate into the soil below. Seeing the installation steps for a porous paver system can be illustrative. 

The installation steps for a porous paver system are outlined below.

The black fabric seen in the picture is a geotextile filter fabric, intended to prevent the intermingling of the gravel and the underlying soil.

Photos: A. Cvar