14000000038 SOW

• Contract/PO #: 14000000038
• Contractor Name: Applied Weather Associates
• Contract Type: Grant
• Loan Projects - Doc Type: Contract Documents

• S
those from HMRs 51 and 55A. This study is following the same procedures used in the recently
completed Nebraska and Ohio statewide PMP studies. A grid has been delineated across the
entire domain. Each storm is then maximized in-place and transpositioned to appropriate grid
point(s) following standard procedures. For locations in the upper reaches of the watershed
where topography plays a significant role in rainfall production and distribution,the effects of
topography(orographic effects) are explicitly calculated using the Orographic Transposition
Factor methodology. All data and calculations will be performed using the PMP Evaluation
Tool to ensure reproducibility and expediency in use of the data and PMP derivation.
Recently Completed Projects
Arizona statewide PMP
This study provided updated PMP values for the entire state of Arizona. These values
have replaced those from HMR 49. This study followed the storm based approach which
analyzes the most extreme rainfall events over the entire period of record in all regions
considered transpositionable to any point within the state. Because HMR 49 is so outdated and
did not analyze storms using the current methodology followed in all other current HMRs, a
large number of storms required a full storm analysis. The 51 new storms analyzed as part of
this study provided an immense database of storm information for use in PMP development and
other hydrologic evaluations. Each storm was maximized in-place and transpositioned to
appropriate locations using a 2.5-square mile grid (over 64,000 grid points in total) covering all
of Arizona and surrounding regions. During the transposition process,the horizontal difference
in moisture were calculated and the effects of topography(orographic effects)were explicitly
calculated using the Orographic Transposition Factor methodology. In order to process and store
this large amount of data and large number of calculations,the PMP Evaluation Tool was
developed. Calculating the PMP values using the PMP Evaluation Tool provided for
reproducibility and expediency in use of the data and PMP derivation. Data and analysis from
this study are directly useable for work in this EPAT evaluation and any future PMP work in the
state of Colorado.
Lewis River site-specific PMP
This study provided updated PMP values for a large watershed in the southern Cascade
Mountains of Washington where topography played a major role in PMP development. These
values replaced those from HMR 57. This study followed the same procedures used in the
recently completed Arizona statewide PMP study. This was a storm based approach which
analyzes the most extreme rainfall events over the entire period of record in all regions
considered transpositionable to any point within the basin. Each storm was then maximized in-
place and transpositioned to a set of grid points covering the basin at a 2.5-square mile
resolution. During the transposition process,the horizontal difference in moisture were
calculated and the effects of topography(orographic effects)were explicitly quantified using the
Orographic Transposition Factor methodology. The PMP values for this basin were the result of
Atmospheric River storm events producing large amounts of rainfall on top of antecedent snow
pack from the fall through spring seasons. Appropriate meteorological time series data for use in
snow melt calculations were determined and applied for the PMP/PMF. Techniques and
understanding of mountainous topography on rainfall and PMP gained from this study are
directly useable for work in this EPAT review as well as future PMP work in the state of
Colorado.
Nebraska statewide PMP