A Brief Analysis of River
Flooding Along Major Basins in the Albany and Buffalo, NY WFO County Warning Areas
Department of Earth and Atmospheric Sciences
University at Albany, State University of New York
and National Weather Service, Buffalo, NY
A comprehensive and statistical
analysis was done for major river basins in the Albany
and Buffalo, NY
weather forecast office county warning areas to determine the distribution and
magnitude of river flooding. This was done on a monthly and seasonal
basis along with an examination of the causes of each of the flooding
events. Results from this research are an important advancement towards
increased operational awareness of distinct flooding patterns in both
regions. This study both identifies and ranks the months, seasons,
locations, and causes of floods in the Albany
and Buffalo county
warning area basins.
River flooding is a major forecast problem for many
National Weather Service Offices (NWS). There are several large basins
within the Albany and Buffalo NWS
county warning areas (CWA), which are prone to flooding. Forecasters in
these offices have river forecast models and other tools to aid them in making
river forecasts and warnings of river flooding. However, climatology of
river flooding specifically created for their CWA could prove to be another
valuable forecasting tool. This research was provided for the central NY
region (Binghamton office) by
Matthew Noyes (a student out of Cornell), and is viewed by the forecasters as a
very informative reference for river flooding. Thus, further research on
this subject was encouraged in other regions of NY. This study and the
previous are comprehensive and statistical analyses, aimed to identify the
months and locations of most frequent flooding along major NY state river
basins. A preliminary analysis of the causes of these floods is also
This study presents the results
of a statistical analysis of river crest data from dating back to the beginning
of the 20th century. These data used was obtained from for 17
gauges along the Albany CWA river basins and 17 gauges along the Buffalo CWA
river basins (Fig.1), (Table, 1). Frequency and magnitude of
flooding at several of these gauges may have been affected by flood control
efforts taken during the 20th century. Accounting for these
flood control efforts during this study was not possible (Noyes, 2000).
Table 1. Basins and Gauge Locations
Falls, Tribes Hill, Schenectady,
Mechanicville, Hadley, Troy, Ft Edward,
Gt Barrington, Falls
Roxbury, Stevenson Dam
Rapids, Williamsville, Lancaster,
Gardenville, Ebenezer, Gowanda
Wellsville, Portageville, Avon, Garbutt, Churchville
Figure 1: New York State Rivers and Gauge Locations
2. Data Analysis and Results
In order to distinguish between
large-scale and small-scale flooding events, it is important to consider the areal extent of the flooding. Though a measure of
square kilometers affected by these events would be the most effective way to
analyze this, limitations on river gauge data prevents such an in depth
analysis (Noyes, 2000). Therefore, the initial step to this research was
to acquire the top ten above flood stage (AFS) observations for each of the
gauge locations (not all gauges had a full period of 10 AFS floods, but were
included based on their location). Thus, only the floods of the highest
magnitudes were considered. These data were taken from the HYDROVIEW
program from both the Albany and
Buffalo NWSs’ AWIPS. These data were then
sorted by month and a monthly flood frequency was plotted for each CWA, (Figs.
2a-b) along with a seasonal flood frequency (Figs. 3a-b). The
seasons were based on standard meteorological seasonal definitions, for Winter (December-February), Spring (March-May), Summer
(June-August) and Fall (September-November). These figures show that for
the Albany CWA, approximately 55% of all river flooding observations for the 17
gauges occurred during the spring months, which is identical to the percentage
of springtime observations for the central NY region (Noyes, 2000).
However in Buffalo, the springtime
percentage of observations was slightly lower at 48% due to a higher number of
winter observations, 29%.
The monthly flood frequency, not magnitude (examined later),
analysis shows that for both county warning areas the month of March had the
highest number of all flooding observations (Figs. 2a-b). This is again
paralleling the research done in central NY (Noyes, 2000). It is in the
month of January and the early summertime months, that there are obvious
differences. Buffalo has a
larger frequency in January than Albany,
which is likely a result of the larger amount of ice jam observations in the Buffalo
region. Buffalo’s rivers and
creeks are much narrower than those of the Albany CWA basins, in particular the
Hudson and Mohawk Rivers.
This also causes the larger percentage of winter observations in Buffalo.
The Buffalo CWA also has a much larger monthly flood frequency in June than the
Albany area basins. This may
be a result of flash floods occurring in smaller creeks of the Buffalo
area basin from storms developing along the lake breeze convergence
In order to consider the climatological magnitude of flooding in these areas, the
height above flood stage (HAFS) was calculated. For this
calculation, the actual crest and flood stage for each observation was taken from
the gauge information and subtracted. The monthly median HAFS charts
(Figs. 4a-b) reveal that there are many differences between the Albany
and Buffalo gauges with respect to
magnitude. The data for HAFS is not normalized thus it is highly skewed
for the months of August and November. High HAFS observations for those
months can be disregarded based on no or few AFS observations in both basins
for November and August. The results from Buffalo
for HAFS are rather level from month to month compared to those of Albany.
However for the fall months, the median HAFS is fairly high for both regions
considering the smaller percent of AFS observations for September to
November. This is primarily due to the increased amount of tropical
systems, which impact the Northeast. For 6 of the 17 Buffalo CWA gauges
the highest flood recorded was due to a tropical system, mainly Tropical Storm
Agnes and Tropical Storm Frederick. Due to these two storms, almost all
of the gauges had an AFS observation within their top ten floods. This is
also true for Albany however it was
for such storms as Hurricane Diane.
To further examine the reasons for these differences in
monthly distributions, it was necessary to examine the possible cause of each
flood (Figs. 5a-b). This was gone about in several ways. One of
these processes was to actually examine the antecedent weather conditions for
those observation dates using archived weather maps (stored in the Buffalo NWS)
and NCEP/NCAR Eta reanalysis datasets. However,
over half of the gauge observations included comments, which described the
specific reason for the flood. Thus, all of the flooding events were
organized into 6 categories: heavy rain (flood caused by a prolonged period of
rain with no snowmelt associated), snowmelt (flood due to increased surface
temperatures and no rainfall), ice jam (blockage of rivers due to an extreme
thaw and no precipitation), heavy rain/snowfall (flood with a thaw and
associated precipitation), flash flood (mainly an early to mid-summertime
event), and heavy precipitation associated with tropical systems. For lack of time and large amounts of data (over 300 flooding
events), this part of the research is not complete. In Albany’s
comments the term “FRESHET” was used to indicate some sort of thaw but does not
indicate whether there was heavy precipitation in addition to the thaw.
Therefore, Albany has only five
categories for flood causes.
reason for severe flooding is prolonged periods of rain creating saturated soil
conditions. The second largest reason for severe flooding is periods of
heavy rain with increased surface temperatures (heavy rain/snowmelt), (Fig.
5b). This is in conjunction with the monthly median HAFS and the monthly
AFS frequencies (Figs. 2b and 4b). Since March has the highest AFS
frequency, it would be expected that there must be abundant events with heavy
rain and early season thaws to cause the bulk of flooding events.
Tropical events are the second minimum for both Albany
and Buffalo but again in comparison
to HAFS, they are the biggest reasons for large-scale
severe flooding with respect to magnitude.
Since favorable months for floods AFS and months with the
largest HAFS were evaluated, along with possible causes of these floods, the
last step would be to examine where flooding is typically occurring.
Again since the top ten floods for each gauge were used, the areas susceptible
to the greatest HAFS will be the best indicators of these flood prone areas.
For the Buffalo gauges, highest
values of HAFS were predominant in the Genesee river basin
(Fig. 6b) but the largest HAFS occurred at the Olean
gauge along the Allegany River.
This may be a result of snowfall maximum across the Allegany Plateau in the
upper Genesee River
basin, giving way to large snowmelts with
associated heavy rain caused floods. The rather large HAFS in the Buffalo
area basin are likely due to abundant ice jams along those smaller creeks and
streams. Albany gauges
indicate large magnitude floods along the Mohawk River
at the Utica and Schenectady
gauges (Fig. 6a). Again, this may be an indication of large amounts of
snow in the higher elevations of the Adirondacks causing
runoff into the Mohawk River. Large flooding is
also evident in the Housatonic
River Basin at the Stevenson Dam
gauge. This is primarily a result of tropical storms, which caused 3 of
the top 10 floods for that gauge. Both
the Genesee and Mohawk
Rivers had near record flooding
from tropical events, skewing the HAFS, although the more frequent occurrence
of severe flooding, and most of the top 10 HAFS, were the result of rapid
snowmelt. It must be noted that results from gauge to gauge are highly
dependent upon the shape and depth of the river at that site and also the
topography of the land along the vicinity of the river.
3. Interpretation of Results
On average, March is the month
with climatologically warming daily temperatures causing heavy snowmelt.
Thus, river basins in both the Albany
and Buffalo region can expect a
flood threat maximum. Heavy rainfall in conjunction with these warmer
temperatures can enhance the magnitude of flooding. Also aiding in the
early spring floods is runoff from higher elevations into streams, creeks and
rivers, especially if the ground is still relatively frozen. Therefore,
the 55% and 48% spring seasonal distribution of AFS observations (Figs. 3a-b)
can be directly related to heavy rainfall, increased temperatures, and ice jams
(Figs. 5a-b) for both Albany basins and Buffalo basins.
During the summer months, the
increased HAFS can be attributed to heavy rainfall associated with convective
systems or systems with training echoes. Localized flash flooding (from
convective storms along the Lake Erie/Lake Ontario lake breeze boundaries)
occurring in the smaller creeks and streams of the Buffalo
area basin are most likely the reason for a 10% higher summertime percentage
than that of Albany basins.
However, even though both regions show signs of increased fall flooding due to
tropical systems, the Albany region
is 8% more vulnerable to excessive tropical rainfall (being closer to the coast).
These tropical systems have caused several of the most intense floods magnitude
wise for both regions.
It should be noted that flooding
at certain gauge locations might be highly skewed since certain efforts of
flood control in recent years. For example, the Avon
gauge in the Genesee River
basin was prone to many problems and as a result,
flood control was installed at Mt. Morris.
On the other hand, the Stevenson Dam gauge off the Housatonic River,
mirrors the Albany region’s late summer, early fall increase in flooding due to
4. Summary and Future Work
Again, the month of March has the
highest threat of flooding along with the highest HAFS for both regions (both
in frequency (AFS) and magnitude (HAFS)). Though AFS observations may be
lower (in frequency of occurrence) in the summertime and fall months in both
regions, the HAFS plots indicate that when these floods occur, they tend to be
large in magnitude. The majority of these results are in perfect
agreement with the previous work done in Central NY.
This brief analysis of river
flooding along major basins of the Albany
and Buffalo county warning areas
has allowed for a climatological monthly evaluation
of flood threat. The climatology considers not only AFS observations
by month but also median HAFS observations both monthly and by location.
Basic causes of the top ten flooding events for each gauge are also used to
explain the monthly differences in the climatology for each region. Thus,
areas susceptible to minor or moderate flooding can be distinguished based on
time of year.
In order to continue this
analysis, there needs to be more in depth examinations of the synoptic and mesoscale conditions preceding and during flooding
events. This mainly needs to be done for the Albany
region events in which the term “FRESHET” was used
indicate the possible cause of flooding. However, it would be of great
interest to study the ground conditions prior to the event (soil moisture and
how much snow is on the ground) along with the exact time in which the flood
occurred. This entire analysis would prove to be useful to many other
areas outside of NY and even outside of the Northeast. Though combining
these results and those of the Central NY region into
one easily accessible dataset would give forecasters a basic reference to past
flooding events and also allow them to compare flooding events by region.
Both the Albany NWS and Buffalo NWS provided much of the
motivation for this research. Special thanks to Tom Niziol (SOO), Steve McLaughlin (hydrology focal point), and
Bill Hibbert of the Buffalo NWS for their assistance
and training on usage of the Hydroview program.
Also thanks to Tom Wasula of the Albany NWS.
Noyes, Matthew C., A Preliminary Climatological
Analysis of River Flooding Along Major Central New York River Basins, 2000.