Spring Runoff Update

jen Clark - Utah Lake copy

Snow fall in December and January was nearly twice the normal amounts. Snow fall in February did not continue at that pace, but was still at, or above normal amounts. Current snow pack depths (water equivalent) at key gauging stations at higher elevations in the mountains east of Provo are now at 33 – 37”, well above normal for this time of year (21 – 23”). With average snow fall in March, peak snow packs this spring will be 165 – 185% of normal.

These are big numbers, but not necessarily historic. This magnitude of March 1st snow pack has been reached five times in the last 40 years. We saw high volumes of runoff each of those years, but high peak flows were experienced in only three of them. High peak flows are experienced when spring temperatures bring the majority of the runoff out in a couple of weeks rather than over a few months.

Forecasts

There is still a wide range of possibilities in terms of runoff scenarios, but they can begin to be described in broad generalities.  There are three areas of potential flooding in Provo, which will be described separately.

  • Utah Lake – In 2011, Utah Lake peaked at about 2½’ above compromise (normal elevation).  We do not expect to get anywhere close to that this year.  The last five years of drought dropped the elevation of the Lake down to nearly 7’ below compromise last fall; it is still nearly 5’ below compromise.  At this time in 2011, the Lake was already slightly above compromise.  Utah Lake will get close to compromise elevation for the first time is several years, but it is unlikely to get far above it.
  • Provo River – Flows in Provo River are currently in the 300 cfs (cubic feet per second) range.  We are likely to see flows near 1000 cfs for several weeks this spring.  Provo River flows in the 1700 – 2000 cfs range are likely for somewhere between a few days and a couple of weeks.  Flows in this range were experienced for a couple weeks in 2011.  Shallow water table elevations along the river will be noticeable, and homes which had to pump ground water in 2011 in the River Bottoms, River Grove and Lakeview Neighborhoods will likely have to again.
  • Frontal Canyons – Flows out of the frontal canyons (Rock, Slate and Little Rock) are most sensitive to spring temperatures and are difficult to predict.  Nevertheless, runoff flows are expected to flow through the Rock Canyon Basin Park and out of Slate Canyon for several weeks this spring.  However, unless a period of suddenly hot weather is seen, those flows will be well within manageable levels.

Preparations

Efforts to prepare for potential runoff scenarios have begun and are ongoing. Our supply of sandbags has been increased to 85,000. Stockpiles of sand are also being increased. Storm Water personnel will be inspecting and cleaning the frontal canyon channels and the Provo River to maximize capacity. Various locations will be evaluated for tree removal or other channel modifications.

Thanks goes to Greg Beckstrom for the update. I plan on sharing another update in early April, so stay tuned for more details.

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