Twin Lakes Hydrology Study

Independent hydrologist report shows Twin Lakes parcels are unfit for development and doing so may cause flooding to existing residents' basements and impact the flow of water into sensitive neighboring wetlands. 

 
 With even the slightest rain or snow, flooding and standing water are a common site on the lands Boulder County and the City of Boulder desire to develop with nearly 300 apartments. 

With even the slightest rain or snow, flooding and standing water are a common site on the lands Boulder County and the City of Boulder desire to develop with nearly 300 apartments. 

Twin lakes hydrology summary

For decades, neighbors in the Red Fox Hills and Twin Lakes neighborhoods have had flooding issues in their basements associated with the high water table in the area. Sump pumps run constantly from March through October. Any construction in the area will divert ground water towards existing neighborhoods and increase the issue of basement flooding. On the other hand, a wetland located immediately to the southeast derives much of its water from the same hydrologic system. Mitigating ground water so as not to exacerbate local basement flooding will directly affect water resources, critical to the wetland. 

The Twin Lakes Action Group retained McCurry Hydrology, LLC to research and assess two parcels, located at 6600 (south parcel) and 6655 (north parcel) Twin Lakes Rd, regarding hydrologic and soil suitability for a construction project, proposed by the Boulder County Housing Authority and Boulder Valley School District. Dr. McCurry stated that the Twin Lakes and irrigation ditches, located immediately north of the proposed project, provide ample water to supply the area’s shallow ground water. Infiltrating ground water feeds directly into the north parcel, maintaining a high water table. The high water table in the north parcel, in turn, maintains the high water table in the south parcel. Heavy rains and melting snow serve to elevate the already high water table. Local ground water then drains into the ephemeral stream system to the south which recharges water supplies to a local wetland. The high water table, underlying both parcels is also in continuity with ground water beneath the Twin Lakes and Red Fox Hills neighborhoods to the west and east, respectively, of the parcels under consideration. High water tables in the Twin Lakes and Red Fox Hills neighborhoods require installation of sump pumps to prevent basement flooding. Sump pumps run frequently, sometimes constantly, from March through October.

The weight of large, possibly three story, buildings on the parcels, should construction occur, would compress the soils beneath, squeezing water out and away. Much of that water will flow into the surrounding neighborhoods, increasing the risk of basement flooding. The degree of potential damage is directly proportional to the scale of development.

Dr. McCurry also described the soils as somewhat limited to very limited regarding suitability to construction as described by the Unified Soil Classification System.

Any effort to pump water out of the system to mitigate basement flooding issues associated with proposed construction will remove water presently available to the adjacent wetland, thereby affecting critical wildlife habitat. Again, the severity of water depletion in the wetlands is proportional to the scale of development.

 

References:

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READ THE Hydrology Analysis

Click here to download the preliminary hydrology report and here to download the more detailed findings from the independent hydrology study.