FLOOD04954

• County: Costilla
• Community: San Luis
• Basin: Rio Grande
• Title: Subsurface Drainage Feasibilty Study
• Date: 9/1/1996
• Prepared For: Costilla County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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drained to prevent recharge from taking place. Some of these areas may be classified as
wetlands requiring permits prior to filling or drainage.

The town has a surface irrigation system throughout. This earthen ditch system offers
considerable opportunity for seepage and flows through many highly permeable soils. Plans
should be developed to line or pipe this system. Previous water table surveys have shown
that the water table is influenced heavily by irrigation.

The Montez Ditch diverts water from the Rito Seco near the crossing under Colorado
Highway 159 and then flows in a southerly direction one block east of the highway. The
ditch is in poor condition and restricts the movement of water through the town. Standing
water can be observed in the ditch throughout the year, and the ditch is full of water-
dependent plants that indicate the ditch is never without water. The condition of the ditch is
worse than it was in 1979, and so the ditch should either be properly maintained or
abandoned altogether.

The source of the standing water in the Montez ditch is from numerous artesian wells that
are left to flow year round. These wells should be properly capped in order to prevent the
continuous flow of water when it is not needed. Since there are several wells located along
the Montez Ditch, it is likely that more wells are located in other areas of the town. These
other wells, if any, should also be capped.

The drainage investigation conducted in 1987 found the ground water movement in the
Northern part of town to be from the North with only a minor impact from the Rito Seco. It
is suspected that the influence of the Rito Seco increases further south. The change in the
stream channel has tended to increase the water table close to the channel. It is highly likely
that this effect extends well away from the channel. The land slope is to the south and the
water table slope should tend to parallel the ground surface. As such, the water table effect
from the Rito Seco should increase as the channel flows toward the southeast. The only
way to stop water entering the area from the Rito Seco is to install an interceptor drain line.
The exact effect of the Rito Seco can only be determined with a water table investigation.

The Vega Commons (Vega) is located to the east of the town. This is a large wetland area
and could be a source of some of the drainage problems. An existing drainage ditch is
located along the west side of the Vega, but it is in very poor condition. While it is unlikely
that a significant groundwater impact is resulting from the Vega, the existing ditch should
be restored and maintained. Additional drainage of the Vega should not be done. Drainage
of the Vega would be very detrimental to its ecology, and may be subject to the jurisdiction
of the Corps of Engineers 404 permitting process.

In summary, a subdrain system is the surest way to solve the groundwater problems, but
will be the most expensive solution. It must be emphasized that the observations and
opinions presented in this section are the opinions of the author, William Wittwer, and are
based on past investigations as well as conversations with local residents.

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