FLOOD08628

• County: Costilla
• Community: San Luis
• Stream Name: San Luis area drainageway
• Basin: Rio Grande
• Title: Master Drainage Study Town of San Luis
• Date: 12/1/1988
• Prepared For: San Luis
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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We al so reviewed the as-built drawings of the levee provided to WRC
by the CWCB. In addition to this information field survey data
including profile and cross sections of the levee and the floodplain
area to the east. Based on a 1 imited number of field shot cross
sect ions, WRC estab 1 i shed an approximate 100 year water surface
profile for the area adjacent to the levee. This profile and
corresponding floodplain are shown on Sheet 4 of 4 of the drawings.
Based on thi s data generated by the HEC-2 water surface profi 1 e
computer program, an estimate of the levee profile required to
provide 3.0 feet of freeboard could be established. That profile is
also shown on Sheet 4 of 4. The profile indicates that the
elevation at the top of the levee needs to be increased and average
of 1.5 feet from the southern and to approximately 600 feet north of
6th Street.

Two so il bori ngs were dri 11 ed in the 1 evee to determi ne the soi 1
type and approximate stability of the levee. Levee material
consists of medium dense, silty,' 'sandy, gravel and the underlying
base of organic clay. The levee is generally sparsely covered with
vegetation that contributes to its stability. Based on WRC's HEC-2
profil e, the 100 year depth at the 1 evee does not exceed 2.0 feet,
the structural integrity of the levee should not be threatened.

It should be noted that the level of accuracy of this profile may be
1 imited by the distance between cross sections (up to 2000 feet in
some 1 ocat ions) and WRC recommends that pri or to prepari ng
construction drawings for levee improvements, additional cross
sect ions at no greater than 500 foot i nterva 1 s be taken and the
HEC-2 run refi ned accordingly.

3. Alternative Solutions

I n order to provi de the requi red 3.0 feet of freeboard,
approximately 4700 lineal ft. of the levee will have to be raised by
an average of 1.5 feet. Within this stretch three openings in the
levee exist for the purpose of providing access in and out of Town,
namely Gaspar Street, 4th Street and 6th Street. The following

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