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<br />NPIC RESERVOIR #5 SPILLWAY
<br />
<br />NPIC Reservoir #5 is impounded by an earth dam with a maximum height of 34 feet and a total crest
<br />length of approximately 2100 feet and provides approximately 8400 acre-feet of water storage. A
<br />major rehabilitation of the dam and outlet structure was completed in 1995. At some point during the
<br />State Engineers Office (SEO) review of the completed rehabilitation project it was discovered that the
<br />existing spillway does not have the capacity to pass 75 % of the Probable Maximum Flood (PMF) as
<br />required, The existing spillway at NPIC Reservoir #5 is approximately 250 long and is located at the
<br />right abutment. The control section is protected on the upstream side by riprap but there is no cutoff
<br />wall or downstream erosion protection. Hydrology studies show that water will spill around the east
<br />end of the dam at upper stages of the PMF, North Poudre Irrigation Company does not own this land
<br />at the east end of the dam nor are there any flood easements at this location, Two options were
<br />reviewed for bringing the spillway into compliance.
<br />
<br />The first option considered using the low section at the east end of the dam as additional spillway, This
<br />section is now approximately 1.5 feet below the dam crest and 3,5 feet above the existing spillway,
<br />Adding spillway at this location would require an easement both for construction of the spillway and an
<br />easement for flooding downstream of the spillway, This spillway work would be in addition to making
<br />the necessary improvements (cutoff wall, grading, and downstream protection) on the west spillway. A
<br />cost estimate for this option may be found in Table 3,
<br />
<br />TABLE 3. COST ESTIMATE NPIC #5 SPILLWAY OPTION # 1.
<br />
<br />ITEM DESCRIPTION QUANTITY UNITS UNIT PRICE AMOUNT
<br />1. MOBILIZATION, INSURANCE. BONDS 1.00 L.S. $8.000.00 $8,000,00
<br />2. STRIPPING AND CLEARING 1.00 L.S. $3,000,00 $3,000.00
<br />3, EARTH EXCAVATION 4600,00 C,Y. $2,00 $9,200.00
<br />4. EARTH FILL 4000,00 C,Y. $3,00 $12.000,00
<br />5, SPOIL MATERIAL 700.00 C.Y, $1.50 $1,050,00
<br />6, RIPRAP 2100.00 TON $25 ,00 $52.500,00
<br />7. RIPRAP BEDDING 750.00 TON $18.00 $13,500,00
<br />8, ROAD BASE 425,00 TON $18.00 $7,650,00
<br />9. CONCRETE 100.00 C,Y, $350,00 $35,000,00
<br />10, SEEDING 7,00 ACRE $1,000,00 $7,000,00
<br />11. EASMENTS 1.00 L.S, $60,000,00 $60,000.00
<br />12, ENGINEERING AND CONTINGENCIES 1.00 L.S. $68,000.00 $68,000.00
<br />
<br />TOTAL $276,900.00
<br />
<br />The second option includes improving and enlarging the existing spillway at the right abutment to meet
<br />State requirements, raising the low section at the left abutment to the same height as the existing dam
<br />crest, and purchasing the necessary easements at both ends of the dam, The existing spillway length
<br />would need to be increased to approximately 380 feet to pass 75 % of the PMF. This new extended
<br />spillway would require a concrete cutoff wall one foot thick and four feet deep extending its entire
<br />length with rip rap extending 5 feet upstream and 20 feet downstream of the wall. The channel
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