Santa Cruz – Upper

To provide comments on this watershed for consideration in the Floodplain Management Plan, contact Greg Saxe
Planning Manager
(520) 724-4633.
The portion of the watershed identified as the Upper Santa Cruz River extends from the Santa Rita Mountain ridge in the southeast, across the Santa Cruz River basin to the Sierrita Mountains in the southwest. Its northern terminus is south of Martinez Hill and Black Mountain and the northern boundary of the San Xavier District of the Tohono O’odham Nation, and includes the confluence of the major tributary, Lee Moore Wash. Excluding the Lee Moore Wash watershed, it is comprised of 336,918 acres. Largely unaltered by flood control works, the Upper Santa Cruz River has a wide, riverine floodplain. Nevertheless, it largely impacts agricultural lands. Flood insurance is recommended for any structure near the river or its tributaries. This watershed contains 11,475 acres of SFHA, 44,946 acres of locally identified floodplain and 48,968 acres of Pima County Regulated Riparian Habitat.

Flood Hazards

Maps

Click HERE to view the watershed map
Click HERE to view the outreach brochure

Floodplain Studies

Floodplain Study FP-011-1989 - Green Valley Drainageway No.9, CMG Drainage Engineering Inc., 1/12/1989.

Floodplain Study FP-028-1994 - Hydrology/Hydraulics Report for Demetrie Wash, McGovern, MacVittie, Lodge & Associates, Inc., 10/13/1994.

Floodplain Study FP-038-1999 - Sahuarita Basin Management Study, CMG Drainage Engineering Inc., 1/5/2000.

Floodplain Study FP-085-2014 - Green Valley Drainageways Basin Management Study (Large file:  40 MB PDF), Figure 4B and Figure 5 (Large file:  20 MB PDF), CMG Drainage Engineering, Inc., 6/27/2014.

Floodplain Study FP-097-2019 - Upper Santa Cruz RiskMAP Technical Data Notebook for Hydrologic and Hydraulic Mapping, JE Fuller, 03/25/2019.

Erosion Studies

There are currently no erosion studies in this watershed.

Areas of Interest (Known Issues, Gaps, Problems and Needs)

Issues Provided by Public and Stakeholder Input

No issues have been identified to date.

Issues from the District Flood Response Manual

8.15.1 Data Gathering Needs
• No site specific issues identified.

8.15.2 Frequently Flooded Structures and Properties Subject to Damage
• The Lee Moore Wash and tributaries to the Lee Moore have created head cuts and other erosional features that are a potential threat to structures in the vicinity of Camino San Matias and Calle San Julian. (T16S R14E Sec. 18)
• The Madera Highlands subdivision may not have been adequately designed to deal with flooding from the Santa Cruz River and Sawmill Canyon Wash. (T18S R13E Sec. 13)

8.15.3 Infrastructure
• Kolb Basin - Damage has occurred to both the rip rap splash pads at the bottom of the east side inlets. (T15S R15E Sec. 20)
• Kolb Basin - Some bank rill erosion has been getting pretty deep along the north bank and some small rip rap drainage spillways at these locations may be warranted. (T15S R15E Sec. 20) 
• Arroyo Chico basin complex - The outlet splash pad into Basin # 3 has a sizeable scour hole, four to five foot deep across the length of the concrete splash pad. This is slated to be repaired in 2016/17 by adding more very large rip rap boulders.. (T14S R14E Sec. 18)
• Arroyo Chico basin complex - The arch culvert outlet off of basin #1 collects sediment on the outlet splash pad which needs to be monitored and possibly removed to keep low flow events from stacking material in the arch culvert. (T14S R14E Sec. 18)

8.15.4 Safety Concerns
• Green Valley drainageway # 6, does not have enough capacity to convey the base flood. (T18S R13E Secs. 10, 11)
• Green Valley drainageway # 9 does not have enough capacity to convey the base flood. (T18S R13E Secs. 14, 15)
• Green Valley drainageway # 13 does not have enough capacity to convey the base flood. (T18S R13E Secs. 14, 15, 22, 23)
• Green Valley drainageway # 17 does not have enough capacity to convey the base flood. (T18S R13E Secs. 22, 23)
• Green Valley drainageway # 6 has vertical embankments. (T18S R13E Secs. 10 11)
• Green Valley drainageway # 9 has vertical embankments. (T18S R13E Secs. 14, 15)
• Santa Cruz River: The channel of the Santa Cruz River will contain the 10 year event (about 16,000 cfs) at the Green Valley Sewage Treatment facility. The channel upstream will not contain the 50-year event (about 32,000 cfs). Once it gets out in the right overbank, access along the Nogales highway could be compromised. In a 50-yr event someone in Sahuarita should monitor the highway and railroad adjacent to Madera Highlands. (T17S R14E Sec. 31)
• Santa Cruz River: The channel capacity of the Santa Cruz River at Pima Mine Road is 16,000 cfs according to the Flood Insurance Study. Head cutting has increased the channel capacity, so the threshold of concern is approximately 20,000 cfs. If flows break out the intersection of Pima Mine and Old Nogales will start to flood. (T16S R14E Sec. 31)

 

Recommendation of Actions and Floodplain Management Strategy

This section to be completed based on feedback received through the planning process.