The average annual precipitation in the basin ranges from 31 inches in the northern part to 35 inches in the southern part (about 90 % in the form of rainfall, USDA 1981). About 70 % of the rainfall occurs in the 150-180 day growing season (USCOE 1973). Average annual snowfall ranges from 20 to 30 inches across the basin, increasing from south to north (USDA 1981, MDNR 1986b). Runoff ranges from four to six inches annually. Certain factors influence runoff severity such as soil erodibility, soil permeability, soil saturation, land cover, and the time-span over which the runoff occurs (MDNR 1986b). Runoff and discharge are primarily driven by rainfall (Figure Hy01; data from Graham, Missouri gauging station). Discrepancies in discharge, as a function of precipitation for Figure Hy01, were probably caused by snowmelt in February and localized heavy rainfall in the upper portion of the basin in June. The basin in Missouri is in the driest part of the state, and due to highly variable annual precipitation has been subject to extensive dry periods.
There are two active United States Geological Survey (USGS) gauging stations (Figure Hy02) and one active partial records gauging station in the Nodaway River basin. The three stations are all located on the mainstem Nodaway River near the towns of Graham, Missouri, Clarinda, Iowa, and Massena, Iowa (USGS 1995a, USGS 1996a). Inactive gauge stations are located near Villisca, Iowa, Burlington Junction, Missouri, and Oregon, Missouri. A complete listing of locations and details for all six can be found in Table Hy01.
Permenant and Intermittant Streams
There are 156 third order and larger streams in the Nodaway River basin (Table Hy02). The permanence/intermittence of particular streams can be determined from 7.5 minute series topographical maps found in the coverage in Figure Hy03. Permanent streams are indicated with solid blue lines and intermittent streams are indicated with dashed blue lines. The mainstem Nodaway was classified as permanently flowing for 52 of its 61 miles in Missouri (Funk 1968). Based on current USGS 7.5 minute maps there are 485 miles of permanently flowing and 138 miles of intermittently flowing streams and rivers, fourth order or higher, in the Nodaway River basin. Most lower order streams in the basin are intermittent. Increased intermittence, resulting from lower base flows and sedimentation, is occurring throughout the basin.
The average discharge for the Nodaway River near Graham, MO from water years 1983-1996 was 1,011 cubic feet per second (cfs). The maximum instantaneous peak flow on the Nodaway near Graham was 78,300 cfs in 1993, and the maximum instantaneous peak flow on the West Nodaway was 31,100 cfs at Clarinda, IA in 1947 (Table Hy03). The Nodaway River makes up 0.4 % of the drainage area and about 1 % of the average annual flow of the Missouri River at their confluence.
The Nodaway River has contributed as much as 20 percent to the Missouri River flood crest when concurrent high flows occurred (USCOE 1973). Flood magnitude in cubic feet per second for various recurrence intervals on the Nodaway River at Burlington Junction, Missouri was calculated to be: 12,300 for two year, 22,600 for five year, 30,500 for ten year, 41,200 for twenty-five year, 50,000 for fifty year, and 58,400 for 100 year flood events (Hauth 1974). The Nodaway River basin has highly variable flows as shown by its flow duration curve (Figure Hy04). Streams in the basin tend to rise and subside swiftly in response to precipitation events.
7-Day Q2 And Q10 Low Flows
Streams in the Dissected Till Plains Region, including the Nodaway River, have poor low flow potentials due to low hydraulic conductivity of area soils and poor land use practices. Low flows in the basin usually occur in the months of August, September, and October (Skelton 1976). Low flow characteristics can usually be generalized in plains streams based upon the size of the drainage area. Streams with basin areas less than 100 mi2 will almost always have 7-day average minimum flows at recurrence intervals of two years (7-day Q2) of zero. About 60 percent of plains streams with drainage areas of 100 to 200 mi2 will have 7-day Q2 of zero and the remainder will have 7-day Q2 of 0.1 to 1.0 cfs. This method is unreliable for basins with drainage areas larger than 200 mi2 and field observations are required. The 7-day average minimum flows at 10 year intervals (7-day Q10) for drainage basins of 200 mi2 or less are almost always zero. About 70 percent of plains streams with drainage areas or 200 to 1,000 mi2 will have 7-day Q10 of zero and the remainder will have 7-day Q10 of 0.1 to 1.5 cfs. For drainage basins larger than 1,000 mi2 field observations of flow are required (Skelton 1976). Table Hy04 shows low flow data for reporting gauge stations in the Nodaway River basin.
Dam and Hydropower Influences
There are no major dams in the basin. There are a few moderate-sized reservoirs and a large number of small ponds in the Nodaway River basin. The larger bodies of water are public impoundments. Due to small size and ease of construction, the number of ponds can change very rapidly. Many ponds are built without needing permits and statistics on ponds are usually compiled by county rather than watershed. These factors complicate getting accurate, up-to-date information on ponds. Concern exists over the effects these ponds have on low-flow conditions as they intercept runoff and allow little or no adjustment for maintenance of stream flows.