Streamflow model of Wisconsin River for estimating flood frequency and volume

Abstract

A set of daily streamflow-routing models are used to simulate Streamflow at 10 sites along the Wisconsin River for water years 1915-76, to determine the effects the reservoir system has on flood discharges. Streamflow is simulated under the following two conditions: (1) No reservoirs are in the system and (2) all of the present reservoirs are in place and operated with current rules. At Wisconsin Dells, 20 miles upstream from Portage, daily Streamflow hydrographs are estimated for the 10-, 50-, 100-, and 500-year floods. These were determined from statistical analysis of the simulated daily streamflows for the condition of all reservoirs in place. The reservoirs have a significant impact on floods. The mean annual flood peak at Wisconsin Dells is lowered about 20 percent from 43,000 cubic feet per second for the simulated, unregulated condition to 34,000 cubic feet per second for the simulated, regulated condition. The 100-year flood peak at Wisconsin Dells is reduced about 10 percent (92,000 to 82,000 cubic feet per second) between the simulated, unregulated and simulated, regulated conditions. The 100-year flood peak at Wisconsin Dells, computed from the simulated, regulated Streamflow data for the period 1915-76, is 82,000 cubic feet per second, including the effects of all the reservoirs in the river system, as they are currently operated. It also includes the effects of Lakes Du Bay, Petenwell, and Castle Rock which are significant for spring floods but are insignificant for summer or fall floods because they are normally maintained nearly full in the summer and fall and have very little storage for floodwaters. L. L. Sheerar of WVIC and M. 0. Andrae of Wisconsin River Power Co. gave advice and instruction on operation of the reservoir system and hydroelectric dams which was necessary for the modeling. M. J. Mezzo and T. L. Hampton of the Wisconsin Department of Natural Resources obtained the reservoir stage records from WVIC and CWPC, computed daily changes in storage, and provided these data on magnetic tape for computer processing. The U.S. Army Corps of Engineers gave advice and assistance in the statistical analysis of the simulated streamflow records and in computation of flood hydrographs for Wisconsin Dells. DATA BASE Data used in digital modeling consisted of (1) daily streamflow data from 18 U.S. Geological Survey gaging stations, (2) reservoir stage data from WVIC, and (3) stage data from hydroelectric pools from CWPC. Locations of the U.S. Geological Survey gaging stations used in this report are shown on plate 1. Their full names, periods of record, and drainage areas are summarized in table 1. For simplicity all gaging stations on the Wisconsin River will be referred to by the location, for example, the Wisconsin River at Rainbow Lake near Lake Tomahawk will be referred to as Rainbow Lake. Gages on tributary streams will be referred to simply by the name of the river, unless more detail is required to avoid confusion. Locations of these gaging stations are also shown in a schematic diagram in f...

Simulated recruitment of riparian trees and shrubs under natural and regulated flow regimes on the Wisconsin River, USA

“…Based on differences between the natural and regulated flow scenarios (Krug and House, 1980), the effects of flow regulation on Wisconsin River flows are qualitatively similar to those found on other regulated rivers, with reduced peak flows, higher base flow and lower flow variability. The severity of these impacts, however, is less than on many rivers in the western US, such as the Missouri (Johnson, 1992), the Green (Cooper et al, 1999) and the Colorado (Schmidt et al, 1998).…”

“…In contrast to these western rivers, the storage capacity ( Figure 2) and annual drawdown of the reservoirs on the Wisconsin are not large. The dams are operated on a run-of-the-river basis, more or less following natural, climate-induced seasonal patterns of flow, but reducing their amplitude through some capture of flood waters in the spring and release of extra flow during late summer, fall and winter (Krug and House, 1980). In contrast to the effects of regulation on meandering rivers (Williams and Wolman, 1984;Rood and Mahoney, 1990;Johnson, 1998), flow regulation on the island-braided Wisconsin may create more favourable conditions for vegetation establishment and persistence.…”

“…Flow is modified by a series of upstream dams and reservoirs operated for power generation and water level stabilization. Although extensive alteration of flows occurred before 1900, much of the reduction in peak flows (10-20% at Wisconsin Dells, Krug and House, 1980) was due to the increase in storage capacity in the system (Figure 2) from the construction of the three largest reservoirs (Dubay, Petenwell and Castle Rock) between 1940and 1950(Krug and House, 1980Durbin, 1997). No new dams or other major flow alterations have occurred in the last 50 years.…”

“…Scenarios of regulated and unregulated flow were obtained from the output of a flow-routing model developed by Krug and House (1980) for the Wisconsin River at Wisconsin Dells, for the period of . The unregulated or 'natural' scenario simulates flow without flow impoundment by upstream reservoirs.…”

Ecosystem management and the conservation of river–floodplain systems

“…It has no major channel modifications, nor is the lower stretch of the river's floodplain leveed (with the exception of some waterfowl impoundments). However, it does experience reduced flooding due to an extensive system of dams and reservoirs upstream (Krug and House, 1980;Pfeiffer, 2000). That, combined with a shorter history of extensive human use, means that the natural system does not require the intensive interventions that its German counterpart does.…”