Geomorphic Processes, Controls, and Transition Zones in the Lower Sabine River Jonathan D. Phillips Copperhead Road Geosciences, LLC 720 Bullock Place Lexington, KY 40508 (also University of Kentucky) Michael C. Slattery Institute for Environmental Studies Texas Christian University Fort Worth, TX 76129 (also TCU Department of Geology) FINAL REPORT June 2007 1 INTRODUCTION AND OVERVIEW This report is based on a cooperative research study of the geomorphology of the Lower Sabine River, Texas (and Louisiana). The study focussed on delineating major geomorphic process zones, identification of major geomorphic controls, and determination the location and primary controls over key “hinge points” or transition zones. The specific objectives of the project were to: (1) Develop a baseline characterization of the condition and behavior of the lower Sabine River (downstream of Toledo Bend reservoir). (2) Examine longitudinal (downstream) changes in flow processes and energetics, channel and valley morphology, and patterns of recent geomorphic change. (3) Classify the lower Sabine (based on items 1, 2) into geomorphic process zones. (4) Identify the primary controls—both contemporary and historic—of the geomorphic process zones. (5) Identify the current location, primary controls over, and potential future changes in critical transition zones. The report is presented in two parts. The first, Flow and Sediment Transport Regimes in the Lower Sabine River, provides the hydrologic framework for the study, with a specific emphasis on downstream changes in flow and sediment transport. The second part, Geomorphic Controls on Transition Zones in the lower Sabine River, Texas-Louisiana, presents the geomorphic zonation and interpretations of geomorphic controls. 2 TABLE OF CONTENTS Page Flow and Sediment Transport Regimes in the Lower Sabine River 5 Introduction 5 River Discharge 10 Flows in the Sabine Delta 18 Sediment Transport 20 Summary and Conclusions 23 References 24 Geomorphic Controls on Transition Zones in the lower Sabine River 26 Introduction 26 Study Area 27 Methods 32 Results 35 Interpretations 45 Discussion 51 References 52 Scope of Work 55 3 List of Tables Section 1: Flow and Sediment Transport Regimes in the Lower Sabine River Table 1. USGS gaging stations in the study area 12 Table 2. Gaging station reference flows 13 Table 3. Suspended sediment transport at Deweyville 19 Table 4. Fluvial sediment yields in SE Texas 20 Table 5. Cross-sectional stream power, bankfull flows 22 Table 6. Cross-sectional stream power, 2006 flood 22 Section 2: Geomorphic Controls on Transition Zones Table 1. Geological zones 35 Table 2. Geological zonation 35 Table 3. Valley confinement 36 Table 4. Network characteristics 36 Table 5. Sinousity zonation 37 Table 6. Slope zonation 38 Table 7. Paleomeander scars within the river valley 39 Table 8. Dimensions of modern river meanders and paleomeanders 40 Table 9. Point bar zonation 42 Table 10. Major reaches of the lower Sabine River 51 List of Figures Section 1: Flow and Sediment Transport Regimes in the Lower Sabine River Figure 1. Sabine River basin 6 Figure 2. Monthly precipitation as a proportion of the mean 7 Figure 3. Surface runoff, Sabine/Neches estuary 8 Figure 4. Water diversions as a proportion of total surface runoff 9 Figure 5. Water diversions, Sabine/Neches estuary 10 Figure 6. Gaging stations and other key locations in study area 11 Figure 7. Hydrograph, fall 2006 flood event 15 Figure 8. Mean daily flows, Burkeville 15 Figure 8. Mean daily flows, Bon Wier 16 Figure 10. 31-day discharge record (15-minute intervals), lower Sabine 17 Section 2: Geomorphic Controls on Transition Zones Figure 1. Study area 27 Figure 2. Paleomeanders near Bon Wier 30 Figure 3. Longitudinal profile 38 Figure 4. Point bars between Burr Ferry and Anacoco Bayous 41 Figure 5. Schematic diagram of river zonation 43 Figure 6. Sabine River valley, vicinity of Cutoff Bayou 45 Figure 7. Geomorphic interprestation of area in figure 6 46 Figure 8. Topographic lineations near Big Cow Creek 49 4 FLOW AND SEDIMENT TRANSPORT REGIMES IN THE LOWER SABINE RIVER INTRODUCTION Runoff and discharge in the lower Sabine River is influenced by the climate and hydrologic response of the drainage basin, releases from Toledo Bend Reservoir, water withdrawals, and tidal and coastal backwater effects. The flow along the channel and valley is also influenced by (as well as influencing) the geomorphology. This section outlines and analyzes the flow regime of the river, in the context of a consideration of geomorphic controls on transition zones in the lower Sabine. The study area includes the Sabine River from the Toledo Bend reservoir to the Sabine Lake estuary, along the border of Texas and Louisiana. The Sabine River has a total drainage area of 25,267 km2, of which 6,676 km2 (26%) is downstream of the Toledo Bend dam (Fig. 1). The climate is humid subtropical, with a mean annual precipitation of 1100 to 1200 mm. Precipitation is year-round, but mid-summer droughts and low flows are common. Land use is predominantly forest, but a significant amount of grazing land is present. Urban and industrial land uses are limited. Monthly precipitation for the Sabine Lake area as a proportion of the 1941-2005 mean value is shown in Figure 2. A minor shift toward higher values is evident since the late 1970s. Total estimated inflow to the estuary from surface runoff is shown in Fig. 3. Toledo Bend Reservoir and Dam Toledo Bend Reservoir straddles the Louisiana-Texas border, and extends from the dam upstream about 105 km to Logansport, LA. The 750 km2 surface area at normal water levels makes Toledo Bend the fifth largest artificial water body in the U.S.A. The controlled storage capacity is 5.522 km3 (4,477,000 acre-feet). The project was constructed by the Sabine River Authority (SRA) of Texas and the SRA of Louisiana, with dam construction beginning in 1964, and completion in 1967. The hydroelectric power plant began operation in 1969. The primary purposes are water supply, hydroelectric power generation, and recreation. The dam is not operated to perform flood control functions. The SRA of Texas estimates a dependable water yield of 7.07 million cubic meters per day (818 m3 sec-1). The earth fill Toledo Bend Dam is more than 3,400 m long, with a maximum height of about 34 m. The design flow of the spillway is 8,212 m3 sec-1 (290,000 cfs). A minimum constant flow of about 5.7 m3 sec-1 (200 cfs) is maintained via the spillway, but most of the flow is passed through the hydroelectric turbines. Maximum recorded release was 3,239.5 m3 sec-1, and a typical flow during turbine operation is 200 to 300 m3 sec-1. 5 Figure 1. Sabine River Basin. 6 ( mean Figure http://hyper20.twdb.state.tx.us/data/bays_estuaries/hydrologypage.html Monthly Precipitation/Mean 0.00 1.00 2.00 3.00 4.00 5.00 6.00 value. 2. 1941 Monthly 1942 Based 1944 1946 1948 precipitation on 1950 1952 data 1953 1955 from 1957 for 1959 the 1961 the 1963 Texas 1964 Sabine/Neches 1966 1968 Water 1970 1972 1974 Development 1975 estuary 1977 1979 1981 1983 as 1985 Board a 1986 proportion 1988 1990 1992 ). 1994 1996 of 1997 the 1999 2001 2003 2005 7 7.0 6.0 5.0 4.0 3.0 Monthly Runoff/Mean 2.0 1.0 0.0 1941 1981 1974 1953 1950 1946 1957 1942 1966 1959 1968 1961 1996 2003 1955 1977 1952 1986 1948 1970 1979 1988 1944 1972 1994 2001 1963 1964 1992 1999 1983 1975 1985 1997 1990 2005 Figure 3. Surface runoff into the Sabine/Neches estuary as a percentage of the mean value. Based on monthly model calculations of the Texas Water Development Board (http://hyper20.twdb.state.tx.us/data/bays_estuaries/hydrologypage.html) Withdrawals The SRA of Texas operates an intake canal on one of the distributary channels of the lower Sabine between Deweyville and Orange. The Gulf Coast Canal system has a capacity of about 16 m3 sec-1, with water supplied primarily to industrial and municipal users. This maximum capacity represents about 12.5 percent of median and 6.7 percent of mean flow at the Deweyville gage. Some diversions occur on the Louisiana side, but no data on these could be obtained. The Texas Water Development Board conducted inflow and water balance studies for the Sabine Lake (Sabine/Neches) estuary, which includes both the Sabine and Neches Rivers and some small coastal basins. The known or estimated total diversions relative to inflow (gaged river flows plus model estimates of ungaged areas) is shown in figure 4. The 1941-2005 trends in diversions as a percent of the mean, shown in Figure 5, show obvious seasonal patterns associated primarily with agricultural irrigation. Significant diversions between Toledo Bend and Sabine Lake occur only downstream of Cutoff Bayou on both the Texas and Louisiana sides. 8 1.8 1.6 1.4 1.2 1.0 0.8 0.6 Water Diversion/Total surface runoff 0.4 0.2 0.0 1941 1981 1974 1953 1950 1946 1957 1942 1966 1959 1968 1961 1996 2003 1955 1977 1952 1986 1948 1970 1979 1988 1944 1972 1994 2001 1963 1964 1992 1999 1983 1975 1985 1997 1990 2005 Figure 4. Water diversions for the Sabine/Neches estuary as a proportion of total surface runoff. Based on monthly model calculations of the Texas Water Development Board (http://hyper20.twdb.state.tx.us/data/bays_estuaries/hydrologypage.html) 9 3.5 3.0 2.5 2.0 1.5 Monthly Diversions/Mean 1.0 0.5 0.0 1941 1981 1974 1953 1950 1946 1957 1942 1966 1959 1968 1961 1996 2003 1955 1977 1952 1986 1948 1970 1979 1988 1944 1972 1994 2001 1963 1964 1992 1999 1983 1975 1985 1997 1990 2005 Figure 5.