Stochastic linear models are fitted to hydrologic data for two main reasons: to enable forecasts of the data one or more time periods ahead and to enable the generation of sequences of synthetic data. These techniques are of considerable importance to the design and operation of water resource systems. Short sequences of data lead to uncertainties in the estimation of model parameters and to doubts about the appropriateness of particular time series models. A premium is placed on models that are economical in terms of the number of parameters required. One such family of models is multiplicative seasonal autoregressive integrated moving average (Arima) models that have been described by G. E. P. Box and G. M. Jenkins. In this paper we illustrate the process of identifying the particular member of the family that fits logarithms of monthly flows, estimating the parameters, and checking the fit. The seasonal Arima model accounts for the seasonal variability in the monthly means but not the seasonal variability of the monthly standard deviations: for this reason its value is limited. The forecasting of flows one or more months ahead is described with an example.

Abstract. To provide data to investigate hypotheses about the evolution of channel networks, specifically the optimal channel network concept, discharge and channel properties were measured at 336 sites in a 121 km 2 basin over a 5-day period of reasonably steady flows. The data are also suitable for investigating how discharge increases down river channels. The data collection was a major logistical exercise which involved 80 person-days in remote field locations. In the expectation that the data will be of use to other researchers, this paper describes how the data were measured, checked and archived. The archive is available at http://www.niwa.cri.nz/hydrology/ashpage.htm and includes the associated time series of streamflow at the basin outlet and the channel network as plotted on 1:50,000 scale maps. The three-digit numbers on the map link to six-or sevendigit reference numbers for each measurement site. The six-or seven-digit numbers, which mimic the tree-like structure of the stream network but which were too lengthy to display on the map, were assigned as follows. Two kilometers upstream of the stream gauge the river divides into two main channels (Figure 1), the western branch (left-hand), named the Lillburn, and the eastern branch (right-hand), named the Ashley. The first digit of the numbers assigned for Ashley sites is "1" and the first digit for Lillburn sites is "2." For the Ashley the second and third digits identify the reach number between tributaries upstream from the stream gauge, whereas for the Lillburn, this number commenced at the Ashley/Lillburn confluence. The 139

Abstract. The paper describes data collected in a 158-km 2 basin for testing hypotheses underpinning the optimal channel network concept. Over a 4-day period, discharge, channel cross sections, and longitudinal slope were measured at 300 sites. Measured channel widths range from 0.050 to 16.60 m, mean depths range from 0.010 to 0.546 m, and mean water velocities range from 0.004 to 0.575 m/s. Bias in the site selection was checked by comparing measurements made at predefined distances upstream or downstream of the measurement section. Slope measurements were based on channel reach lengths typically of the order of 0.5 km. Since the data may be of use to other researchers, we have archived them on the World Wide Web (site http://www.cri.nz/hydrology/taieripage.htm) along with a 1:50,000 scale map and the associated time series of streamflow at the basin outlet during the measurement interval. For a catchment larger than a few hectares, this presents a significant logistical challenge, and not surprisingly, few such sets of data are reported in the literature. This data note presents watershed-wide data collected at 300 sites during a 4-day period of low summer flows. The extensive coverage provides data well suited for testing river basin heterogeneity concepts such as the optimal channel network (OCN) model. Here we briefly describe the data collection methods, indicate how the data may be accessed, and explore the applicability of the data to testing the OCN model.Since it is not practicable to measure flows at many locations simultaneously, a 4-day period of low summer flows was selected, and field teams were deployed to take the necessary measurements. The data comprise discharge and channel property measurements at 300 sites along the channel network in ASCII format: associated data are (1) the stream channel network in PostScript format for the basin as shown on the New Zealand Map Series (NZMS) 260 (1:50,000) maps for the basin, and (2) a time series of discharge values at 15-min intervals for a stream gauge at the outlet of the catchment for the 4-day measuring interval. The latter enable adjustment of the measurements to a given time.The data analysis and the hypothesis tests are reported by Ibbitt [1997]. In the expectation that the data will be useful to other researchers in this field, we are making them available following the guidelines of Hornberger [1994].

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