% Example 12-5: Water flow in a river

% Width of the river
w = 8;

% Data measured
%   d      Day of year
%   h      Height of water
%   speed  Velocity of water

d =     [1  32  60  91 121 152 182 213 244 274 305 335 366];
h =     [2 2.1 2.3 2.4 3.0 2.9 2.7 2.6 2.5 2.3 2.2 2.1 2.0];
speed = [2 2.2 2.5 2.7 5   4.7 4.1 3.8 3.7 2.8 2.5 2.3 2  ];

% Flow rate Q
Q = speed.*w.*h;

% Integrate with trapz using the data to find
% volume in cubic meters
Vol = 60*60*24*trapz(d, Q)

% Plot flow rate over the time interval
plot(d, Q)
xlabel('Day'); ylabel('Flow Rate (m^3/s)');